tor-browser

pass2_strategy.c (180457B)

---

/*
* Copyright (c) 2019, Alliance for Open Media. All rights reserved.
*
* This source code is subject to the terms of the BSD 2 Clause License and
* the Alliance for Open Media Patent License 1.0. If the BSD 2 Clause License
* was not distributed with this source code in the LICENSE file, you can
* obtain it at www.aomedia.org/license/software. If the Alliance for Open
* Media Patent License 1.0 was not distributed with this source code in the
* PATENTS file, you can obtain it at www.aomedia.org/license/patent.
*/

/*!\defgroup gf_group_algo Golden Frame Group
* \ingroup high_level_algo
* Algorithms regarding determining the length of GF groups and defining GF
* group structures.
* @{
*/
/*! @} - end defgroup gf_group_algo */

#include <assert.h>
#include <limits.h>
#include <stdint.h>

#include "aom_dsp/aom_dsp_common.h"
#include "aom_mem/aom_mem.h"
#include "config/aom_config.h"
#include "config/aom_scale_rtcd.h"

#include "aom/aom_codec.h"
#include "aom/aom_encoder.h"

#include "av1/common/av1_common_int.h"

#include "av1/encoder/encoder.h"
#include "av1/encoder/firstpass.h"
#include "av1/encoder/gop_structure.h"
#include "av1/encoder/pass2_strategy.h"
#include "av1/encoder/ratectrl.h"
#include "av1/encoder/rc_utils.h"
#include "av1/encoder/temporal_filter.h"
#if CONFIG_THREE_PASS
#include "av1/encoder/thirdpass.h"
#endif
#include "av1/encoder/tpl_model.h"
#include "av1/encoder/encode_strategy.h"

#define DEFAULT_KF_BOOST 2300
#define DEFAULT_GF_BOOST 2000
#define GROUP_ADAPTIVE_MAXQ 1

static void init_gf_stats(GF_GROUP_STATS *gf_stats);
#if CONFIG_THREE_PASS
static int define_gf_group_pass3(AV1_COMP *cpi, EncodeFrameParams *frame_params,
                                int is_final_pass);
#endif

// Calculate an active area of the image that discounts formatting
// bars and partially discounts other 0 energy areas.
#define MIN_ACTIVE_AREA 0.5
#define MAX_ACTIVE_AREA 1.0
static double calculate_active_area(const FRAME_INFO *frame_info,
                                   const FIRSTPASS_STATS *this_frame) {
 const double active_pct =
     1.0 -
     ((this_frame->intra_skip_pct / 2) +
      ((this_frame->inactive_zone_rows * 2) / (double)frame_info->mb_rows));
 return fclamp(active_pct, MIN_ACTIVE_AREA, MAX_ACTIVE_AREA);
}

// Calculate a modified Error used in distributing bits between easier and
// harder frames.
#define ACT_AREA_CORRECTION 0.5
static double calculate_modified_err_new(const FRAME_INFO *frame_info,
                                        const FIRSTPASS_STATS *total_stats,
                                        const FIRSTPASS_STATS *this_stats,
                                        int vbrbias, double modified_error_min,
                                        double modified_error_max) {
 if (total_stats == NULL) {
   return 0;
 }
 const double av_weight = total_stats->weight / total_stats->count;
 const double av_err =
     (total_stats->coded_error * av_weight) / total_stats->count;
 double modified_error =
     av_err * pow(this_stats->coded_error * this_stats->weight /
                      DOUBLE_DIVIDE_CHECK(av_err),
                  vbrbias / 100.0);

 // Correction for active area. Frames with a reduced active area
 // (eg due to formatting bars) have a higher error per mb for the
 // remaining active MBs. The correction here assumes that coding
 // 0.5N blocks of complexity 2X is a little easier than coding N
 // blocks of complexity X.
 modified_error *=
     pow(calculate_active_area(frame_info, this_stats), ACT_AREA_CORRECTION);

 return fclamp(modified_error, modified_error_min, modified_error_max);
}

static double calculate_modified_err(const FRAME_INFO *frame_info,
                                    const TWO_PASS *twopass,
                                    const AV1EncoderConfig *oxcf,
                                    const FIRSTPASS_STATS *this_frame) {
 const FIRSTPASS_STATS *total_stats = twopass->stats_buf_ctx->total_stats;
 return calculate_modified_err_new(
     frame_info, total_stats, this_frame, oxcf->rc_cfg.vbrbias,
     twopass->modified_error_min, twopass->modified_error_max);
}

// Resets the first pass file to the given position using a relative seek from
// the current position.
static void reset_fpf_position(TWO_PASS_FRAME *p_frame,
                              const FIRSTPASS_STATS *position) {
 p_frame->stats_in = position;
}

static int input_stats(TWO_PASS *p, TWO_PASS_FRAME *p_frame,
                      FIRSTPASS_STATS *fps) {
 if (p_frame->stats_in >= p->stats_buf_ctx->stats_in_end) return EOF;

 *fps = *p_frame->stats_in;
 ++p_frame->stats_in;
 return 1;
}

static int input_stats_lap(TWO_PASS *p, TWO_PASS_FRAME *p_frame,
                          FIRSTPASS_STATS *fps) {
 if (p_frame->stats_in >= p->stats_buf_ctx->stats_in_end) return EOF;

 *fps = *p_frame->stats_in;
 /* Move old stats[0] out to accommodate for next frame stats  */
 memmove(p->frame_stats_arr[0], p->frame_stats_arr[1],
         (p->stats_buf_ctx->stats_in_end - p_frame->stats_in - 1) *
             sizeof(FIRSTPASS_STATS));
 p->stats_buf_ctx->stats_in_end--;
 return 1;
}

// Read frame stats at an offset from the current position.
static const FIRSTPASS_STATS *read_frame_stats(const TWO_PASS *p,
                                              const TWO_PASS_FRAME *p_frame,
                                              int offset) {
 if ((offset >= 0 &&
      p_frame->stats_in + offset >= p->stats_buf_ctx->stats_in_end) ||
     (offset < 0 &&
      p_frame->stats_in + offset < p->stats_buf_ctx->stats_in_start)) {
   return NULL;
 }

 return &p_frame->stats_in[offset];
}

// This function returns the maximum target rate per frame.
static int frame_max_bits(const RATE_CONTROL *rc,
                         const AV1EncoderConfig *oxcf) {
 int64_t max_bits = ((int64_t)rc->avg_frame_bandwidth *
                     (int64_t)oxcf->rc_cfg.vbrmax_section) /
                    100;
 if (max_bits < 0)
   max_bits = 0;
 else if (max_bits > rc->max_frame_bandwidth)
   max_bits = rc->max_frame_bandwidth;

 return (int)max_bits;
}

static const double q_pow_term[(QINDEX_RANGE >> 5) + 1] = { 0.65, 0.70, 0.75,
                                                           0.80, 0.85, 0.90,
                                                           0.95, 0.95, 0.95 };
#define ERR_DIVISOR 96.0
static double calc_correction_factor(double err_per_mb, int q) {
 const double error_term = err_per_mb / ERR_DIVISOR;
 const int index = q >> 5;
 // Adjustment to power term based on qindex
 const double power_term =
     q_pow_term[index] +
     (((q_pow_term[index + 1] - q_pow_term[index]) * (q % 32)) / 32.0);
 assert(error_term >= 0.0);
 return fclamp(pow(error_term, power_term), 0.05, 5.0);
}

// Based on history adjust expectations of bits per macroblock.
static void twopass_update_bpm_factor(AV1_COMP *cpi, int rate_err_tol) {
 TWO_PASS *const twopass = &cpi->ppi->twopass;
 const PRIMARY_RATE_CONTROL *const p_rc = &cpi->ppi->p_rc;

 // Based on recent history adjust expectations of bits per macroblock.
 double damp_fac = AOMMAX(5.0, rate_err_tol / 10.0);
 double rate_err_factor = 1.0;
 const double adj_limit = AOMMAX(0.2, (double)(100 - rate_err_tol) / 200.0);
 const double min_fac = 1.0 - adj_limit;
 const double max_fac = 1.0 + adj_limit;

#if CONFIG_THREE_PASS
 if (cpi->third_pass_ctx && cpi->third_pass_ctx->frame_info_count > 0) {
   int64_t actual_bits = 0;
   int64_t target_bits = 0;
   double factor = 0.0;
   int count = 0;
   for (int i = 0; i < cpi->third_pass_ctx->frame_info_count; i++) {
     actual_bits += cpi->third_pass_ctx->frame_info[i].actual_bits;
     target_bits += cpi->third_pass_ctx->frame_info[i].bits_allocated;
     factor += cpi->third_pass_ctx->frame_info[i].bpm_factor;
     count++;
   }

   if (count == 0) {
     factor = 1.0;
   } else {
     factor /= (double)count;
   }

   factor *= (double)actual_bits / DOUBLE_DIVIDE_CHECK((double)target_bits);

   if ((twopass->bpm_factor <= 1 && factor < twopass->bpm_factor) ||
       (twopass->bpm_factor >= 1 && factor > twopass->bpm_factor)) {
     twopass->bpm_factor = fclamp(factor, min_fac, max_fac);
   }
 }
#endif  // CONFIG_THREE_PASS

 int err_estimate = p_rc->rate_error_estimate;
 int64_t bits_left = twopass->bits_left;
 int64_t total_actual_bits = p_rc->total_actual_bits;
 int64_t bits_off_target = p_rc->vbr_bits_off_target;
 double rolling_arf_group_actual_bits =
     (double)twopass->rolling_arf_group_actual_bits;
 double rolling_arf_group_target_bits =
     (double)twopass->rolling_arf_group_target_bits;

#if CONFIG_FPMT_TEST
 const int is_parallel_frame =
     cpi->ppi->gf_group.frame_parallel_level[cpi->gf_frame_index] > 0 ? 1 : 0;
 const int simulate_parallel_frame =
     cpi->ppi->fpmt_unit_test_cfg == PARALLEL_SIMULATION_ENCODE
         ? is_parallel_frame
         : 0;
 total_actual_bits = simulate_parallel_frame ? p_rc->temp_total_actual_bits
                                             : p_rc->total_actual_bits;
 bits_off_target = simulate_parallel_frame ? p_rc->temp_vbr_bits_off_target
                                           : p_rc->vbr_bits_off_target;
 bits_left =
     simulate_parallel_frame ? p_rc->temp_bits_left : twopass->bits_left;
 rolling_arf_group_target_bits =
     (double)(simulate_parallel_frame
                  ? p_rc->temp_rolling_arf_group_target_bits
                  : twopass->rolling_arf_group_target_bits);
 rolling_arf_group_actual_bits =
     (double)(simulate_parallel_frame
                  ? p_rc->temp_rolling_arf_group_actual_bits
                  : twopass->rolling_arf_group_actual_bits);
 err_estimate = simulate_parallel_frame ? p_rc->temp_rate_error_estimate
                                        : p_rc->rate_error_estimate;
#endif

 if (p_rc->bits_off_target && total_actual_bits > 0) {
   if (cpi->ppi->lap_enabled) {
     rate_err_factor = rolling_arf_group_actual_bits /
                       DOUBLE_DIVIDE_CHECK(rolling_arf_group_target_bits);
   } else {
     rate_err_factor = 1.0 - ((double)(bits_off_target) /
                              AOMMAX(total_actual_bits, bits_left));
   }

   // Adjustment is damped if this is 1 pass with look ahead processing
   // (as there are only ever a few frames of data) and for all but the first
   // GOP in normal two pass.
   if ((twopass->bpm_factor != 1.0) || cpi->ppi->lap_enabled) {
     rate_err_factor = 1.0 + ((rate_err_factor - 1.0) / damp_fac);
   }
   rate_err_factor = AOMMAX(min_fac, AOMMIN(max_fac, rate_err_factor));
 }

 // Is the rate control trending in the right direction. Only make
 // an adjustment if things are getting worse.
 if ((rate_err_factor < 1.0 && err_estimate >= 0) ||
     (rate_err_factor > 1.0 && err_estimate <= 0)) {
   twopass->bpm_factor *= rate_err_factor;
   if (rate_err_tol >= 100) {
     twopass->bpm_factor =
         AOMMAX(min_fac, AOMMIN(max_fac, twopass->bpm_factor));
   } else {
     twopass->bpm_factor = AOMMAX(0.1, AOMMIN(10.0, twopass->bpm_factor));
   }
 }
}

static int qbpm_enumerator(int rate_err_tol) {
 return 1200000 + ((300000 * AOMMIN(75, AOMMAX(rate_err_tol - 25, 0))) / 75);
}

// Similar to find_qindex_by_rate() function in ratectrl.c, but includes
// calculation of a correction_factor.
static int find_qindex_by_rate_with_correction(
   uint64_t desired_bits_per_mb, aom_bit_depth_t bit_depth,
   double error_per_mb, double group_weight_factor, int rate_err_tol,
   int best_qindex, int worst_qindex) {
 assert(best_qindex <= worst_qindex);
 int low = best_qindex;
 int high = worst_qindex;

 while (low < high) {
   const int mid = (low + high) >> 1;
   const double mid_factor = calc_correction_factor(error_per_mb, mid);
   const double q = av1_convert_qindex_to_q(mid, bit_depth);
   const int enumerator = qbpm_enumerator(rate_err_tol);
   const uint64_t mid_bits_per_mb =
       (uint64_t)((enumerator * mid_factor * group_weight_factor) / q);

   if (mid_bits_per_mb > desired_bits_per_mb) {
     low = mid + 1;
   } else {
     high = mid;
   }
 }
 return low;
}

/*!\brief Choose a target maximum Q for a group of frames
*
* \ingroup rate_control
*
* This function is used to estimate a suitable maximum Q for a
* group of frames. Inititally it is called to get a crude estimate
* for the whole clip. It is then called for each ARF/GF group to get
* a revised estimate for that group.
*
* \param[in]    cpi                 Top-level encoder structure
* \param[in]    av_frame_err        The average per frame coded error score
*                                   for frames making up this section/group.
* \param[in]    inactive_zone       Used to mask off /ignore part of the
*                                   frame. The most common use case is where
*                                   a wide format video (e.g. 16:9) is
*                                   letter-boxed into a more square format.
*                                   Here we want to ignore the bands at the
*                                   top and bottom.
* \param[in]    av_target_bandwidth The target bits per frame
*
* \return The maximum Q for frames in the group.
*/
static int get_twopass_worst_quality(AV1_COMP *cpi, const double av_frame_err,
                                    double inactive_zone,
                                    int av_target_bandwidth) {
 const RATE_CONTROL *const rc = &cpi->rc;
 const AV1EncoderConfig *const oxcf = &cpi->oxcf;
 const RateControlCfg *const rc_cfg = &oxcf->rc_cfg;
 inactive_zone = fclamp(inactive_zone, 0.0, 0.9999);

 if (av_target_bandwidth <= 0) {
   return rc->worst_quality;  // Highest value allowed
 } else {
   const int num_mbs = (oxcf->resize_cfg.resize_mode != RESIZE_NONE)
                           ? cpi->initial_mbs
                           : cpi->common.mi_params.MBs;
   const int active_mbs = AOMMAX(1, num_mbs - (int)(num_mbs * inactive_zone));
   const double av_err_per_mb = av_frame_err / (1.0 - inactive_zone);
   const uint64_t target_norm_bits_per_mb =
       ((uint64_t)av_target_bandwidth << BPER_MB_NORMBITS) / active_mbs;
   int rate_err_tol = AOMMIN(rc_cfg->under_shoot_pct, rc_cfg->over_shoot_pct);

   // Update bpm correction factor based on previous GOP rate error.
   twopass_update_bpm_factor(cpi, rate_err_tol);

   // Try and pick a max Q that will be high enough to encode the
   // content at the given rate.
   int q = find_qindex_by_rate_with_correction(
       target_norm_bits_per_mb, cpi->common.seq_params->bit_depth,
       av_err_per_mb, cpi->ppi->twopass.bpm_factor, rate_err_tol,
       rc->best_quality, rc->worst_quality);

   // Restriction on active max q for constrained quality mode.
   if (rc_cfg->mode == AOM_CQ) q = AOMMAX(q, rc_cfg->cq_level);
   return q;
 }
}

#define INTRA_PART 0.005
#define DEFAULT_DECAY_LIMIT 0.75
#define LOW_SR_DIFF_TRHESH 0.01
#define NCOUNT_FRAME_II_THRESH 5.0
#define LOW_CODED_ERR_PER_MB 0.01

/* This function considers how the quality of prediction may be deteriorating
* with distance. It comapres the coded error for the last frame and the
* second reference frame (usually two frames old) and also applies a factor
* based on the extent of INTRA coding.
*
* The decay factor is then used to reduce the contribution of frames further
* from the alt-ref or golden frame, to the bitframe boost calculation for that
* alt-ref or golden frame.
*/
static double get_sr_decay_rate(const FIRSTPASS_STATS *frame) {
 double sr_diff = (frame->sr_coded_error - frame->coded_error);
 double sr_decay = 1.0;
 double modified_pct_inter;
 double modified_pcnt_intra;

 modified_pct_inter = frame->pcnt_inter;
 if ((frame->coded_error > LOW_CODED_ERR_PER_MB) &&
     ((frame->intra_error / DOUBLE_DIVIDE_CHECK(frame->coded_error)) <
      (double)NCOUNT_FRAME_II_THRESH)) {
   modified_pct_inter = frame->pcnt_inter - frame->pcnt_neutral;
 }
 modified_pcnt_intra = 100 * (1.0 - modified_pct_inter);

 if ((sr_diff > LOW_SR_DIFF_TRHESH)) {
   double sr_diff_part = ((sr_diff * 0.25) / frame->intra_error);
   sr_decay = 1.0 - sr_diff_part - (INTRA_PART * modified_pcnt_intra);
 }
 return AOMMAX(sr_decay, DEFAULT_DECAY_LIMIT);
}

// This function gives an estimate of how badly we believe the prediction
// quality is decaying from frame to frame.
static double get_zero_motion_factor(const FIRSTPASS_STATS *frame) {
 const double zero_motion_pct = frame->pcnt_inter - frame->pcnt_motion;
 double sr_decay = get_sr_decay_rate(frame);
 return AOMMIN(sr_decay, zero_motion_pct);
}

#define DEFAULT_ZM_FACTOR 0.5
static double get_prediction_decay_rate(const FIRSTPASS_STATS *frame_stats) {
 const double sr_decay_rate = get_sr_decay_rate(frame_stats);
 double zero_motion_factor =
     DEFAULT_ZM_FACTOR * (frame_stats->pcnt_inter - frame_stats->pcnt_motion);

 // Clamp value to range 0.0 to 1.0
 // This should happen anyway if input values are sensibly clamped but checked
 // here just in case.
 if (zero_motion_factor > 1.0)
   zero_motion_factor = 1.0;
 else if (zero_motion_factor < 0.0)
   zero_motion_factor = 0.0;

 return AOMMAX(zero_motion_factor,
               (sr_decay_rate + ((1.0 - sr_decay_rate) * zero_motion_factor)));
}

// Function to test for a condition where a complex transition is followed
// by a static section. For example in slide shows where there is a fade
// between slides. This is to help with more optimal kf and gf positioning.
static int detect_transition_to_still(const FIRSTPASS_INFO *firstpass_info,
                                     int next_stats_index,
                                     const int min_gf_interval,
                                     const int frame_interval,
                                     const int still_interval,
                                     const double loop_decay_rate,
                                     const double last_decay_rate) {
 // Break clause to detect very still sections after motion
 // For example a static image after a fade or other transition
 // instead of a clean scene cut.
 if (frame_interval > min_gf_interval && loop_decay_rate >= 0.999 &&
     last_decay_rate < 0.9) {
   int stats_left =
       av1_firstpass_info_future_count(firstpass_info, next_stats_index);
   if (stats_left >= still_interval) {
     int j;
     // Look ahead a few frames to see if static condition persists...
     for (j = 0; j < still_interval; ++j) {
       const FIRSTPASS_STATS *stats =
           av1_firstpass_info_peek(firstpass_info, next_stats_index + j);
       if (stats->pcnt_inter - stats->pcnt_motion < 0.999) break;
     }
     // Only if it does do we signal a transition to still.
     return j == still_interval;
   }
 }
 return 0;
}

// This function detects a flash through the high relative pcnt_second_ref
// score in the frame following a flash frame. The offset passed in should
// reflect this.
static int detect_flash(const TWO_PASS *twopass,
                       const TWO_PASS_FRAME *twopass_frame, const int offset) {
 const FIRSTPASS_STATS *const next_frame =
     read_frame_stats(twopass, twopass_frame, offset);

 // What we are looking for here is a situation where there is a
 // brief break in prediction (such as a flash) but subsequent frames
 // are reasonably well predicted by an earlier (pre flash) frame.
 // The recovery after a flash is indicated by a high pcnt_second_ref
 // compared to pcnt_inter.
 return next_frame != NULL &&
        next_frame->pcnt_second_ref > next_frame->pcnt_inter &&
        next_frame->pcnt_second_ref >= 0.5;
}

// Update the motion related elements to the GF arf boost calculation.
static void accumulate_frame_motion_stats(const FIRSTPASS_STATS *stats,
                                         GF_GROUP_STATS *gf_stats, double f_w,
                                         double f_h) {
 const double pct = stats->pcnt_motion;

 // Accumulate Motion In/Out of frame stats.
 gf_stats->this_frame_mv_in_out = stats->mv_in_out_count * pct;
 gf_stats->mv_in_out_accumulator += gf_stats->this_frame_mv_in_out;
 gf_stats->abs_mv_in_out_accumulator += fabs(gf_stats->this_frame_mv_in_out);

 // Accumulate a measure of how uniform (or conversely how random) the motion
 // field is (a ratio of abs(mv) / mv).
 if (pct > 0.05) {
   const double mvr_ratio =
       fabs(stats->mvr_abs) / DOUBLE_DIVIDE_CHECK(fabs(stats->MVr));
   const double mvc_ratio =
       fabs(stats->mvc_abs) / DOUBLE_DIVIDE_CHECK(fabs(stats->MVc));

   gf_stats->mv_ratio_accumulator +=
       pct *
       (mvr_ratio < stats->mvr_abs * f_h ? mvr_ratio : stats->mvr_abs * f_h);
   gf_stats->mv_ratio_accumulator +=
       pct *
       (mvc_ratio < stats->mvc_abs * f_w ? mvc_ratio : stats->mvc_abs * f_w);
 }
}

static void accumulate_this_frame_stats(const FIRSTPASS_STATS *stats,
                                       const double mod_frame_err,
                                       GF_GROUP_STATS *gf_stats) {
 gf_stats->gf_group_err += mod_frame_err;
#if GROUP_ADAPTIVE_MAXQ
 gf_stats->gf_group_raw_error += stats->coded_error;
#endif
 gf_stats->gf_group_skip_pct += stats->intra_skip_pct;
 gf_stats->gf_group_inactive_zone_rows += stats->inactive_zone_rows;
}

static void accumulate_next_frame_stats(const FIRSTPASS_STATS *stats,
                                       const int flash_detected,
                                       const int frames_since_key,
                                       const int cur_idx,
                                       GF_GROUP_STATS *gf_stats, int f_w,
                                       int f_h) {
 accumulate_frame_motion_stats(stats, gf_stats, f_w, f_h);
 // sum up the metric values of current gf group
 gf_stats->avg_sr_coded_error += stats->sr_coded_error;
 gf_stats->avg_pcnt_second_ref += stats->pcnt_second_ref;
 gf_stats->avg_new_mv_count += stats->new_mv_count;
 gf_stats->avg_wavelet_energy += stats->frame_avg_wavelet_energy;
 if (fabs(stats->raw_error_stdev) > 0.000001) {
   gf_stats->non_zero_stdev_count++;
   gf_stats->avg_raw_err_stdev += stats->raw_error_stdev;
 }

 // Accumulate the effect of prediction quality decay
 if (!flash_detected) {
   gf_stats->last_loop_decay_rate = gf_stats->loop_decay_rate;
   gf_stats->loop_decay_rate = get_prediction_decay_rate(stats);

   gf_stats->decay_accumulator =
       gf_stats->decay_accumulator * gf_stats->loop_decay_rate;

   // Monitor for static sections.
   if ((frames_since_key + cur_idx - 1) > 1) {
     gf_stats->zero_motion_accumulator = AOMMIN(
         gf_stats->zero_motion_accumulator, get_zero_motion_factor(stats));
   }
 }
}

static void average_gf_stats(const int total_frame, GF_GROUP_STATS *gf_stats) {
 if (total_frame) {
   gf_stats->avg_sr_coded_error /= total_frame;
   gf_stats->avg_pcnt_second_ref /= total_frame;
   gf_stats->avg_new_mv_count /= total_frame;
   gf_stats->avg_wavelet_energy /= total_frame;
 }

 if (gf_stats->non_zero_stdev_count)
   gf_stats->avg_raw_err_stdev /= gf_stats->non_zero_stdev_count;
}

#define BOOST_FACTOR 12.5
static double baseline_err_per_mb(const FRAME_INFO *frame_info) {
 unsigned int screen_area = frame_info->frame_height * frame_info->frame_width;

 // Use a different error per mb factor for calculating boost for
 //  different formats.
 if (screen_area <= 640 * 360) {
   return 500.0;
 } else {
   return 1000.0;
 }
}

static double calc_frame_boost(const PRIMARY_RATE_CONTROL *p_rc,
                              const FRAME_INFO *frame_info,
                              const FIRSTPASS_STATS *this_frame,
                              double this_frame_mv_in_out, double max_boost) {
 double frame_boost;
 const double lq = av1_convert_qindex_to_q(p_rc->avg_frame_qindex[INTER_FRAME],
                                           frame_info->bit_depth);
 const double boost_q_correction = AOMMIN((0.5 + (lq * 0.015)), 1.5);
 const double active_area = calculate_active_area(frame_info, this_frame);

 // Underlying boost factor is based on inter error ratio.
 frame_boost = AOMMAX(baseline_err_per_mb(frame_info) * active_area,
                      this_frame->intra_error * active_area) /
               DOUBLE_DIVIDE_CHECK(this_frame->coded_error);
 frame_boost = frame_boost * BOOST_FACTOR * boost_q_correction;

 // Increase boost for frames where new data coming into frame (e.g. zoom out).
 // Slightly reduce boost if there is a net balance of motion out of the frame
 // (zoom in). The range for this_frame_mv_in_out is -1.0 to +1.0.
 if (this_frame_mv_in_out > 0.0)
   frame_boost += frame_boost * (this_frame_mv_in_out * 2.0);
 // In the extreme case the boost is halved.
 else
   frame_boost += frame_boost * (this_frame_mv_in_out / 2.0);

 return AOMMIN(frame_boost, max_boost * boost_q_correction);
}

static double calc_kf_frame_boost(const PRIMARY_RATE_CONTROL *p_rc,
                                 const FRAME_INFO *frame_info,
                                 const FIRSTPASS_STATS *this_frame,
                                 double *sr_accumulator, double max_boost) {
 double frame_boost;
 const double lq = av1_convert_qindex_to_q(p_rc->avg_frame_qindex[INTER_FRAME],
                                           frame_info->bit_depth);
 const double boost_q_correction = AOMMIN((0.50 + (lq * 0.015)), 2.00);
 const double active_area = calculate_active_area(frame_info, this_frame);

 // Underlying boost factor is based on inter error ratio.
 frame_boost = AOMMAX(baseline_err_per_mb(frame_info) * active_area,
                      this_frame->intra_error * active_area) /
               DOUBLE_DIVIDE_CHECK(
                   (this_frame->coded_error + *sr_accumulator) * active_area);

 // Update the accumulator for second ref error difference.
 // This is intended to give an indication of how much the coded error is
 // increasing over time.
 *sr_accumulator += (this_frame->sr_coded_error - this_frame->coded_error);
 *sr_accumulator = AOMMAX(0.0, *sr_accumulator);

 // Q correction and scaling
 // The 40.0 value here is an experimentally derived baseline minimum.
 // This value is in line with the minimum per frame boost in the alt_ref
 // boost calculation.
 frame_boost = ((frame_boost + 40.0) * boost_q_correction);

 return AOMMIN(frame_boost, max_boost * boost_q_correction);
}

static int get_projected_gfu_boost(const PRIMARY_RATE_CONTROL *p_rc,
                                  int gfu_boost, int frames_to_project,
                                  int num_stats_used_for_gfu_boost) {
 /*
  * If frames_to_project is equal to num_stats_used_for_gfu_boost,
  * it means that gfu_boost was calculated over frames_to_project to
  * begin with(ie; all stats required were available), hence return
  * the original boost.
  */
 if (num_stats_used_for_gfu_boost >= frames_to_project) return gfu_boost;

 double min_boost_factor = sqrt(p_rc->baseline_gf_interval);
 // Get the current tpl factor (number of frames = frames_to_project).
 double tpl_factor = av1_get_gfu_boost_projection_factor(
     min_boost_factor, MAX_GFUBOOST_FACTOR, frames_to_project);
 // Get the tpl factor when number of frames = num_stats_used_for_prior_boost.
 double tpl_factor_num_stats = av1_get_gfu_boost_projection_factor(
     min_boost_factor, MAX_GFUBOOST_FACTOR, num_stats_used_for_gfu_boost);
 int projected_gfu_boost =
     (int)rint((tpl_factor * gfu_boost) / tpl_factor_num_stats);
 return projected_gfu_boost;
}

#define GF_MAX_BOOST 90.0
#define GF_MIN_BOOST 50
#define MIN_DECAY_FACTOR 0.01
int av1_calc_arf_boost(const TWO_PASS *twopass,
                      const TWO_PASS_FRAME *twopass_frame,
                      const PRIMARY_RATE_CONTROL *p_rc, FRAME_INFO *frame_info,
                      int offset, int f_frames, int b_frames,
                      int *num_fpstats_used, int *num_fpstats_required,
                      int project_gfu_boost) {
 int i;
 GF_GROUP_STATS gf_stats;
 init_gf_stats(&gf_stats);
 double boost_score = (double)NORMAL_BOOST;
 int arf_boost;
 int flash_detected = 0;
 if (num_fpstats_used) *num_fpstats_used = 0;

 // Search forward from the proposed arf/next gf position.
 for (i = 0; i < f_frames; ++i) {
   const FIRSTPASS_STATS *this_frame =
       read_frame_stats(twopass, twopass_frame, i + offset);
   if (this_frame == NULL) break;

   // Update the motion related elements to the boost calculation.
   accumulate_frame_motion_stats(this_frame, &gf_stats,
                                 frame_info->frame_width,
                                 frame_info->frame_height);

   // We want to discount the flash frame itself and the recovery
   // frame that follows as both will have poor scores.
   flash_detected = detect_flash(twopass, twopass_frame, i + offset) ||
                    detect_flash(twopass, twopass_frame, i + offset + 1);

   // Accumulate the effect of prediction quality decay.
   if (!flash_detected) {
     gf_stats.decay_accumulator *= get_prediction_decay_rate(this_frame);
     gf_stats.decay_accumulator = gf_stats.decay_accumulator < MIN_DECAY_FACTOR
                                      ? MIN_DECAY_FACTOR
                                      : gf_stats.decay_accumulator;
   }

   boost_score +=
       gf_stats.decay_accumulator *
       calc_frame_boost(p_rc, frame_info, this_frame,
                        gf_stats.this_frame_mv_in_out, GF_MAX_BOOST);
   if (num_fpstats_used) (*num_fpstats_used)++;
 }

 arf_boost = (int)boost_score;

 // Reset for backward looking loop.
 boost_score = 0.0;
 init_gf_stats(&gf_stats);
 // Search backward towards last gf position.
 for (i = -1; i >= -b_frames; --i) {
   const FIRSTPASS_STATS *this_frame =
       read_frame_stats(twopass, twopass_frame, i + offset);
   if (this_frame == NULL) break;

   // Update the motion related elements to the boost calculation.
   accumulate_frame_motion_stats(this_frame, &gf_stats,
                                 frame_info->frame_width,
                                 frame_info->frame_height);

   // We want to discount the the flash frame itself and the recovery
   // frame that follows as both will have poor scores.
   flash_detected = detect_flash(twopass, twopass_frame, i + offset) ||
                    detect_flash(twopass, twopass_frame, i + offset + 1);

   // Cumulative effect of prediction quality decay.
   if (!flash_detected) {
     gf_stats.decay_accumulator *= get_prediction_decay_rate(this_frame);
     gf_stats.decay_accumulator = gf_stats.decay_accumulator < MIN_DECAY_FACTOR
                                      ? MIN_DECAY_FACTOR
                                      : gf_stats.decay_accumulator;
   }

   boost_score +=
       gf_stats.decay_accumulator *
       calc_frame_boost(p_rc, frame_info, this_frame,
                        gf_stats.this_frame_mv_in_out, GF_MAX_BOOST);
   if (num_fpstats_used) (*num_fpstats_used)++;
 }
 arf_boost += (int)boost_score;

 if (project_gfu_boost) {
   assert(num_fpstats_required != NULL);
   assert(num_fpstats_used != NULL);
   *num_fpstats_required = f_frames + b_frames;
   arf_boost = get_projected_gfu_boost(p_rc, arf_boost, *num_fpstats_required,
                                       *num_fpstats_used);
 }

 if (arf_boost < ((b_frames + f_frames) * GF_MIN_BOOST))
   arf_boost = ((b_frames + f_frames) * GF_MIN_BOOST);

 return arf_boost;
}

// Calculate a section intra ratio used in setting max loop filter.
static int calculate_section_intra_ratio(const FIRSTPASS_STATS *begin,
                                        const FIRSTPASS_STATS *end,
                                        int section_length) {
 const FIRSTPASS_STATS *s = begin;
 double intra_error = 0.0;
 double coded_error = 0.0;
 int i = 0;

 while (s < end && i < section_length) {
   intra_error += s->intra_error;
   coded_error += s->coded_error;
   ++s;
   ++i;
 }

 return (int)(intra_error / DOUBLE_DIVIDE_CHECK(coded_error));
}

/*!\brief Calculates the bit target for this GF/ARF group
*
* \ingroup rate_control
*
* Calculates the total bits to allocate in this GF/ARF group.
*
* \param[in]    cpi              Top-level encoder structure
* \param[in]    gf_group_err     Cumulative coded error score for the
*                                frames making up this group.
*
* \return The target total number of bits for this GF/ARF group.
*/
static int64_t calculate_total_gf_group_bits(AV1_COMP *cpi,
                                            double gf_group_err) {
 const RATE_CONTROL *const rc = &cpi->rc;
 const PRIMARY_RATE_CONTROL *const p_rc = &cpi->ppi->p_rc;
 const TWO_PASS *const twopass = &cpi->ppi->twopass;
 const int max_bits = frame_max_bits(rc, &cpi->oxcf);
 int64_t total_group_bits;

 // Calculate the bits to be allocated to the group as a whole.
 if ((twopass->kf_group_bits > 0) && (twopass->kf_group_error_left > 0)) {
   total_group_bits = (int64_t)(twopass->kf_group_bits *
                                (gf_group_err / twopass->kf_group_error_left));
 } else {
   total_group_bits = 0;
 }

 // Clamp odd edge cases.
 total_group_bits = (total_group_bits < 0) ? 0
                    : (total_group_bits > twopass->kf_group_bits)
                        ? twopass->kf_group_bits
                        : total_group_bits;

 // Clip based on user supplied data rate variability limit.
 if (total_group_bits > (int64_t)max_bits * p_rc->baseline_gf_interval)
   total_group_bits = (int64_t)max_bits * p_rc->baseline_gf_interval;

 return total_group_bits;
}

// Calculate the number of bits to assign to boosted frames in a group.
static int calculate_boost_bits(int frame_count, int boost,
                               int64_t total_group_bits) {
 int allocation_chunks;

 // return 0 for invalid inputs (could arise e.g. through rounding errors)
 if (!boost || (total_group_bits <= 0)) return 0;

 if (frame_count <= 0) return (int)(AOMMIN(total_group_bits, INT_MAX));

 allocation_chunks = (frame_count * 100) + boost;

 // Prevent overflow.
 if (boost > 1023) {
   int divisor = boost >> 10;
   boost /= divisor;
   allocation_chunks /= divisor;
 }

 // Calculate the number of extra bits for use in the boosted frame or frames.
 return AOMMAX((int)(((int64_t)boost * total_group_bits) / allocation_chunks),
               0);
}

// Calculate the boost factor based on the number of bits assigned, i.e. the
// inverse of calculate_boost_bits().
static int calculate_boost_factor(int frame_count, int bits,
                                 int64_t total_group_bits) {
 return (int)(100.0 * frame_count * bits / (total_group_bits - bits));
}

// Reduce the number of bits assigned to keyframe or arf if necessary, to
// prevent bitrate spikes that may break level constraints.
// frame_type: 0: keyframe; 1: arf.
static int adjust_boost_bits_for_target_level(const AV1_COMP *const cpi,
                                             RATE_CONTROL *const rc,
                                             int bits_assigned,
                                             int64_t group_bits,
                                             int frame_type) {
 const AV1_COMMON *const cm = &cpi->common;
 const SequenceHeader *const seq_params = cm->seq_params;
 PRIMARY_RATE_CONTROL *const p_rc = &cpi->ppi->p_rc;
 const int temporal_layer_id = cm->temporal_layer_id;
 const int spatial_layer_id = cm->spatial_layer_id;
 for (int index = 0; index < seq_params->operating_points_cnt_minus_1 + 1;
      ++index) {
   if (!is_in_operating_point(seq_params->operating_point_idc[index],
                              temporal_layer_id, spatial_layer_id)) {
     continue;
   }

   const AV1_LEVEL target_level =
       cpi->ppi->level_params.target_seq_level_idx[index];
   if (target_level >= SEQ_LEVELS) continue;

   assert(is_valid_seq_level_idx(target_level));

   const double level_bitrate_limit = av1_get_max_bitrate_for_level(
       target_level, seq_params->tier[0], seq_params->profile);
   const int target_bits_per_frame =
       (int)(level_bitrate_limit / cpi->framerate);
   if (frame_type == 0) {
     // Maximum bits for keyframe is 8 times the target_bits_per_frame.
     const int level_enforced_max_kf_bits = target_bits_per_frame * 8;
     if (bits_assigned > level_enforced_max_kf_bits) {
       const int frames = rc->frames_to_key - 1;
       p_rc->kf_boost = calculate_boost_factor(
           frames, level_enforced_max_kf_bits, group_bits);
       bits_assigned =
           calculate_boost_bits(frames, p_rc->kf_boost, group_bits);
     }
   } else if (frame_type == 1) {
     // Maximum bits for arf is 4 times the target_bits_per_frame.
     const int level_enforced_max_arf_bits = target_bits_per_frame * 4;
     if (bits_assigned > level_enforced_max_arf_bits) {
       p_rc->gfu_boost =
           calculate_boost_factor(p_rc->baseline_gf_interval,
                                  level_enforced_max_arf_bits, group_bits);
       bits_assigned = calculate_boost_bits(p_rc->baseline_gf_interval,
                                            p_rc->gfu_boost, group_bits);
     }
   } else {
     assert(0);
   }
 }

 return bits_assigned;
}

// Allocate bits to each frame in a GF / ARF group
static void allocate_gf_group_bits(GF_GROUP *gf_group,
                                  PRIMARY_RATE_CONTROL *const p_rc,
                                  RATE_CONTROL *const rc,
                                  int64_t gf_group_bits, int gf_arf_bits,
                                  int key_frame, int use_arf) {
 static const double layer_fraction[MAX_ARF_LAYERS + 1] = { 1.0,  0.70, 0.55,
                                                            0.60, 0.60, 1.0,
                                                            1.0 };
 int64_t total_group_bits = gf_group_bits;
 int base_frame_bits;
 const int gf_group_size = gf_group->size;
 int layer_frames[MAX_ARF_LAYERS + 1] = { 0 };

 // For key frames the frame target rate is already set and it
 // is also the golden frame.
 // === [frame_index == 0] ===
 int frame_index = !!key_frame;

 // Subtract the extra bits set aside for ARF frames from the Group Total
 if (use_arf) total_group_bits -= gf_arf_bits;

 int num_frames =
     AOMMAX(1, p_rc->baseline_gf_interval - (rc->frames_since_key == 0));
 base_frame_bits = (int)(total_group_bits / num_frames);

 // Check the number of frames in each layer in case we have a
 // non standard group length.
 int max_arf_layer = gf_group->max_layer_depth - 1;
 for (int idx = frame_index; idx < gf_group_size; ++idx) {
   if ((gf_group->update_type[idx] == ARF_UPDATE) ||
       (gf_group->update_type[idx] == INTNL_ARF_UPDATE)) {
     layer_frames[gf_group->layer_depth[idx]]++;
   }
 }

 // Allocate extra bits to each ARF layer
 int i;
 int layer_extra_bits[MAX_ARF_LAYERS + 1] = { 0 };
 assert(max_arf_layer <= MAX_ARF_LAYERS);
 for (i = 1; i <= max_arf_layer; ++i) {
   double fraction = (i == max_arf_layer) ? 1.0 : layer_fraction[i];
   layer_extra_bits[i] =
       (int)((gf_arf_bits * fraction) / AOMMAX(1, layer_frames[i]));
   gf_arf_bits -= (int)(gf_arf_bits * fraction);
 }

 // Now combine ARF layer and baseline bits to give total bits for each frame.
 int arf_extra_bits;
 for (int idx = frame_index; idx < gf_group_size; ++idx) {
   switch (gf_group->update_type[idx]) {
     case ARF_UPDATE:
     case INTNL_ARF_UPDATE:
       arf_extra_bits = layer_extra_bits[gf_group->layer_depth[idx]];
       gf_group->bit_allocation[idx] =
           (base_frame_bits > INT_MAX - arf_extra_bits)
               ? INT_MAX
               : (base_frame_bits + arf_extra_bits);
       break;
     case INTNL_OVERLAY_UPDATE:
     case OVERLAY_UPDATE: gf_group->bit_allocation[idx] = 0; break;
     default: gf_group->bit_allocation[idx] = base_frame_bits; break;
   }
 }

 // Set the frame following the current GOP to 0 bit allocation. For ARF
 // groups, this next frame will be overlay frame, which is the first frame
 // in the next GOP. For GF group, next GOP will overwrite the rate allocation.
 // Setting this frame to use 0 bit (of out the current GOP budget) will
 // simplify logics in reference frame management.
 if (gf_group_size < MAX_STATIC_GF_GROUP_LENGTH)
   gf_group->bit_allocation[gf_group_size] = 0;
}

// Returns true if KF group and GF group both are almost completely static.
static inline int is_almost_static(double gf_zero_motion, int kf_zero_motion,
                                  int is_lap_enabled) {
 if (is_lap_enabled) {
   /*
    * when LAP enabled kf_zero_motion is not reliable, so use strict
    * constraint on gf_zero_motion.
    */
   return (gf_zero_motion >= 0.999);
 } else {
   return (gf_zero_motion >= 0.995) &&
          (kf_zero_motion >= STATIC_KF_GROUP_THRESH);
 }
}

#define ARF_ABS_ZOOM_THRESH 4.4
static inline int detect_gf_cut(AV1_COMP *cpi, int frame_index, int cur_start,
                               int flash_detected, int active_max_gf_interval,
                               int active_min_gf_interval,
                               GF_GROUP_STATS *gf_stats) {
 RATE_CONTROL *const rc = &cpi->rc;
 TWO_PASS *const twopass = &cpi->ppi->twopass;
 AV1_COMMON *const cm = &cpi->common;
 // Motion breakout threshold for loop below depends on image size.
 const double mv_ratio_accumulator_thresh = (cm->height + cm->width) / 4.0;

 if (!flash_detected) {
   // Break clause to detect very still sections after motion. For example,
   // a static image after a fade or other transition.

   // TODO(angiebird): This is a temporary change, we will avoid using
   // twopass_frame.stats_in in the follow-up CL
   int index = (int)(cpi->twopass_frame.stats_in -
                     twopass->stats_buf_ctx->stats_in_start);
   if (detect_transition_to_still(&twopass->firstpass_info, index,
                                  rc->min_gf_interval, frame_index - cur_start,
                                  5, gf_stats->loop_decay_rate,
                                  gf_stats->last_loop_decay_rate)) {
     return 1;
   }
 }

 // Some conditions to breakout after min interval.
 if (frame_index - cur_start >= active_min_gf_interval &&
     // If possible don't break very close to a kf
     (rc->frames_to_key - frame_index >= rc->min_gf_interval) &&
     ((frame_index - cur_start) & 0x01) && !flash_detected &&
     (gf_stats->mv_ratio_accumulator > mv_ratio_accumulator_thresh ||
      gf_stats->abs_mv_in_out_accumulator > ARF_ABS_ZOOM_THRESH)) {
   return 1;
 }

 // If almost totally static, we will not use the the max GF length later,
 // so we can continue for more frames.
 if (((frame_index - cur_start) >= active_max_gf_interval + 1) &&
     !is_almost_static(gf_stats->zero_motion_accumulator,
                       twopass->kf_zeromotion_pct, cpi->ppi->lap_enabled)) {
   return 1;
 }
 return 0;
}

static int is_shorter_gf_interval_better(
   AV1_COMP *cpi, const EncodeFrameParams *frame_params) {
 const RATE_CONTROL *const rc = &cpi->rc;
 PRIMARY_RATE_CONTROL *const p_rc = &cpi->ppi->p_rc;
 int gop_length_decision_method = cpi->sf.tpl_sf.gop_length_decision_method;
 int shorten_gf_interval;

 av1_tpl_preload_rc_estimate(cpi, frame_params);

 if (gop_length_decision_method == 2) {
   // GF group length is decided based on GF boost and tpl stats of ARFs from
   // base layer, (base+1) layer.
   shorten_gf_interval =
       (p_rc->gfu_boost <
        p_rc->num_stats_used_for_gfu_boost * GF_MIN_BOOST * 1.4) &&
       !av1_tpl_setup_stats(cpi, 3, frame_params);
 } else {
   int do_complete_tpl = 1;
   GF_GROUP *const gf_group = &cpi->ppi->gf_group;
   int is_temporal_filter_enabled =
       (rc->frames_since_key > 0 && gf_group->arf_index > -1);

   if (gop_length_decision_method == 1) {
     // Check if tpl stats of ARFs from base layer, (base+1) layer,
     // (base+2) layer can decide the GF group length.
     int gop_length_eval = av1_tpl_setup_stats(cpi, 2, frame_params);

     if (gop_length_eval != 2) {
       do_complete_tpl = 0;
       shorten_gf_interval = !gop_length_eval;
     }
   }

   if (do_complete_tpl) {
     // Decide GF group length based on complete tpl stats.
     shorten_gf_interval = !av1_tpl_setup_stats(cpi, 1, frame_params);
     // Tpl stats is reused when the ARF is temporally filtered and GF
     // interval is not shortened.
     if (is_temporal_filter_enabled && !shorten_gf_interval) {
       cpi->skip_tpl_setup_stats = 1;
#if CONFIG_BITRATE_ACCURACY && !CONFIG_THREE_PASS
       assert(cpi->gf_frame_index == 0);
       av1_vbr_rc_update_q_index_list(&cpi->vbr_rc_info, &cpi->ppi->tpl_data,
                                      gf_group,
                                      cpi->common.seq_params->bit_depth);
#endif  // CONFIG_BITRATE_ACCURACY
     }
   }
 }
 return shorten_gf_interval;
}

#define MIN_SHRINK_LEN 6  // the minimum length of gf if we are shrinking
#define SMOOTH_FILT_LEN 7
#define HALF_FILT_LEN (SMOOTH_FILT_LEN / 2)
#define WINDOW_SIZE 7
#define HALF_WIN (WINDOW_SIZE / 2)

// Smooth filter intra_error and coded_error in firstpass stats.
// If stats[i].is_flash==1, the ith element should not be used in the filtering.
static void smooth_filter_stats(const FIRSTPASS_STATS *stats, int start_idx,
                               int last_idx, double *filt_intra_err,
                               double *filt_coded_err) {
 // A 7-tap gaussian smooth filter
 static const double smooth_filt[SMOOTH_FILT_LEN] = { 0.006, 0.061, 0.242,
                                                      0.383, 0.242, 0.061,
                                                      0.006 };
 int i, j;
 for (i = start_idx; i <= last_idx; i++) {
   double total_wt = 0;
   for (j = -HALF_FILT_LEN; j <= HALF_FILT_LEN; j++) {
     int idx = clamp(i + j, start_idx, last_idx);
     if (stats[idx].is_flash) continue;

     filt_intra_err[i] +=
         smooth_filt[j + HALF_FILT_LEN] * stats[idx].intra_error;
     total_wt += smooth_filt[j + HALF_FILT_LEN];
   }
   if (total_wt > 0.01) {
     filt_intra_err[i] /= total_wt;
   } else {
     filt_intra_err[i] = stats[i].intra_error;
   }
 }
 for (i = start_idx; i <= last_idx; i++) {
   double total_wt = 0;
   for (j = -HALF_FILT_LEN; j <= HALF_FILT_LEN; j++) {
     int idx = clamp(i + j, start_idx, last_idx);
     // Coded error involves idx and idx - 1.
     if (stats[idx].is_flash || (idx > 0 && stats[idx - 1].is_flash)) continue;

     filt_coded_err[i] +=
         smooth_filt[j + HALF_FILT_LEN] * stats[idx].coded_error;
     total_wt += smooth_filt[j + HALF_FILT_LEN];
   }
   if (total_wt > 0.01) {
     filt_coded_err[i] /= total_wt;
   } else {
     filt_coded_err[i] = stats[i].coded_error;
   }
 }
}

// Calculate gradient
static void get_gradient(const double *values, int start, int last,
                        double *grad) {
 if (start == last) {
   grad[start] = 0;
   return;
 }
 for (int i = start; i <= last; i++) {
   int prev = AOMMAX(i - 1, start);
   int next = AOMMIN(i + 1, last);
   grad[i] = (values[next] - values[prev]) / (next - prev);
 }
}

static int find_next_scenecut(const FIRSTPASS_STATS *const stats_start,
                             int first, int last) {
 // Identify unstable areas caused by scenecuts.
 // Find the max and 2nd max coded error, and the average of the rest frames.
 // If there is only one frame that yields a huge coded error, it is likely a
 // scenecut.
 double this_ratio, max_prev_ratio, max_next_ratio, max_prev_coded,
     max_next_coded;

 if (last - first == 0) return -1;

 for (int i = first; i <= last; i++) {
   if (stats_start[i].is_flash || (i > 0 && stats_start[i - 1].is_flash))
     continue;
   double temp_intra = AOMMAX(stats_start[i].intra_error, 0.01);
   this_ratio = stats_start[i].coded_error / temp_intra;
   // find the avg ratio in the preceding neighborhood
   max_prev_ratio = 0;
   max_prev_coded = 0;
   for (int j = AOMMAX(first, i - HALF_WIN); j < i; j++) {
     if (stats_start[j].is_flash || (j > 0 && stats_start[j - 1].is_flash))
       continue;
     temp_intra = AOMMAX(stats_start[j].intra_error, 0.01);
     double temp_ratio = stats_start[j].coded_error / temp_intra;
     if (temp_ratio > max_prev_ratio) {
       max_prev_ratio = temp_ratio;
     }
     if (stats_start[j].coded_error > max_prev_coded) {
       max_prev_coded = stats_start[j].coded_error;
     }
   }
   // find the avg ratio in the following neighborhood
   max_next_ratio = 0;
   max_next_coded = 0;
   for (int j = i + 1; j <= AOMMIN(i + HALF_WIN, last); j++) {
     if (stats_start[i].is_flash || (i > 0 && stats_start[i - 1].is_flash))
       continue;
     temp_intra = AOMMAX(stats_start[j].intra_error, 0.01);
     double temp_ratio = stats_start[j].coded_error / temp_intra;
     if (temp_ratio > max_next_ratio) {
       max_next_ratio = temp_ratio;
     }
     if (stats_start[j].coded_error > max_next_coded) {
       max_next_coded = stats_start[j].coded_error;
     }
   }

   if (max_prev_ratio < 0.001 && max_next_ratio < 0.001) {
     // the ratios are very small, only check a small fixed threshold
     if (this_ratio < 0.02) continue;
   } else {
     // check if this frame has a larger ratio than the neighborhood
     double max_sr = stats_start[i].sr_coded_error;
     if (i < last) max_sr = AOMMAX(max_sr, stats_start[i + 1].sr_coded_error);
     double max_sr_fr_ratio =
         max_sr / AOMMAX(stats_start[i].coded_error, 0.01);

     if (max_sr_fr_ratio > 1.2) continue;
     if (this_ratio < 2 * AOMMAX(max_prev_ratio, max_next_ratio) &&
         stats_start[i].coded_error <
             2 * AOMMAX(max_prev_coded, max_next_coded)) {
       continue;
     }
   }
   return i;
 }
 return -1;
}

// Remove the region with index next_region.
// parameter merge: 0: merge with previous; 1: merge with next; 2:
// merge with both, take type from previous if possible
// After removing, next_region will be the index of the next region.
static void remove_region(int merge, REGIONS *regions, int *num_regions,
                         int *next_region) {
 int k = *next_region;
 assert(k < *num_regions);
 if (*num_regions == 1) {
   *num_regions = 0;
   return;
 }
 if (k == 0) {
   merge = 1;
 } else if (k == *num_regions - 1) {
   merge = 0;
 }
 int num_merge = (merge == 2) ? 2 : 1;
 switch (merge) {
   case 0:
     regions[k - 1].last = regions[k].last;
     *next_region = k;
     break;
   case 1:
     regions[k + 1].start = regions[k].start;
     *next_region = k + 1;
     break;
   case 2:
     regions[k - 1].last = regions[k + 1].last;
     *next_region = k;
     break;
   default: assert(0);
 }
 *num_regions -= num_merge;
 for (k = *next_region - (merge == 1); k < *num_regions; k++) {
   regions[k] = regions[k + num_merge];
 }
}

// Insert a region in the cur_region_idx. The start and last should both be in
// the current region. After insertion, the cur_region_idx will point to the
// last region that was splitted from the original region.
static void insert_region(int start, int last, REGION_TYPES type,
                         REGIONS *regions, int *num_regions,
                         int *cur_region_idx) {
 int k = *cur_region_idx;
 REGION_TYPES this_region_type = regions[k].type;
 int this_region_last = regions[k].last;
 int num_add = (start != regions[k].start) + (last != regions[k].last);
 // move the following regions further to the back
 for (int r = *num_regions - 1; r > k; r--) {
   regions[r + num_add] = regions[r];
 }
 *num_regions += num_add;
 if (start > regions[k].start) {
   regions[k].last = start - 1;
   k++;
   regions[k].start = start;
 }
 regions[k].type = type;
 if (last < this_region_last) {
   regions[k].last = last;
   k++;
   regions[k].start = last + 1;
   regions[k].last = this_region_last;
   regions[k].type = this_region_type;
 } else {
   regions[k].last = this_region_last;
 }
 *cur_region_idx = k;
}

// Get the average of stats inside a region.
static void analyze_region(const FIRSTPASS_STATS *stats, int k,
                          REGIONS *regions) {
 int i;
 regions[k].avg_cor_coeff = 0;
 regions[k].avg_sr_fr_ratio = 0;
 regions[k].avg_intra_err = 0;
 regions[k].avg_coded_err = 0;

 int check_first_sr = (k != 0);

 for (i = regions[k].start; i <= regions[k].last; i++) {
   if (i > regions[k].start || check_first_sr) {
     double num_frames =
         (double)(regions[k].last - regions[k].start + check_first_sr);
     double max_coded_error =
         AOMMAX(stats[i].coded_error, stats[i - 1].coded_error);
     double this_ratio =
         stats[i].sr_coded_error / AOMMAX(max_coded_error, 0.001);
     regions[k].avg_sr_fr_ratio += this_ratio / num_frames;
   }

   regions[k].avg_intra_err +=
       stats[i].intra_error / (double)(regions[k].last - regions[k].start + 1);
   regions[k].avg_coded_err +=
       stats[i].coded_error / (double)(regions[k].last - regions[k].start + 1);

   regions[k].avg_cor_coeff +=
       AOMMAX(stats[i].cor_coeff, 0.001) /
       (double)(regions[k].last - regions[k].start + 1);
   regions[k].avg_noise_var +=
       AOMMAX(stats[i].noise_var, 0.001) /
       (double)(regions[k].last - regions[k].start + 1);
 }
}

// Calculate the regions stats of every region.
static void get_region_stats(const FIRSTPASS_STATS *stats, REGIONS *regions,
                            int num_regions) {
 for (int k = 0; k < num_regions; k++) {
   analyze_region(stats, k, regions);
 }
}

// Find tentative stable regions
static int find_stable_regions(const FIRSTPASS_STATS *stats,
                              const double *grad_coded, int this_start,
                              int this_last, REGIONS *regions) {
 int i, j, k = 0;
 regions[k].start = this_start;
 for (i = this_start; i <= this_last; i++) {
   // Check mean and variance of stats in a window
   double mean_intra = 0.001, var_intra = 0.001;
   double mean_coded = 0.001, var_coded = 0.001;
   int count = 0;
   for (j = -HALF_WIN; j <= HALF_WIN; j++) {
     int idx = clamp(i + j, this_start, this_last);
     if (stats[idx].is_flash || (idx > 0 && stats[idx - 1].is_flash)) continue;
     mean_intra += stats[idx].intra_error;
     var_intra += stats[idx].intra_error * stats[idx].intra_error;
     mean_coded += stats[idx].coded_error;
     var_coded += stats[idx].coded_error * stats[idx].coded_error;
     count++;
   }

   REGION_TYPES cur_type;
   if (count > 0) {
     mean_intra /= (double)count;
     var_intra /= (double)count;
     mean_coded /= (double)count;
     var_coded /= (double)count;
     int is_intra_stable = (var_intra / (mean_intra * mean_intra) < 1.03);
     int is_coded_stable = (var_coded / (mean_coded * mean_coded) < 1.04 &&
                            fabs(grad_coded[i]) / mean_coded < 0.05) ||
                           mean_coded / mean_intra < 0.05;
     int is_coded_small = mean_coded < 0.5 * mean_intra;
     cur_type = (is_intra_stable && is_coded_stable && is_coded_small)
                    ? STABLE_REGION
                    : HIGH_VAR_REGION;
   } else {
     cur_type = HIGH_VAR_REGION;
   }

   // mark a new region if type changes
   if (i == regions[k].start) {
     // first frame in the region
     regions[k].type = cur_type;
   } else if (cur_type != regions[k].type) {
     // Append a new region
     regions[k].last = i - 1;
     regions[k + 1].start = i;
     regions[k + 1].type = cur_type;
     k++;
   }
 }
 regions[k].last = this_last;
 return k + 1;
}

// Clean up regions that should be removed or merged.
static void cleanup_regions(REGIONS *regions, int *num_regions) {
 int k = 0;
 while (k < *num_regions) {
   if ((k > 0 && regions[k - 1].type == regions[k].type &&
        regions[k].type != SCENECUT_REGION) ||
       regions[k].last < regions[k].start) {
     remove_region(0, regions, num_regions, &k);
   } else {
     k++;
   }
 }
}

// Remove regions that are of type and shorter than length.
// Merge it with its neighboring regions.
static void remove_short_regions(REGIONS *regions, int *num_regions,
                                REGION_TYPES type, int length) {
 int k = 0;
 while (k < *num_regions && (*num_regions) > 1) {
   if ((regions[k].last - regions[k].start + 1 < length &&
        regions[k].type == type)) {
     // merge current region with the previous and next regions
     remove_region(2, regions, num_regions, &k);
   } else {
     k++;
   }
 }
 cleanup_regions(regions, num_regions);
}

static void adjust_unstable_region_bounds(const FIRSTPASS_STATS *stats,
                                         REGIONS *regions, int *num_regions) {
 int i, j, k;
 // Remove regions that are too short. Likely noise.
 remove_short_regions(regions, num_regions, STABLE_REGION, HALF_WIN);
 remove_short_regions(regions, num_regions, HIGH_VAR_REGION, HALF_WIN);

 get_region_stats(stats, regions, *num_regions);

 // Adjust region boundaries. The thresholds are empirically obtained, but
 // overall the performance is not very sensitive to small changes to them.
 for (k = 0; k < *num_regions; k++) {
   if (regions[k].type == STABLE_REGION) continue;
   if (k > 0) {
     // Adjust previous boundary.
     // First find the average intra/coded error in the previous
     // neighborhood.
     double avg_intra_err = 0;
     const int starti = AOMMAX(regions[k - 1].last - WINDOW_SIZE + 1,
                               regions[k - 1].start + 1);
     const int lasti = regions[k - 1].last;
     int counti = 0;
     for (i = starti; i <= lasti; i++) {
       avg_intra_err += stats[i].intra_error;
       counti++;
     }
     if (counti > 0) {
       avg_intra_err = AOMMAX(avg_intra_err / (double)counti, 0.001);
       int count_coded = 0, count_grad = 0;
       for (j = lasti + 1; j <= regions[k].last; j++) {
         const int intra_close =
             fabs(stats[j].intra_error - avg_intra_err) / avg_intra_err < 0.1;
         const int coded_small = stats[j].coded_error / avg_intra_err < 0.1;
         const int coeff_close = stats[j].cor_coeff > 0.995;
         if (!coeff_close || !coded_small) count_coded--;
         if (intra_close && count_coded >= 0 && count_grad >= 0) {
           // this frame probably belongs to the previous stable region
           regions[k - 1].last = j;
           regions[k].start = j + 1;
         } else {
           break;
         }
       }
     }
   }  // if k > 0
   if (k < *num_regions - 1) {
     // Adjust next boundary.
     // First find the average intra/coded error in the next neighborhood.
     double avg_intra_err = 0;
     const int starti = regions[k + 1].start;
     const int lasti = AOMMIN(regions[k + 1].last - 1,
                              regions[k + 1].start + WINDOW_SIZE - 1);
     int counti = 0;
     for (i = starti; i <= lasti; i++) {
       avg_intra_err += stats[i].intra_error;
       counti++;
     }
     if (counti > 0) {
       avg_intra_err = AOMMAX(avg_intra_err / (double)counti, 0.001);
       // At the boundary, coded error is large, but still the frame is stable
       int count_coded = 1, count_grad = 1;
       for (j = starti - 1; j >= regions[k].start; j--) {
         const int intra_close =
             fabs(stats[j].intra_error - avg_intra_err) / avg_intra_err < 0.1;
         const int coded_small =
             stats[j + 1].coded_error / avg_intra_err < 0.1;
         const int coeff_close = stats[j].cor_coeff > 0.995;
         if (!coeff_close || !coded_small) count_coded--;
         if (intra_close && count_coded >= 0 && count_grad >= 0) {
           // this frame probably belongs to the next stable region
           regions[k + 1].start = j;
           regions[k].last = j - 1;
         } else {
           break;
         }
       }
     }
   }  // if k < *num_regions - 1
 }  // end of loop over all regions

 cleanup_regions(regions, num_regions);
 remove_short_regions(regions, num_regions, HIGH_VAR_REGION, HALF_WIN);
 get_region_stats(stats, regions, *num_regions);

 // If a stable regions has higher error than neighboring high var regions,
 // or if the stable region has a lower average correlation,
 // then it should be merged with them
 k = 0;
 while (k < *num_regions && (*num_regions) > 1) {
   if (regions[k].type == STABLE_REGION &&
       (regions[k].last - regions[k].start + 1) < 2 * WINDOW_SIZE &&
       ((k > 0 &&  // previous regions
         (regions[k].avg_coded_err > regions[k - 1].avg_coded_err * 1.01 ||
          regions[k].avg_cor_coeff < regions[k - 1].avg_cor_coeff * 0.999)) &&
        (k < *num_regions - 1 &&  // next region
         (regions[k].avg_coded_err > regions[k + 1].avg_coded_err * 1.01 ||
          regions[k].avg_cor_coeff < regions[k + 1].avg_cor_coeff * 0.999)))) {
     // merge current region with the previous and next regions
     remove_region(2, regions, num_regions, &k);
     analyze_region(stats, k - 1, regions);
   } else if (regions[k].type == HIGH_VAR_REGION &&
              (regions[k].last - regions[k].start + 1) < 2 * WINDOW_SIZE &&
              ((k > 0 &&  // previous regions
                (regions[k].avg_coded_err <
                     regions[k - 1].avg_coded_err * 0.99 ||
                 regions[k].avg_cor_coeff >
                     regions[k - 1].avg_cor_coeff * 1.001)) &&
               (k < *num_regions - 1 &&  // next region
                (regions[k].avg_coded_err <
                     regions[k + 1].avg_coded_err * 0.99 ||
                 regions[k].avg_cor_coeff >
                     regions[k + 1].avg_cor_coeff * 1.001)))) {
     // merge current region with the previous and next regions
     remove_region(2, regions, num_regions, &k);
     analyze_region(stats, k - 1, regions);
   } else {
     k++;
   }
 }

 remove_short_regions(regions, num_regions, STABLE_REGION, WINDOW_SIZE);
 remove_short_regions(regions, num_regions, HIGH_VAR_REGION, HALF_WIN);
}

// Identify blending regions.
static void find_blending_regions(const FIRSTPASS_STATS *stats,
                                 REGIONS *regions, int *num_regions) {
 int i, k = 0;
 // Blending regions will have large content change, therefore will have a
 // large consistent change in intra error.
 int count_stable = 0;
 while (k < *num_regions) {
   if (regions[k].type == STABLE_REGION) {
     k++;
     count_stable++;
     continue;
   }
   int dir = 0;
   int start = 0, last;
   for (i = regions[k].start; i <= regions[k].last; i++) {
     // First mark the regions that has consistent large change of intra error.
     if (k == 0 && i == regions[k].start) continue;
     if (stats[i].is_flash || (i > 0 && stats[i - 1].is_flash)) continue;
     double grad = stats[i].intra_error - stats[i - 1].intra_error;
     int large_change = fabs(grad) / AOMMAX(stats[i].intra_error, 0.01) > 0.05;
     int this_dir = 0;
     if (large_change) {
       this_dir = (grad > 0) ? 1 : -1;
     }
     // the current trend continues
     if (dir == this_dir) continue;
     if (dir != 0) {
       // Mark the end of a new large change group and add it
       last = i - 1;
       insert_region(start, last, BLENDING_REGION, regions, num_regions, &k);
     }
     dir = this_dir;
     if (k == 0 && i == regions[k].start + 1) {
       start = i - 1;
     } else {
       start = i;
     }
   }
   if (dir != 0) {
     last = regions[k].last;
     insert_region(start, last, BLENDING_REGION, regions, num_regions, &k);
   }
   k++;
 }

 // If the blending region has very low correlation, mark it as high variance
 // since we probably cannot benefit from it anyways.
 get_region_stats(stats, regions, *num_regions);
 for (k = 0; k < *num_regions; k++) {
   if (regions[k].type != BLENDING_REGION) continue;
   if (regions[k].last == regions[k].start || regions[k].avg_cor_coeff < 0.6 ||
       count_stable == 0)
     regions[k].type = HIGH_VAR_REGION;
 }
 get_region_stats(stats, regions, *num_regions);

 // It is possible for blending to result in a "dip" in intra error (first
 // decrease then increase). Therefore we need to find the dip and combine the
 // two regions.
 k = 1;
 while (k < *num_regions) {
   if (k < *num_regions - 1 && regions[k].type == HIGH_VAR_REGION) {
     // Check if this short high variance regions is actually in the middle of
     // a blending region.
     if (regions[k - 1].type == BLENDING_REGION &&
         regions[k + 1].type == BLENDING_REGION &&
         regions[k].last - regions[k].start < 3) {
       int prev_dir = (stats[regions[k - 1].last].intra_error -
                       stats[regions[k - 1].last - 1].intra_error) > 0
                          ? 1
                          : -1;
       int next_dir = (stats[regions[k + 1].last].intra_error -
                       stats[regions[k + 1].last - 1].intra_error) > 0
                          ? 1
                          : -1;
       if (prev_dir < 0 && next_dir > 0) {
         // This is possibly a mid region of blending. Check the ratios
         double ratio_thres = AOMMIN(regions[k - 1].avg_sr_fr_ratio,
                                     regions[k + 1].avg_sr_fr_ratio) *
                              0.95;
         if (regions[k].avg_sr_fr_ratio > ratio_thres) {
           regions[k].type = BLENDING_REGION;
           remove_region(2, regions, num_regions, &k);
           analyze_region(stats, k - 1, regions);
           continue;
         }
       }
     }
   }
   // Check if we have a pair of consecutive blending regions.
   if (regions[k - 1].type == BLENDING_REGION &&
       regions[k].type == BLENDING_REGION) {
     int prev_dir = (stats[regions[k - 1].last].intra_error -
                     stats[regions[k - 1].last - 1].intra_error) > 0
                        ? 1
                        : -1;
     int next_dir = (stats[regions[k].last].intra_error -
                     stats[regions[k].last - 1].intra_error) > 0
                        ? 1
                        : -1;

     // if both are too short, no need to check
     int total_length = regions[k].last - regions[k - 1].start + 1;
     if (total_length < 4) {
       regions[k - 1].type = HIGH_VAR_REGION;
       k++;
       continue;
     }

     int to_merge = 0;
     if (prev_dir < 0 && next_dir > 0) {
       // In this case we check the last frame in the previous region.
       double prev_length =
           (double)(regions[k - 1].last - regions[k - 1].start + 1);
       double last_ratio, ratio_thres;
       if (prev_length < 2.01) {
         // if the previous region is very short
         double max_coded_error =
             AOMMAX(stats[regions[k - 1].last].coded_error,
                    stats[regions[k - 1].last - 1].coded_error);
         last_ratio = stats[regions[k - 1].last].sr_coded_error /
                      AOMMAX(max_coded_error, 0.001);
         ratio_thres = regions[k].avg_sr_fr_ratio * 0.95;
       } else {
         double max_coded_error =
             AOMMAX(stats[regions[k - 1].last].coded_error,
                    stats[regions[k - 1].last - 1].coded_error);
         last_ratio = stats[regions[k - 1].last].sr_coded_error /
                      AOMMAX(max_coded_error, 0.001);
         double prev_ratio =
             (regions[k - 1].avg_sr_fr_ratio * prev_length - last_ratio) /
             (prev_length - 1.0);
         ratio_thres = AOMMIN(prev_ratio, regions[k].avg_sr_fr_ratio) * 0.95;
       }
       if (last_ratio > ratio_thres) {
         to_merge = 1;
       }
     }

     if (to_merge) {
       remove_region(0, regions, num_regions, &k);
       analyze_region(stats, k - 1, regions);
       continue;
     } else {
       // These are possibly two separate blending regions. Mark the boundary
       // frame as HIGH_VAR_REGION to separate the two.
       int prev_k = k - 1;
       insert_region(regions[prev_k].last, regions[prev_k].last,
                     HIGH_VAR_REGION, regions, num_regions, &prev_k);
       analyze_region(stats, prev_k, regions);
       k = prev_k + 1;
       analyze_region(stats, k, regions);
     }
   }
   k++;
 }
 cleanup_regions(regions, num_regions);
}

// Clean up decision for blendings. Remove blending regions that are too short.
// Also if a very short high var region is between a blending and a stable
// region, just merge it with one of them.
static void cleanup_blendings(REGIONS *regions, int *num_regions) {
 int k = 0;
 while (k < (*num_regions) && (*num_regions) > 1) {
   int is_short_blending = regions[k].type == BLENDING_REGION &&
                           regions[k].last - regions[k].start + 1 < 5;
   int is_short_hv = regions[k].type == HIGH_VAR_REGION &&
                     regions[k].last - regions[k].start + 1 < 5;
   int has_stable_neighbor =
       ((k > 0 && regions[k - 1].type == STABLE_REGION) ||
        (k < *num_regions - 1 && regions[k + 1].type == STABLE_REGION));
   int has_blend_neighbor =
       ((k > 0 && regions[k - 1].type == BLENDING_REGION) ||
        (k < *num_regions - 1 && regions[k + 1].type == BLENDING_REGION));
   int total_neighbors = (k > 0) + (k < *num_regions - 1);

   if (is_short_blending ||
       (is_short_hv &&
        has_stable_neighbor + has_blend_neighbor >= total_neighbors)) {
     // Remove this region.Try to determine whether to combine it with the
     // previous or next region.
     int merge;
     double prev_diff =
         (k > 0)
             ? fabs(regions[k].avg_cor_coeff - regions[k - 1].avg_cor_coeff)
             : 1;
     double next_diff =
         (k < *num_regions - 1)
             ? fabs(regions[k].avg_cor_coeff - regions[k + 1].avg_cor_coeff)
             : 1;
     // merge == 0 means to merge with previous, 1 means to merge with next
     merge = prev_diff > next_diff;
     remove_region(merge, regions, num_regions, &k);
   } else {
     k++;
   }
 }
 cleanup_regions(regions, num_regions);
}

static void free_firstpass_stats_buffers(REGIONS *temp_regions,
                                        double *filt_intra_err,
                                        double *filt_coded_err,
                                        double *grad_coded) {
 aom_free(temp_regions);
 aom_free(filt_intra_err);
 aom_free(filt_coded_err);
 aom_free(grad_coded);
}

// Identify stable and unstable regions from first pass stats.
// stats_start points to the first frame to analyze.
// |offset| is the offset from the current frame to the frame stats_start is
// pointing to.
// Returns 0 on success, -1 on memory allocation failure.
static int identify_regions(const FIRSTPASS_STATS *const stats_start,
                           int total_frames, int offset, REGIONS *regions,
                           int *total_regions) {
 int k;
 if (total_frames <= 1) return 0;

 // store the initial decisions
 REGIONS *temp_regions =
     (REGIONS *)aom_malloc(total_frames * sizeof(temp_regions[0]));
 // buffers for filtered stats
 double *filt_intra_err =
     (double *)aom_calloc(total_frames, sizeof(*filt_intra_err));
 double *filt_coded_err =
     (double *)aom_calloc(total_frames, sizeof(*filt_coded_err));
 double *grad_coded = (double *)aom_calloc(total_frames, sizeof(*grad_coded));
 if (!(temp_regions && filt_intra_err && filt_coded_err && grad_coded)) {
   free_firstpass_stats_buffers(temp_regions, filt_intra_err, filt_coded_err,
                                grad_coded);
   return -1;
 }
 av1_zero_array(temp_regions, total_frames);

 int cur_region = 0, this_start = 0, this_last;

 int next_scenecut = -1;
 do {
   // first get the obvious scenecuts
   next_scenecut =
       find_next_scenecut(stats_start, this_start, total_frames - 1);
   this_last = (next_scenecut >= 0) ? (next_scenecut - 1) : total_frames - 1;

   // low-pass filter the needed stats
   smooth_filter_stats(stats_start, this_start, this_last, filt_intra_err,
                       filt_coded_err);
   get_gradient(filt_coded_err, this_start, this_last, grad_coded);

   // find tentative stable regions and unstable regions
   int num_regions = find_stable_regions(stats_start, grad_coded, this_start,
                                         this_last, temp_regions);

   adjust_unstable_region_bounds(stats_start, temp_regions, &num_regions);

   get_region_stats(stats_start, temp_regions, num_regions);

   // Try to identify blending regions in the unstable regions
   find_blending_regions(stats_start, temp_regions, &num_regions);
   cleanup_blendings(temp_regions, &num_regions);

   // The flash points should all be considered high variance points
   k = 0;
   while (k < num_regions) {
     if (temp_regions[k].type != STABLE_REGION) {
       k++;
       continue;
     }
     int start = temp_regions[k].start;
     int last = temp_regions[k].last;
     for (int i = start; i <= last; i++) {
       if (stats_start[i].is_flash) {
         insert_region(i, i, HIGH_VAR_REGION, temp_regions, &num_regions, &k);
       }
     }
     k++;
   }
   cleanup_regions(temp_regions, &num_regions);

   // copy the regions in the scenecut group
   for (k = 0; k < num_regions; k++) {
     if (temp_regions[k].last < temp_regions[k].start &&
         k == num_regions - 1) {
       num_regions--;
       break;
     }
     regions[k + cur_region] = temp_regions[k];
   }
   cur_region += num_regions;

   // add the scenecut region
   if (next_scenecut > -1) {
     // add the scenecut region, and find the next scenecut
     regions[cur_region].type = SCENECUT_REGION;
     regions[cur_region].start = next_scenecut;
     regions[cur_region].last = next_scenecut;
     cur_region++;
     this_start = next_scenecut + 1;
   }
 } while (next_scenecut >= 0);

 *total_regions = cur_region;
 get_region_stats(stats_start, regions, *total_regions);

 for (k = 0; k < *total_regions; k++) {
   // If scenecuts are very minor, mark them as high variance.
   if (regions[k].type != SCENECUT_REGION ||
       regions[k].avg_cor_coeff *
               (1 - stats_start[regions[k].start].noise_var /
                        regions[k].avg_intra_err) <
           0.8) {
     continue;
   }
   regions[k].type = HIGH_VAR_REGION;
 }
 cleanup_regions(regions, total_regions);
 get_region_stats(stats_start, regions, *total_regions);

 for (k = 0; k < *total_regions; k++) {
   regions[k].start += offset;
   regions[k].last += offset;
 }

 free_firstpass_stats_buffers(temp_regions, filt_intra_err, filt_coded_err,
                              grad_coded);
 return 0;
}

static int find_regions_index(const REGIONS *regions, int num_regions,
                             int frame_idx) {
 for (int k = 0; k < num_regions; k++) {
   if (regions[k].start <= frame_idx && regions[k].last >= frame_idx) {
     return k;
   }
 }
 return -1;
}

/*!\brief Determine the length of future GF groups.
*
* \ingroup gf_group_algo
* This function decides the gf group length of future frames in batch
*
* \param[in]    cpi              Top-level encoder structure
* \param[in]    max_gop_length   Maximum length of the GF group
* \param[in]    max_intervals    Maximum number of intervals to decide
*
* \remark Nothing is returned. Instead, cpi->ppi->rc.gf_intervals is
* changed to store the decided GF group lengths.
*/
static void calculate_gf_length(AV1_COMP *cpi, int max_gop_length,
                               int max_intervals) {
 RATE_CONTROL *const rc = &cpi->rc;
 PRIMARY_RATE_CONTROL *const p_rc = &cpi->ppi->p_rc;
 TWO_PASS *const twopass = &cpi->ppi->twopass;
 FIRSTPASS_STATS next_frame;
 const FIRSTPASS_STATS *const start_pos = cpi->twopass_frame.stats_in;
 const FIRSTPASS_STATS *const stats = start_pos - (rc->frames_since_key == 0);

 const int f_w = cpi->common.width;
 const int f_h = cpi->common.height;
 int i;

 int flash_detected;

 av1_zero(next_frame);

 if (has_no_stats_stage(cpi)) {
   for (i = 0; i < MAX_NUM_GF_INTERVALS; i++) {
     p_rc->gf_intervals[i] = AOMMIN(rc->max_gf_interval, max_gop_length);
   }
   p_rc->cur_gf_index = 0;
   rc->intervals_till_gf_calculate_due = MAX_NUM_GF_INTERVALS;
   return;
 }

 // TODO(urvang): Try logic to vary min and max interval based on q.
 const int active_min_gf_interval = rc->min_gf_interval;
 const int active_max_gf_interval =
     AOMMIN(rc->max_gf_interval, max_gop_length);
 const int min_shrink_int = AOMMAX(MIN_SHRINK_LEN, active_min_gf_interval);

 i = (rc->frames_since_key == 0);
 max_intervals = cpi->ppi->lap_enabled ? 1 : max_intervals;
 int count_cuts = 1;
 // If cpi->gf_state.arf_gf_boost_lst is 0, we are starting with a KF or GF.
 int cur_start = -1 + !cpi->ppi->gf_state.arf_gf_boost_lst, cur_last;
 int cut_pos[MAX_NUM_GF_INTERVALS + 1] = { -1 };
 int cut_here;
 GF_GROUP_STATS gf_stats;
 init_gf_stats(&gf_stats);
 while (count_cuts < max_intervals + 1) {
   // reaches next key frame, break here
   if (i >= rc->frames_to_key) {
     cut_here = 2;
   } else if (i - cur_start >= rc->static_scene_max_gf_interval) {
     // reached maximum len, but nothing special yet (almost static)
     // let's look at the next interval
     cut_here = 1;
   } else if (EOF == input_stats(twopass, &cpi->twopass_frame, &next_frame)) {
     // reaches last frame, break
     cut_here = 2;
   } else {
     // Test for the case where there is a brief flash but the prediction
     // quality back to an earlier frame is then restored.
     flash_detected = detect_flash(twopass, &cpi->twopass_frame, 0);
     // TODO(bohanli): remove redundant accumulations here, or unify
     // this and the ones in define_gf_group
     accumulate_next_frame_stats(&next_frame, flash_detected,
                                 rc->frames_since_key, i, &gf_stats, f_w, f_h);

     cut_here = detect_gf_cut(cpi, i, cur_start, flash_detected,
                              active_max_gf_interval, active_min_gf_interval,
                              &gf_stats);
   }
   if (cut_here) {
     cur_last = i - 1;  // the current last frame in the gf group
     int ori_last = cur_last;
     // The region frame idx does not start from the same frame as cur_start
     // and cur_last. Need to offset them.
     int offset = rc->frames_since_key - p_rc->regions_offset;
     REGIONS *regions = p_rc->regions;
     int num_regions = p_rc->num_regions;

     int scenecut_idx = -1;
     // only try shrinking if interval smaller than active_max_gf_interval
     if (cur_last - cur_start <= active_max_gf_interval &&
         cur_last > cur_start) {
       // find the region indices of where the first and last frame belong.
       int k_start =
           find_regions_index(regions, num_regions, cur_start + offset);
       int k_last =
           find_regions_index(regions, num_regions, cur_last + offset);
       if (cur_start + offset == 0) k_start = 0;

       // See if we have a scenecut in between
       for (int r = k_start + 1; r <= k_last; r++) {
         if (regions[r].type == SCENECUT_REGION &&
             regions[r].last - offset - cur_start > active_min_gf_interval) {
           scenecut_idx = r;
           break;
         }
       }

       // if the found scenecut is very close to the end, ignore it.
       if (regions[num_regions - 1].last - regions[scenecut_idx].last < 4) {
         scenecut_idx = -1;
       }

       if (scenecut_idx != -1) {
         // If we have a scenecut, then stop at it.
         // TODO(bohanli): add logic here to stop before the scenecut and for
         // the next gop start from the scenecut with GF
         int is_minor_sc =
             (regions[scenecut_idx].avg_cor_coeff *
                  (1 - stats[regions[scenecut_idx].start - offset].noise_var /
                           regions[scenecut_idx].avg_intra_err) >
              0.6);
         cur_last = regions[scenecut_idx].last - offset - !is_minor_sc;
       } else {
         int is_last_analysed = (k_last == num_regions - 1) &&
                                (cur_last + offset == regions[k_last].last);
         int not_enough_regions =
             k_last - k_start <=
             1 + (regions[k_start].type == SCENECUT_REGION);
         // if we are very close to the end, then do not shrink since it may
         // introduce intervals that are too short
         if (!(is_last_analysed && not_enough_regions)) {
           const double arf_length_factor = 0.1;
           double best_score = 0;
           int best_j = -1;
           const int first_frame = regions[0].start - offset;
           const int last_frame = regions[num_regions - 1].last - offset;
           // score of how much the arf helps the whole GOP
           double base_score = 0.0;
           // Accumulate base_score in
           for (int j = cur_start + 1; j < cur_start + min_shrink_int; j++) {
             if (stats + j >= twopass->stats_buf_ctx->stats_in_end) break;
             base_score = (base_score + 1.0) * stats[j].cor_coeff;
           }
           int met_blending = 0;   // Whether we have met blending areas before
           int last_blending = 0;  // Whether the previous frame if blending
           for (int j = cur_start + min_shrink_int; j <= cur_last; j++) {
             if (stats + j >= twopass->stats_buf_ctx->stats_in_end) break;
             base_score = (base_score + 1.0) * stats[j].cor_coeff;
             int this_reg =
                 find_regions_index(regions, num_regions, j + offset);
             if (this_reg < 0) continue;
             // A GOP should include at most 1 blending region.
             if (regions[this_reg].type == BLENDING_REGION) {
               last_blending = 1;
               if (met_blending) {
                 break;
               } else {
                 base_score = 0;
                 continue;
               }
             } else {
               if (last_blending) met_blending = 1;
               last_blending = 0;
             }

             // Add the factor of how good the neighborhood is for this
             // candidate arf.
             double this_score = arf_length_factor * base_score;
             double temp_accu_coeff = 1.0;
             // following frames
             int count_f = 0;
             for (int n = j + 1; n <= j + 3 && n <= last_frame; n++) {
               if (stats + n >= twopass->stats_buf_ctx->stats_in_end) break;
               temp_accu_coeff *= stats[n].cor_coeff;
               this_score +=
                   temp_accu_coeff *
                   sqrt(AOMMAX(0.5,
                               1 - stats[n].noise_var /
                                       AOMMAX(stats[n].intra_error, 0.001)));
               count_f++;
             }
             // preceding frames
             temp_accu_coeff = 1.0;
             for (int n = j; n > j - 3 * 2 + count_f && n > first_frame; n--) {
               if (stats + n < twopass->stats_buf_ctx->stats_in_start) break;
               temp_accu_coeff *= stats[n].cor_coeff;
               this_score +=
                   temp_accu_coeff *
                   sqrt(AOMMAX(0.5,
                               1 - stats[n].noise_var /
                                       AOMMAX(stats[n].intra_error, 0.001)));
             }

             if (this_score > best_score) {
               best_score = this_score;
               best_j = j;
             }
           }

           // For blending areas, move one more frame in case we missed the
           // first blending frame.
           int best_reg =
               find_regions_index(regions, num_regions, best_j + offset);
           if (best_reg < num_regions - 1 && best_reg > 0) {
             if (regions[best_reg - 1].type == BLENDING_REGION &&
                 regions[best_reg + 1].type == BLENDING_REGION) {
               if (best_j + offset == regions[best_reg].start &&
                   best_j + offset < regions[best_reg].last) {
                 best_j += 1;
               } else if (best_j + offset == regions[best_reg].last &&
                          best_j + offset > regions[best_reg].start) {
                 best_j -= 1;
               }
             }
           }

           if (cur_last - best_j < 2) best_j = cur_last;
           if (best_j > 0 && best_score > 0.1) cur_last = best_j;
           // if cannot find anything, just cut at the original place.
         }
       }
     }
     cut_pos[count_cuts] = cur_last;
     count_cuts++;

     // reset pointers to the shrunken location
     cpi->twopass_frame.stats_in = start_pos + cur_last;
     cur_start = cur_last;
     int cur_region_idx =
         find_regions_index(regions, num_regions, cur_start + 1 + offset);
     if (cur_region_idx >= 0)
       if (regions[cur_region_idx].type == SCENECUT_REGION) cur_start++;

     i = cur_last;

     if (cut_here > 1 && cur_last == ori_last) break;

     // reset accumulators
     init_gf_stats(&gf_stats);
   }
   ++i;
 }

 // save intervals
 rc->intervals_till_gf_calculate_due = count_cuts - 1;
 for (int n = 1; n < count_cuts; n++) {
   p_rc->gf_intervals[n - 1] = cut_pos[n] - cut_pos[n - 1];
 }
 p_rc->cur_gf_index = 0;
 cpi->twopass_frame.stats_in = start_pos;
}

static void correct_frames_to_key(AV1_COMP *cpi) {
 int lookahead_size =
     av1_lookahead_depth(cpi->ppi->lookahead, cpi->compressor_stage);
 if (lookahead_size <
     av1_lookahead_pop_sz(cpi->ppi->lookahead, cpi->compressor_stage)) {
   assert(
       IMPLIES(cpi->oxcf.pass != AOM_RC_ONE_PASS && cpi->ppi->frames_left > 0,
               lookahead_size == cpi->ppi->frames_left));
   cpi->rc.frames_to_key = AOMMIN(cpi->rc.frames_to_key, lookahead_size);
 } else if (cpi->ppi->frames_left > 0) {
   // Correct frames to key based on limit
   cpi->rc.frames_to_key =
       AOMMIN(cpi->rc.frames_to_key, cpi->ppi->frames_left);
 }
}

/*!\brief Define a GF group in one pass mode when no look ahead stats are
* available.
*
* \ingroup gf_group_algo
* This function defines the structure of a GF group, along with various
* parameters regarding bit-allocation and quality setup in the special
* case of one pass encoding where no lookahead stats are avialable.
*
* \param[in]    cpi             Top-level encoder structure
*
* \remark Nothing is returned. Instead, cpi->ppi->gf_group is changed.
*/
static void define_gf_group_pass0(AV1_COMP *cpi) {
 RATE_CONTROL *const rc = &cpi->rc;
 PRIMARY_RATE_CONTROL *const p_rc = &cpi->ppi->p_rc;
 GF_GROUP *const gf_group = &cpi->ppi->gf_group;
 const AV1EncoderConfig *const oxcf = &cpi->oxcf;
 const GFConfig *const gf_cfg = &oxcf->gf_cfg;
 int target;

 if (oxcf->q_cfg.aq_mode == CYCLIC_REFRESH_AQ) {
   av1_cyclic_refresh_set_golden_update(cpi);
 } else {
   p_rc->baseline_gf_interval = p_rc->gf_intervals[p_rc->cur_gf_index];
   rc->intervals_till_gf_calculate_due--;
   p_rc->cur_gf_index++;
 }

 // correct frames_to_key when lookahead queue is flushing
 correct_frames_to_key(cpi);

 if (p_rc->baseline_gf_interval > rc->frames_to_key)
   p_rc->baseline_gf_interval = rc->frames_to_key;

 p_rc->gfu_boost = DEFAULT_GF_BOOST;
 p_rc->constrained_gf_group =
     (p_rc->baseline_gf_interval >= rc->frames_to_key) ? 1 : 0;

 gf_group->max_layer_depth_allowed = oxcf->gf_cfg.gf_max_pyr_height;

 // Rare case when the look-ahead is less than the target GOP length, can't
 // generate ARF frame.
 if (p_rc->baseline_gf_interval > gf_cfg->lag_in_frames ||
     !is_altref_enabled(gf_cfg->lag_in_frames, gf_cfg->enable_auto_arf) ||
     p_rc->baseline_gf_interval < rc->min_gf_interval)
   gf_group->max_layer_depth_allowed = 0;

 // Set up the structure of this Group-Of-Pictures (same as GF_GROUP)
 av1_gop_setup_structure(cpi);

 // Allocate bits to each of the frames in the GF group.
 // TODO(sarahparker) Extend this to work with pyramid structure.
 for (int cur_index = 0; cur_index < gf_group->size; ++cur_index) {
   const FRAME_UPDATE_TYPE cur_update_type = gf_group->update_type[cur_index];
   if (oxcf->rc_cfg.mode == AOM_CBR) {
     if (cur_update_type == KF_UPDATE) {
       target = av1_calc_iframe_target_size_one_pass_cbr(cpi);
     } else {
       target = av1_calc_pframe_target_size_one_pass_cbr(cpi, cur_update_type);
     }
   } else {
     if (cur_update_type == KF_UPDATE) {
       target = av1_calc_iframe_target_size_one_pass_vbr(cpi);
     } else {
       target = av1_calc_pframe_target_size_one_pass_vbr(cpi, cur_update_type);
     }
   }
   gf_group->bit_allocation[cur_index] = target;
 }
}

static inline void set_baseline_gf_interval(PRIMARY_RATE_CONTROL *p_rc,
                                           int arf_position) {
 p_rc->baseline_gf_interval = arf_position;
}

// initialize GF_GROUP_STATS
static void init_gf_stats(GF_GROUP_STATS *gf_stats) {
 gf_stats->gf_group_err = 0.0;
 gf_stats->gf_group_raw_error = 0.0;
 gf_stats->gf_group_skip_pct = 0.0;
 gf_stats->gf_group_inactive_zone_rows = 0.0;

 gf_stats->mv_ratio_accumulator = 0.0;
 gf_stats->decay_accumulator = 1.0;
 gf_stats->zero_motion_accumulator = 1.0;
 gf_stats->loop_decay_rate = 1.0;
 gf_stats->last_loop_decay_rate = 1.0;
 gf_stats->this_frame_mv_in_out = 0.0;
 gf_stats->mv_in_out_accumulator = 0.0;
 gf_stats->abs_mv_in_out_accumulator = 0.0;

 gf_stats->avg_sr_coded_error = 0.0;
 gf_stats->avg_pcnt_second_ref = 0.0;
 gf_stats->avg_new_mv_count = 0.0;
 gf_stats->avg_wavelet_energy = 0.0;
 gf_stats->avg_raw_err_stdev = 0.0;
 gf_stats->non_zero_stdev_count = 0;
}

static void accumulate_gop_stats(AV1_COMP *cpi, int is_intra_only, int f_w,
                                int f_h, FIRSTPASS_STATS *next_frame,
                                const FIRSTPASS_STATS *start_pos,
                                GF_GROUP_STATS *gf_stats, int *idx) {
 int i, flash_detected;
 TWO_PASS *const twopass = &cpi->ppi->twopass;
 PRIMARY_RATE_CONTROL *const p_rc = &cpi->ppi->p_rc;
 RATE_CONTROL *const rc = &cpi->rc;
 FRAME_INFO *frame_info = &cpi->frame_info;
 const AV1EncoderConfig *const oxcf = &cpi->oxcf;

 init_gf_stats(gf_stats);
 av1_zero(*next_frame);

 // If this is a key frame or the overlay from a previous arf then
 // the error score / cost of this frame has already been accounted for.
 i = is_intra_only;
 // get the determined gf group length from p_rc->gf_intervals
 while (i < p_rc->gf_intervals[p_rc->cur_gf_index]) {
   // read in the next frame
   if (EOF == input_stats(twopass, &cpi->twopass_frame, next_frame)) break;
   // Accumulate error score of frames in this gf group.
   double mod_frame_err =
       calculate_modified_err(frame_info, twopass, oxcf, next_frame);
   // accumulate stats for this frame
   accumulate_this_frame_stats(next_frame, mod_frame_err, gf_stats);
   ++i;
 }

 reset_fpf_position(&cpi->twopass_frame, start_pos);

 i = is_intra_only;
 input_stats(twopass, &cpi->twopass_frame, next_frame);
 while (i < p_rc->gf_intervals[p_rc->cur_gf_index]) {
   // read in the next frame
   if (EOF == input_stats(twopass, &cpi->twopass_frame, next_frame)) break;

   // Test for the case where there is a brief flash but the prediction
   // quality back to an earlier frame is then restored.
   flash_detected = detect_flash(twopass, &cpi->twopass_frame, 0);

   // accumulate stats for next frame
   accumulate_next_frame_stats(next_frame, flash_detected,
                               rc->frames_since_key, i, gf_stats, f_w, f_h);

   ++i;
 }

 i = p_rc->gf_intervals[p_rc->cur_gf_index];
 average_gf_stats(i, gf_stats);

 *idx = i;
}

static void update_gop_length(RATE_CONTROL *rc, PRIMARY_RATE_CONTROL *p_rc,
                             int idx, int is_final_pass) {
 if (is_final_pass) {
   rc->intervals_till_gf_calculate_due--;
   p_rc->cur_gf_index++;
 }

 // Was the group length constrained by the requirement for a new KF?
 p_rc->constrained_gf_group = (idx >= rc->frames_to_key) ? 1 : 0;

 set_baseline_gf_interval(p_rc, idx);
 rc->frames_till_gf_update_due = p_rc->baseline_gf_interval;
}

// #define FIXED_ARF_BITS
#ifdef FIXED_ARF_BITS
#define ARF_BITS_FRACTION 0.75
#endif
/*!\brief Distributes bits to frames in a group
*
*\ingroup rate_control
*
* This function decides on the allocation of bits between the different
* frames and types of frame in a GF/ARF group.
*
* \param[in]   cpi           Top - level encoder instance structure
* \param[in]   rc            Rate control data
* \param[in]   gf_group      GF/ARF group data structure
* \param[in]   is_key_frame  Indicates if the first frame in the group is
*                            also a key frame.
* \param[in]   use_arf       Are ARF frames enabled or is this a GF only
*                            uni-directional group.
* \param[in]   gf_group_bits Bits available to be allocated.
*
* \remark No return but updates the rate control and group data structures
*         to reflect the allocation of bits.
*/
void av1_gop_bit_allocation(const AV1_COMP *cpi, RATE_CONTROL *const rc,
                           GF_GROUP *gf_group, int is_key_frame, int use_arf,
                           int64_t gf_group_bits) {
 PRIMARY_RATE_CONTROL *const p_rc = &cpi->ppi->p_rc;
 // Calculate the extra bits to be used for boosted frame(s)
#ifdef FIXED_ARF_BITS
 int gf_arf_bits = (int)(ARF_BITS_FRACTION * gf_group_bits);
#else
 int gf_arf_bits = calculate_boost_bits(
     p_rc->baseline_gf_interval - (rc->frames_since_key == 0), p_rc->gfu_boost,
     gf_group_bits);
#endif

 gf_arf_bits = adjust_boost_bits_for_target_level(cpi, rc, gf_arf_bits,
                                                  gf_group_bits, 1);

 // Allocate bits to each of the frames in the GF group.
 allocate_gf_group_bits(gf_group, p_rc, rc, gf_group_bits, gf_arf_bits,
                        is_key_frame, use_arf);
}
#undef ARF_BITS_FRACTION

#define MAX_GF_BOOST 5400
#define REDUCE_GF_LENGTH_THRESH 4
#define REDUCE_GF_LENGTH_TO_KEY_THRESH 9
#define REDUCE_GF_LENGTH_BY 1
static void set_gop_bits_boost(AV1_COMP *cpi, int i, int is_intra_only,
                              int is_final_pass, int use_alt_ref,
                              int alt_offset, const FIRSTPASS_STATS *start_pos,
                              GF_GROUP_STATS *gf_stats) {
 // Should we use the alternate reference frame.
 AV1_COMMON *const cm = &cpi->common;
 RATE_CONTROL *const rc = &cpi->rc;
 PRIMARY_RATE_CONTROL *const p_rc = &cpi->ppi->p_rc;
 TWO_PASS *const twopass = &cpi->ppi->twopass;
 GF_GROUP *gf_group = &cpi->ppi->gf_group;
 FRAME_INFO *frame_info = &cpi->frame_info;
 const AV1EncoderConfig *const oxcf = &cpi->oxcf;
 const RateControlCfg *const rc_cfg = &oxcf->rc_cfg;

 int ext_len = i - is_intra_only;
 if (use_alt_ref) {
   const int forward_frames = (rc->frames_to_key - i >= ext_len)
                                  ? ext_len
                                  : AOMMAX(0, rc->frames_to_key - i);

   // Calculate the boost for alt ref.
   p_rc->gfu_boost = av1_calc_arf_boost(
       twopass, &cpi->twopass_frame, p_rc, frame_info, alt_offset,
       forward_frames, ext_len, &p_rc->num_stats_used_for_gfu_boost,
       &p_rc->num_stats_required_for_gfu_boost, cpi->ppi->lap_enabled);
 } else {
   reset_fpf_position(&cpi->twopass_frame, start_pos);
   p_rc->gfu_boost = AOMMIN(
       MAX_GF_BOOST,
       av1_calc_arf_boost(
           twopass, &cpi->twopass_frame, p_rc, frame_info, alt_offset, ext_len,
           0, &p_rc->num_stats_used_for_gfu_boost,
           &p_rc->num_stats_required_for_gfu_boost, cpi->ppi->lap_enabled));
 }

#define LAST_ALR_BOOST_FACTOR 0.2f
 p_rc->arf_boost_factor = 1.0;
 if (use_alt_ref && !is_lossless_requested(rc_cfg)) {
   // Reduce the boost of altref in the last gf group
   if (rc->frames_to_key - ext_len == REDUCE_GF_LENGTH_BY ||
       rc->frames_to_key - ext_len == 0) {
     p_rc->arf_boost_factor = LAST_ALR_BOOST_FACTOR;
   }
 }

 // Reset the file position.
 reset_fpf_position(&cpi->twopass_frame, start_pos);
 if (cpi->ppi->lap_enabled) {
   // Since we don't have enough stats to know the actual error of the
   // gf group, we assume error of each frame to be equal to 1 and set
   // the error of the group as baseline_gf_interval.
   gf_stats->gf_group_err = p_rc->baseline_gf_interval;
 }
 // Calculate the bits to be allocated to the gf/arf group as a whole
 p_rc->gf_group_bits =
     calculate_total_gf_group_bits(cpi, gf_stats->gf_group_err);

#if GROUP_ADAPTIVE_MAXQ
 // Calculate an estimate of the maxq needed for the group.
 // We are more aggressive about correcting for sections
 // where there could be significant overshoot than for easier
 // sections where we do not wish to risk creating an overshoot
 // of the allocated bit budget.
 if ((rc_cfg->mode != AOM_Q) && (p_rc->baseline_gf_interval > 1) &&
     is_final_pass) {
   const int vbr_group_bits_per_frame =
       (int)(p_rc->gf_group_bits / p_rc->baseline_gf_interval);
   const double group_av_err =
       gf_stats->gf_group_raw_error / p_rc->baseline_gf_interval;
   const double group_av_skip_pct =
       gf_stats->gf_group_skip_pct / p_rc->baseline_gf_interval;
   const double group_av_inactive_zone =
       ((gf_stats->gf_group_inactive_zone_rows * 2) /
        (p_rc->baseline_gf_interval * (double)cm->mi_params.mb_rows));

   int tmp_q;
   tmp_q = get_twopass_worst_quality(
       cpi, group_av_err, (group_av_skip_pct + group_av_inactive_zone),
       vbr_group_bits_per_frame);
   rc->active_worst_quality = AOMMAX(tmp_q, rc->active_worst_quality >> 1);
 }
#endif

 // Adjust KF group bits and error remaining.
 if (is_final_pass) twopass->kf_group_error_left -= gf_stats->gf_group_err;

 // Reset the file position.
 reset_fpf_position(&cpi->twopass_frame, start_pos);

 // Calculate a section intra ratio used in setting max loop filter.
 if (rc->frames_since_key != 0) {
   twopass->section_intra_rating = calculate_section_intra_ratio(
       start_pos, twopass->stats_buf_ctx->stats_in_end,
       p_rc->baseline_gf_interval);
 }

 av1_gop_bit_allocation(cpi, rc, gf_group, rc->frames_since_key == 0,
                        use_alt_ref, p_rc->gf_group_bits);

 // TODO(jingning): Generalize this condition.
 if (is_final_pass) {
   cpi->ppi->gf_state.arf_gf_boost_lst = use_alt_ref;

   // Reset rolling actual and target bits counters for ARF groups.
   twopass->rolling_arf_group_target_bits = 1;
   twopass->rolling_arf_group_actual_bits = 1;
 }
#if CONFIG_BITRATE_ACCURACY
 if (is_final_pass) {
   av1_vbr_rc_set_gop_bit_budget(&cpi->vbr_rc_info,
                                 p_rc->baseline_gf_interval);
 }
#endif
}

/*!\brief Define a GF group.
*
* \ingroup gf_group_algo
* This function defines the structure of a GF group, along with various
* parameters regarding bit-allocation and quality setup.
*
* \param[in]    cpi             Top-level encoder structure
* \param[in]    frame_params    Structure with frame parameters
* \param[in]    is_final_pass   Whether this is the final pass for the
*                               GF group, or a trial (non-zero)
*
* \remark Nothing is returned. Instead, cpi->ppi->gf_group is changed.
*/
static void define_gf_group(AV1_COMP *cpi, EncodeFrameParams *frame_params,
                           int is_final_pass) {
 AV1_COMMON *const cm = &cpi->common;
 RATE_CONTROL *const rc = &cpi->rc;
 PRIMARY_RATE_CONTROL *const p_rc = &cpi->ppi->p_rc;
 const AV1EncoderConfig *const oxcf = &cpi->oxcf;
 TWO_PASS *const twopass = &cpi->ppi->twopass;
 FIRSTPASS_STATS next_frame;
 const FIRSTPASS_STATS *const start_pos = cpi->twopass_frame.stats_in;
 GF_GROUP *gf_group = &cpi->ppi->gf_group;
 const GFConfig *const gf_cfg = &oxcf->gf_cfg;
 const RateControlCfg *const rc_cfg = &oxcf->rc_cfg;
 const int f_w = cm->width;
 const int f_h = cm->height;
 int i;
 const int is_intra_only = rc->frames_since_key == 0;

 cpi->ppi->internal_altref_allowed = (gf_cfg->gf_max_pyr_height > 1);

 // Reset the GF group data structures unless this is a key
 // frame in which case it will already have been done.
 if (!is_intra_only) {
   av1_zero(cpi->ppi->gf_group);
   cpi->gf_frame_index = 0;
 }

 if (has_no_stats_stage(cpi)) {
   define_gf_group_pass0(cpi);
   return;
 }

#if CONFIG_THREE_PASS
 if (cpi->third_pass_ctx && oxcf->pass == AOM_RC_THIRD_PASS) {
   int ret = define_gf_group_pass3(cpi, frame_params, is_final_pass);
   if (ret == 0) return;

   av1_free_thirdpass_ctx(cpi->third_pass_ctx);
   cpi->third_pass_ctx = NULL;
 }
#endif  // CONFIG_THREE_PASS

 // correct frames_to_key when lookahead queue is emptying
 if (cpi->ppi->lap_enabled) {
   correct_frames_to_key(cpi);
 }

 GF_GROUP_STATS gf_stats;
 accumulate_gop_stats(cpi, is_intra_only, f_w, f_h, &next_frame, start_pos,
                      &gf_stats, &i);

 const int can_disable_arf = !gf_cfg->gf_min_pyr_height;

 // If this is a key frame or the overlay from a previous arf then
 // the error score / cost of this frame has already been accounted for.
 const int active_min_gf_interval = rc->min_gf_interval;

 // Disable internal ARFs for "still" gf groups.
 //   zero_motion_accumulator: minimum percentage of (0,0) motion;
 //   avg_sr_coded_error:      average of the SSE per pixel of each frame;
 //   avg_raw_err_stdev:       average of the standard deviation of (0,0)
 //                            motion error per block of each frame.
 const int can_disable_internal_arfs = gf_cfg->gf_min_pyr_height <= 1;
 if (can_disable_internal_arfs &&
     gf_stats.zero_motion_accumulator > MIN_ZERO_MOTION &&
     gf_stats.avg_sr_coded_error < MAX_SR_CODED_ERROR &&
     gf_stats.avg_raw_err_stdev < MAX_RAW_ERR_VAR) {
   cpi->ppi->internal_altref_allowed = 0;
 }

 int use_alt_ref;
 if (can_disable_arf) {
   use_alt_ref =
       !is_almost_static(gf_stats.zero_motion_accumulator,
                         twopass->kf_zeromotion_pct, cpi->ppi->lap_enabled) &&
       p_rc->use_arf_in_this_kf_group && (i < gf_cfg->lag_in_frames) &&
       (i >= MIN_GF_INTERVAL);
 } else {
   use_alt_ref = p_rc->use_arf_in_this_kf_group &&
                 (i < gf_cfg->lag_in_frames) && (i > 2);
 }
 if (use_alt_ref) {
   gf_group->max_layer_depth_allowed = gf_cfg->gf_max_pyr_height;
 } else {
   gf_group->max_layer_depth_allowed = 0;
 }

 int alt_offset = 0;
 // The length reduction strategy is tweaked for certain cases, and doesn't
 // work well for certain other cases.
 const int allow_gf_length_reduction =
     ((rc_cfg->mode == AOM_Q && rc_cfg->cq_level <= 128) ||
      !cpi->ppi->internal_altref_allowed) &&
     !is_lossless_requested(rc_cfg);

 if (allow_gf_length_reduction && use_alt_ref) {
   // adjust length of this gf group if one of the following condition met
   // 1: only one overlay frame left and this gf is too long
   // 2: next gf group is too short to have arf compared to the current gf

   // maximum length of next gf group
   const int next_gf_len = rc->frames_to_key - i;
   const int single_overlay_left =
       next_gf_len == 0 && i > REDUCE_GF_LENGTH_THRESH;
   // the next gf is probably going to have a ARF but it will be shorter than
   // this gf
   const int unbalanced_gf =
       i > REDUCE_GF_LENGTH_TO_KEY_THRESH &&
       next_gf_len + 1 < REDUCE_GF_LENGTH_TO_KEY_THRESH &&
       next_gf_len + 1 >= rc->min_gf_interval;

   if (single_overlay_left || unbalanced_gf) {
     const int roll_back = REDUCE_GF_LENGTH_BY;
     // Reduce length only if active_min_gf_interval will be respected later.
     if (i - roll_back >= active_min_gf_interval + 1) {
       alt_offset = -roll_back;
       i -= roll_back;
       if (is_final_pass) rc->intervals_till_gf_calculate_due = 0;
       p_rc->gf_intervals[p_rc->cur_gf_index] -= roll_back;
       reset_fpf_position(&cpi->twopass_frame, start_pos);
       accumulate_gop_stats(cpi, is_intra_only, f_w, f_h, &next_frame,
                            start_pos, &gf_stats, &i);
     }
   }
 }

 update_gop_length(rc, p_rc, i, is_final_pass);

 // Set up the structure of this Group-Of-Pictures (same as GF_GROUP)
 av1_gop_setup_structure(cpi);

 set_gop_bits_boost(cpi, i, is_intra_only, is_final_pass, use_alt_ref,
                    alt_offset, start_pos, &gf_stats);

 frame_params->frame_type =
     rc->frames_since_key == 0 ? KEY_FRAME : INTER_FRAME;
 frame_params->show_frame =
     !(gf_group->update_type[cpi->gf_frame_index] == ARF_UPDATE ||
       gf_group->update_type[cpi->gf_frame_index] == INTNL_ARF_UPDATE);
}

#if CONFIG_THREE_PASS
/*!\brief Define a GF group for the third apss.
*
* \ingroup gf_group_algo
* This function defines the structure of a GF group for the third pass, along
* with various parameters regarding bit-allocation and quality setup based on
* the two-pass bitstream.
* Much of the function still uses the strategies used for the second pass and
* relies on first pass statistics. It is expected that over time these portions
* would be replaced with strategies specific to the third pass.
*
* \param[in]    cpi             Top-level encoder structure
* \param[in]    frame_params    Structure with frame parameters
* \param[in]    is_final_pass   Whether this is the final pass for the
*                               GF group, or a trial (non-zero)
*
* \return       0: Success;
*              -1: There are conflicts between the bitstream and current config
*               The values in cpi->ppi->gf_group are also changed.
*/
static int define_gf_group_pass3(AV1_COMP *cpi, EncodeFrameParams *frame_params,
                                int is_final_pass) {
 if (!cpi->third_pass_ctx) return -1;
 AV1_COMMON *const cm = &cpi->common;
 RATE_CONTROL *const rc = &cpi->rc;
 PRIMARY_RATE_CONTROL *const p_rc = &cpi->ppi->p_rc;
 const AV1EncoderConfig *const oxcf = &cpi->oxcf;
 FIRSTPASS_STATS next_frame;
 const FIRSTPASS_STATS *const start_pos = cpi->twopass_frame.stats_in;
 GF_GROUP *gf_group = &cpi->ppi->gf_group;
 const GFConfig *const gf_cfg = &oxcf->gf_cfg;
 const int f_w = cm->width;
 const int f_h = cm->height;
 int i;
 const int is_intra_only = rc->frames_since_key == 0;

 cpi->ppi->internal_altref_allowed = (gf_cfg->gf_max_pyr_height > 1);

 // Reset the GF group data structures unless this is a key
 // frame in which case it will already have been done.
 if (!is_intra_only) {
   av1_zero(cpi->ppi->gf_group);
   cpi->gf_frame_index = 0;
 }

 GF_GROUP_STATS gf_stats;
 accumulate_gop_stats(cpi, is_intra_only, f_w, f_h, &next_frame, start_pos,
                      &gf_stats, &i);

 const int can_disable_arf = !gf_cfg->gf_min_pyr_height;

 // TODO(any): set cpi->ppi->internal_altref_allowed accordingly;

 int use_alt_ref = av1_check_use_arf(cpi->third_pass_ctx);
 if (use_alt_ref == 0 && !can_disable_arf) return -1;
 if (use_alt_ref) {
   gf_group->max_layer_depth_allowed = gf_cfg->gf_max_pyr_height;
 } else {
   gf_group->max_layer_depth_allowed = 0;
 }

 update_gop_length(rc, p_rc, i, is_final_pass);

 // Set up the structure of this Group-Of-Pictures (same as GF_GROUP)
 av1_gop_setup_structure(cpi);

 set_gop_bits_boost(cpi, i, is_intra_only, is_final_pass, use_alt_ref, 0,
                    start_pos, &gf_stats);

 frame_params->frame_type = cpi->third_pass_ctx->frame_info[0].frame_type;
 frame_params->show_frame = cpi->third_pass_ctx->frame_info[0].is_show_frame;
 return 0;
}
#endif  // CONFIG_THREE_PASS

// Minimum % intra coding observed in first pass (1.0 = 100%)
#define MIN_INTRA_LEVEL 0.25
// Minimum ratio between the % of intra coding and inter coding in the first
// pass after discounting neutral blocks (discounting neutral blocks in this
// way helps catch scene cuts in clips with very flat areas or letter box
// format clips with image padding.
#define INTRA_VS_INTER_THRESH 2.0
// Hard threshold where the first pass chooses intra for almost all blocks.
// In such a case even if the frame is not a scene cut coding a key frame
// may be a good option.
#define VERY_LOW_INTER_THRESH 0.05
// Maximum threshold for the relative ratio of intra error score vs best
// inter error score.
#define KF_II_ERR_THRESHOLD 1.9
// In real scene cuts there is almost always a sharp change in the intra
// or inter error score.
#define ERR_CHANGE_THRESHOLD 0.4
// For real scene cuts we expect an improvment in the intra inter error
// ratio in the next frame.
#define II_IMPROVEMENT_THRESHOLD 3.5
#define KF_II_MAX 128.0
// Intra / Inter threshold very low
#define VERY_LOW_II 1.5
// Clean slide transitions we expect a sharp single frame spike in error.
#define ERROR_SPIKE 5.0

// Slide show transition detection.
// Tests for case where there is very low error either side of the current frame
// but much higher just for this frame. This can help detect key frames in
// slide shows even where the slides are pictures of different sizes.
// Also requires that intra and inter errors are very similar to help eliminate
// harmful false positives.
// It will not help if the transition is a fade or other multi-frame effect.
static int slide_transition(const FIRSTPASS_STATS *this_frame,
                           const FIRSTPASS_STATS *last_frame,
                           const FIRSTPASS_STATS *next_frame) {
 return (this_frame->intra_error < (this_frame->coded_error * VERY_LOW_II)) &&
        (this_frame->coded_error > (last_frame->coded_error * ERROR_SPIKE)) &&
        (this_frame->coded_error > (next_frame->coded_error * ERROR_SPIKE));
}

// Threshold for use of the lagging second reference frame. High second ref
// usage may point to a transient event like a flash or occlusion rather than
// a real scene cut.
// We adapt the threshold based on number of frames in this key-frame group so
// far.
static double get_second_ref_usage_thresh(int frame_count_so_far) {
 const int adapt_upto = 32;
 const double min_second_ref_usage_thresh = 0.085;
 const double second_ref_usage_thresh_max_delta = 0.035;
 if (frame_count_so_far >= adapt_upto) {
   return min_second_ref_usage_thresh + second_ref_usage_thresh_max_delta;
 }
 return min_second_ref_usage_thresh +
        ((double)frame_count_so_far / (adapt_upto - 1)) *
            second_ref_usage_thresh_max_delta;
}

static int test_candidate_kf(const FIRSTPASS_INFO *firstpass_info,
                            int this_stats_index, int frame_count_so_far,
                            enum aom_rc_mode rc_mode, int scenecut_mode,
                            int num_mbs) {
 const FIRSTPASS_STATS *last_stats =
     av1_firstpass_info_peek(firstpass_info, this_stats_index - 1);
 const FIRSTPASS_STATS *this_stats =
     av1_firstpass_info_peek(firstpass_info, this_stats_index);
 const FIRSTPASS_STATS *next_stats =
     av1_firstpass_info_peek(firstpass_info, this_stats_index + 1);
 if (last_stats == NULL || this_stats == NULL || next_stats == NULL) {
   return 0;
 }

 int is_viable_kf = 0;
 double pcnt_intra = 1.0 - this_stats->pcnt_inter;
 double modified_pcnt_inter =
     this_stats->pcnt_inter - this_stats->pcnt_neutral;
 const double second_ref_usage_thresh =
     get_second_ref_usage_thresh(frame_count_so_far);
 int frames_to_test_after_candidate_key = SCENE_CUT_KEY_TEST_INTERVAL;
 int count_for_tolerable_prediction = 3;

 // We do "-1" because the candidate key is not counted.
 int stats_after_this_stats =
     av1_firstpass_info_future_count(firstpass_info, this_stats_index) - 1;

 if (scenecut_mode == ENABLE_SCENECUT_MODE_1) {
   if (stats_after_this_stats < 3) {
     return 0;
   } else {
     frames_to_test_after_candidate_key = 3;
     count_for_tolerable_prediction = 1;
   }
 }
 // Make sure we have enough stats after the candidate key.
 frames_to_test_after_candidate_key =
     AOMMIN(frames_to_test_after_candidate_key, stats_after_this_stats);

 // Does the frame satisfy the primary criteria of a key frame?
 // See above for an explanation of the test criteria.
 // If so, then examine how well it predicts subsequent frames.
 if (IMPLIES(rc_mode == AOM_Q, frame_count_so_far >= 3) &&
     (this_stats->pcnt_second_ref < second_ref_usage_thresh) &&
     (next_stats->pcnt_second_ref < second_ref_usage_thresh) &&
     ((this_stats->pcnt_inter < VERY_LOW_INTER_THRESH) ||
      slide_transition(this_stats, last_stats, next_stats) ||
      ((pcnt_intra > MIN_INTRA_LEVEL) &&
       (pcnt_intra > (INTRA_VS_INTER_THRESH * modified_pcnt_inter)) &&
       ((this_stats->intra_error /
         DOUBLE_DIVIDE_CHECK(this_stats->coded_error)) <
        KF_II_ERR_THRESHOLD) &&
       ((fabs(last_stats->coded_error - this_stats->coded_error) /
             DOUBLE_DIVIDE_CHECK(this_stats->coded_error) >
         ERR_CHANGE_THRESHOLD) ||
        (fabs(last_stats->intra_error - this_stats->intra_error) /
             DOUBLE_DIVIDE_CHECK(this_stats->intra_error) >
         ERR_CHANGE_THRESHOLD) ||
        ((next_stats->intra_error /
          DOUBLE_DIVIDE_CHECK(next_stats->coded_error)) >
         II_IMPROVEMENT_THRESHOLD))))) {
   int i;
   double boost_score = 0.0;
   double old_boost_score = 0.0;
   double decay_accumulator = 1.0;

   // Examine how well the key frame predicts subsequent frames.
   for (i = 1; i <= frames_to_test_after_candidate_key; ++i) {
     // Get the next frame details
     const FIRSTPASS_STATS *local_next_frame =
         av1_firstpass_info_peek(firstpass_info, this_stats_index + i);
     double next_iiratio =
         (BOOST_FACTOR * local_next_frame->intra_error /
          DOUBLE_DIVIDE_CHECK(local_next_frame->coded_error));

     if (next_iiratio > KF_II_MAX) next_iiratio = KF_II_MAX;

     // Cumulative effect of decay in prediction quality.
     if (local_next_frame->pcnt_inter > 0.85)
       decay_accumulator *= local_next_frame->pcnt_inter;
     else
       decay_accumulator *= (0.85 + local_next_frame->pcnt_inter) / 2.0;

     // Keep a running total.
     boost_score += (decay_accumulator * next_iiratio);

     // Test various breakout clauses.
     // TODO(any): Test of intra error should be normalized to an MB.
     if ((local_next_frame->pcnt_inter < 0.05) || (next_iiratio < 1.5) ||
         (((local_next_frame->pcnt_inter - local_next_frame->pcnt_neutral) <
           0.20) &&
          (next_iiratio < 3.0)) ||
         ((boost_score - old_boost_score) < 3.0) ||
         (local_next_frame->intra_error < (200.0 / (double)num_mbs))) {
       break;
     }

     old_boost_score = boost_score;
   }

   // If there is tolerable prediction for at least the next 3 frames then
   // break out else discard this potential key frame and move on
   if (boost_score > 30.0 && (i > count_for_tolerable_prediction)) {
     is_viable_kf = 1;
   } else {
     is_viable_kf = 0;
   }
 }
 return is_viable_kf;
}

#define FRAMES_TO_CHECK_DECAY 8
#define KF_MIN_FRAME_BOOST 80.0
#define KF_MAX_FRAME_BOOST 128.0
#define MIN_KF_BOOST 600  // Minimum boost for non-static KF interval
#define MAX_KF_BOOST 3200
#define MIN_STATIC_KF_BOOST 5400  // Minimum boost for static KF interval

static int detect_app_forced_key(AV1_COMP *cpi) {
 int num_frames_to_app_forced_key = is_forced_keyframe_pending(
     cpi->ppi->lookahead, cpi->ppi->lookahead->max_sz, cpi->compressor_stage);
 return num_frames_to_app_forced_key;
}

static int get_projected_kf_boost(AV1_COMP *cpi) {
 /*
  * If num_stats_used_for_kf_boost >= frames_to_key, then
  * all stats needed for prior boost calculation are available.
  * Hence projecting the prior boost is not needed in this cases.
  */
 if (cpi->ppi->p_rc.num_stats_used_for_kf_boost >= cpi->rc.frames_to_key)
   return cpi->ppi->p_rc.kf_boost;

 // Get the current tpl factor (number of frames = frames_to_key).
 double tpl_factor = av1_get_kf_boost_projection_factor(cpi->rc.frames_to_key);
 // Get the tpl factor when number of frames = num_stats_used_for_kf_boost.
 double tpl_factor_num_stats = av1_get_kf_boost_projection_factor(
     cpi->ppi->p_rc.num_stats_used_for_kf_boost);
 int projected_kf_boost =
     (int)rint((tpl_factor * cpi->ppi->p_rc.kf_boost) / tpl_factor_num_stats);
 return projected_kf_boost;
}

/*!\brief Determine the location of the next key frame
*
* \ingroup gf_group_algo
* This function decides the placement of the next key frame when a
* scenecut is detected or the maximum key frame distance is reached.
*
* \param[in]    cpi              Top-level encoder structure
* \param[in]    firstpass_info   struct for firstpass info
* \param[in]    num_frames_to_detect_scenecut Maximum lookahead frames.
* \param[in]    search_start_idx   the start index for searching key frame.
*                                  Set it to one if we already know the
*                                  current frame is key frame. Otherwise,
*                                  set it to zero.
*
* \return       Number of frames to the next key including the current frame.
*/
static int define_kf_interval(AV1_COMP *cpi,
                             const FIRSTPASS_INFO *firstpass_info,
                             int num_frames_to_detect_scenecut,
                             int search_start_idx) {
 const TWO_PASS *const twopass = &cpi->ppi->twopass;
 const RATE_CONTROL *const rc = &cpi->rc;
 PRIMARY_RATE_CONTROL *const p_rc = &cpi->ppi->p_rc;
 const AV1EncoderConfig *const oxcf = &cpi->oxcf;
 const KeyFrameCfg *const kf_cfg = &oxcf->kf_cfg;
 double recent_loop_decay[FRAMES_TO_CHECK_DECAY];
 double decay_accumulator = 1.0;
 int i = 0, j;
 int frames_to_key = search_start_idx;
 int frames_since_key = rc->frames_since_key + 1;
 int scenecut_detected = 0;

 int num_frames_to_next_key = detect_app_forced_key(cpi);

 if (num_frames_to_detect_scenecut == 0) {
   if (num_frames_to_next_key != -1)
     return num_frames_to_next_key;
   else
     return rc->frames_to_key;
 }

 if (num_frames_to_next_key != -1)
   num_frames_to_detect_scenecut =
       AOMMIN(num_frames_to_detect_scenecut, num_frames_to_next_key);

 // Initialize the decay rates for the recent frames to check
 for (j = 0; j < FRAMES_TO_CHECK_DECAY; ++j) recent_loop_decay[j] = 1.0;

 i = 0;
 const int num_mbs = (oxcf->resize_cfg.resize_mode != RESIZE_NONE)
                         ? cpi->initial_mbs
                         : cpi->common.mi_params.MBs;
 const int future_stats_count =
     av1_firstpass_info_future_count(firstpass_info, 0);
 while (frames_to_key < future_stats_count &&
        frames_to_key < num_frames_to_detect_scenecut) {
   // Provided that we are not at the end of the file...
   if ((cpi->ppi->p_rc.enable_scenecut_detection > 0) && kf_cfg->auto_key &&
       frames_to_key + 1 < future_stats_count) {
     double loop_decay_rate;

     // Check for a scene cut.
     if (frames_since_key >= kf_cfg->key_freq_min) {
       scenecut_detected = test_candidate_kf(
           &twopass->firstpass_info, frames_to_key, frames_since_key,
           oxcf->rc_cfg.mode, cpi->ppi->p_rc.enable_scenecut_detection,
           num_mbs);
       if (scenecut_detected) {
         break;
       }
     }

     // How fast is the prediction quality decaying?
     const FIRSTPASS_STATS *next_stats =
         av1_firstpass_info_peek(firstpass_info, frames_to_key + 1);
     loop_decay_rate = get_prediction_decay_rate(next_stats);

     // We want to know something about the recent past... rather than
     // as used elsewhere where we are concerned with decay in prediction
     // quality since the last GF or KF.
     recent_loop_decay[i % FRAMES_TO_CHECK_DECAY] = loop_decay_rate;
     decay_accumulator = 1.0;
     for (j = 0; j < FRAMES_TO_CHECK_DECAY; ++j)
       decay_accumulator *= recent_loop_decay[j];

     // Special check for transition or high motion followed by a
     // static scene.
     if (frames_since_key >= kf_cfg->key_freq_min) {
       scenecut_detected = detect_transition_to_still(
           firstpass_info, frames_to_key + 1, rc->min_gf_interval, i,
           kf_cfg->key_freq_max - i, loop_decay_rate, decay_accumulator);
       if (scenecut_detected) {
         // In the case of transition followed by a static scene, the key frame
         // could be a good predictor for the following frames, therefore we
         // do not use an arf.
         p_rc->use_arf_in_this_kf_group = 0;
         break;
       }
     }

     // Step on to the next frame.
     ++frames_to_key;
     ++frames_since_key;

     // If we don't have a real key frame within the next two
     // key_freq_max intervals then break out of the loop.
     if (frames_to_key >= 2 * kf_cfg->key_freq_max) {
       break;
     }
   } else {
     ++frames_to_key;
     ++frames_since_key;
   }
   ++i;
 }
 if (cpi->ppi->lap_enabled && !scenecut_detected)
   frames_to_key = num_frames_to_next_key;

 return frames_to_key;
}

static double get_kf_group_avg_error(TWO_PASS *twopass,
                                    TWO_PASS_FRAME *twopass_frame,
                                    const FIRSTPASS_STATS *first_frame,
                                    const FIRSTPASS_STATS *start_position,
                                    int frames_to_key) {
 FIRSTPASS_STATS cur_frame = *first_frame;
 int num_frames, i;
 double kf_group_avg_error = 0.0;

 reset_fpf_position(twopass_frame, start_position);

 for (i = 0; i < frames_to_key; ++i) {
   kf_group_avg_error += cur_frame.coded_error;
   if (EOF == input_stats(twopass, twopass_frame, &cur_frame)) break;
 }
 num_frames = i + 1;
 num_frames = AOMMIN(num_frames, frames_to_key);
 kf_group_avg_error = kf_group_avg_error / num_frames;

 return (kf_group_avg_error);
}

static int64_t get_kf_group_bits(AV1_COMP *cpi, double kf_group_err,
                                double kf_group_avg_error) {
 RATE_CONTROL *const rc = &cpi->rc;
 TWO_PASS *const twopass = &cpi->ppi->twopass;
 int64_t kf_group_bits;
 if (cpi->ppi->lap_enabled) {
   kf_group_bits = (int64_t)rc->frames_to_key * rc->avg_frame_bandwidth;
   if (cpi->oxcf.rc_cfg.vbr_corpus_complexity_lap) {
     double vbr_corpus_complexity_lap =
         cpi->oxcf.rc_cfg.vbr_corpus_complexity_lap / 10.0;
     /* Get the average corpus complexity of the frame */
     kf_group_bits = (int64_t)(kf_group_bits * (kf_group_avg_error /
                                                vbr_corpus_complexity_lap));
   }
 } else {
   kf_group_bits = (int64_t)(twopass->bits_left *
                             (kf_group_err / twopass->modified_error_left));
 }

 return kf_group_bits;
}

static int calc_avg_stats(AV1_COMP *cpi, FIRSTPASS_STATS *avg_frame_stat) {
 RATE_CONTROL *const rc = &cpi->rc;
 TWO_PASS *const twopass = &cpi->ppi->twopass;
 FIRSTPASS_STATS cur_frame;
 av1_zero(cur_frame);
 int num_frames = 0;
 // Accumulate total stat using available number of stats.
 for (num_frames = 0; num_frames < (rc->frames_to_key - 1); ++num_frames) {
   if (EOF == input_stats(twopass, &cpi->twopass_frame, &cur_frame)) break;
   av1_accumulate_stats(avg_frame_stat, &cur_frame);
 }

 if (num_frames < 2) {
   return num_frames;
 }
 // Average the total stat
 avg_frame_stat->weight = avg_frame_stat->weight / num_frames;
 avg_frame_stat->intra_error = avg_frame_stat->intra_error / num_frames;
 avg_frame_stat->frame_avg_wavelet_energy =
     avg_frame_stat->frame_avg_wavelet_energy / num_frames;
 avg_frame_stat->coded_error = avg_frame_stat->coded_error / num_frames;
 avg_frame_stat->sr_coded_error = avg_frame_stat->sr_coded_error / num_frames;
 avg_frame_stat->pcnt_inter = avg_frame_stat->pcnt_inter / num_frames;
 avg_frame_stat->pcnt_motion = avg_frame_stat->pcnt_motion / num_frames;
 avg_frame_stat->pcnt_second_ref =
     avg_frame_stat->pcnt_second_ref / num_frames;
 avg_frame_stat->pcnt_neutral = avg_frame_stat->pcnt_neutral / num_frames;
 avg_frame_stat->intra_skip_pct = avg_frame_stat->intra_skip_pct / num_frames;
 avg_frame_stat->inactive_zone_rows =
     avg_frame_stat->inactive_zone_rows / num_frames;
 avg_frame_stat->inactive_zone_cols =
     avg_frame_stat->inactive_zone_cols / num_frames;
 avg_frame_stat->MVr = avg_frame_stat->MVr / num_frames;
 avg_frame_stat->mvr_abs = avg_frame_stat->mvr_abs / num_frames;
 avg_frame_stat->MVc = avg_frame_stat->MVc / num_frames;
 avg_frame_stat->mvc_abs = avg_frame_stat->mvc_abs / num_frames;
 avg_frame_stat->MVrv = avg_frame_stat->MVrv / num_frames;
 avg_frame_stat->MVcv = avg_frame_stat->MVcv / num_frames;
 avg_frame_stat->mv_in_out_count =
     avg_frame_stat->mv_in_out_count / num_frames;
 avg_frame_stat->new_mv_count = avg_frame_stat->new_mv_count / num_frames;
 avg_frame_stat->count = avg_frame_stat->count / num_frames;
 avg_frame_stat->duration = avg_frame_stat->duration / num_frames;

 return num_frames;
}

static double get_kf_boost_score(AV1_COMP *cpi, double kf_raw_err,
                                double *zero_motion_accumulator,
                                double *sr_accumulator, int use_avg_stat) {
 RATE_CONTROL *const rc = &cpi->rc;
 TWO_PASS *const twopass = &cpi->ppi->twopass;
 FRAME_INFO *const frame_info = &cpi->frame_info;
 FIRSTPASS_STATS frame_stat;
 av1_zero(frame_stat);
 int i = 0, num_stat_used = 0;
 double boost_score = 0.0;
 const double kf_max_boost =
     cpi->oxcf.rc_cfg.mode == AOM_Q
         ? fclamp(rc->frames_to_key * 2.0, KF_MIN_FRAME_BOOST,
                  KF_MAX_FRAME_BOOST)
         : KF_MAX_FRAME_BOOST;

 // Calculate the average using available number of stats.
 if (use_avg_stat) num_stat_used = calc_avg_stats(cpi, &frame_stat);

 for (i = num_stat_used; i < (rc->frames_to_key - 1); ++i) {
   if (!use_avg_stat &&
       EOF == input_stats(twopass, &cpi->twopass_frame, &frame_stat))
     break;

   // Monitor for static sections.
   // For the first frame in kf group, the second ref indicator is invalid.
   if (i > 0) {
     *zero_motion_accumulator =
         AOMMIN(*zero_motion_accumulator, get_zero_motion_factor(&frame_stat));
   } else {
     *zero_motion_accumulator = frame_stat.pcnt_inter - frame_stat.pcnt_motion;
   }

   // Not all frames in the group are necessarily used in calculating boost.
   if ((*sr_accumulator < (kf_raw_err * 1.50)) &&
       (i <= rc->max_gf_interval * 2)) {
     double frame_boost;
     double zm_factor;

     // Factor 0.75-1.25 based on how much of frame is static.
     zm_factor = (0.75 + (*zero_motion_accumulator / 2.0));

     if (i < 2) *sr_accumulator = 0.0;
     frame_boost =
         calc_kf_frame_boost(&cpi->ppi->p_rc, frame_info, &frame_stat,
                             sr_accumulator, kf_max_boost);
     boost_score += frame_boost * zm_factor;
   }
 }
 return boost_score;
}

/*!\brief Interval(in seconds) to clip key-frame distance to in LAP.
*/
#define MAX_KF_BITS_INTERVAL_SINGLE_PASS 5

/*!\brief Determine the next key frame group
*
* \ingroup gf_group_algo
* This function decides the placement of the next key frame, and
* calculates the bit allocation of the KF group and the keyframe itself.
*
* \param[in]    cpi              Top-level encoder structure
* \param[in]    this_frame       Pointer to first pass stats
*/
static void find_next_key_frame(AV1_COMP *cpi, FIRSTPASS_STATS *this_frame) {
 RATE_CONTROL *const rc = &cpi->rc;
 PRIMARY_RATE_CONTROL *const p_rc = &cpi->ppi->p_rc;
 TWO_PASS *const twopass = &cpi->ppi->twopass;
 GF_GROUP *const gf_group = &cpi->ppi->gf_group;
 FRAME_INFO *const frame_info = &cpi->frame_info;
 AV1_COMMON *const cm = &cpi->common;
 CurrentFrame *const current_frame = &cm->current_frame;
 const AV1EncoderConfig *const oxcf = &cpi->oxcf;
 const KeyFrameCfg *const kf_cfg = &oxcf->kf_cfg;
 const FIRSTPASS_STATS first_frame = *this_frame;
 FIRSTPASS_STATS next_frame;
 const FIRSTPASS_INFO *firstpass_info = &twopass->firstpass_info;
 av1_zero(next_frame);

 rc->frames_since_key = 0;
 // Use arfs if possible.
 p_rc->use_arf_in_this_kf_group = is_altref_enabled(
     oxcf->gf_cfg.lag_in_frames, oxcf->gf_cfg.enable_auto_arf);

 // Reset the GF group data structures.
 av1_zero(*gf_group);
 cpi->gf_frame_index = 0;

 // KF is always a GF so clear frames till next gf counter.
 rc->frames_till_gf_update_due = 0;

 if (has_no_stats_stage(cpi)) {
   int num_frames_to_app_forced_key = detect_app_forced_key(cpi);
   p_rc->this_key_frame_forced =
       current_frame->frame_number != 0 && rc->frames_to_key == 0;
   if (num_frames_to_app_forced_key != -1)
     rc->frames_to_key = num_frames_to_app_forced_key;
   else
     rc->frames_to_key = AOMMAX(1, kf_cfg->key_freq_max);
   correct_frames_to_key(cpi);
   p_rc->kf_boost = DEFAULT_KF_BOOST;
   gf_group->update_type[0] = KF_UPDATE;
   return;
 }
 int i;
 const FIRSTPASS_STATS *const start_position = cpi->twopass_frame.stats_in;
 int kf_bits = 0;
 double zero_motion_accumulator = 1.0;
 double boost_score = 0.0;
 double kf_raw_err = 0.0;
 double kf_mod_err = 0.0;
 double sr_accumulator = 0.0;
 double kf_group_avg_error = 0.0;
 int frames_to_key, frames_to_key_clipped = INT_MAX;
 int64_t kf_group_bits_clipped = INT64_MAX;

 // Is this a forced key frame by interval.
 p_rc->this_key_frame_forced = p_rc->next_key_frame_forced;

 twopass->kf_group_bits = 0;        // Total bits available to kf group
 twopass->kf_group_error_left = 0;  // Group modified error score.

 kf_raw_err = this_frame->intra_error;
 kf_mod_err = calculate_modified_err(frame_info, twopass, oxcf, this_frame);

 // We assume the current frame is a key frame and we are looking for the next
 // key frame. Therefore search_start_idx = 1
 frames_to_key = define_kf_interval(cpi, firstpass_info, kf_cfg->key_freq_max,
                                    /*search_start_idx=*/1);

 if (frames_to_key != -1) {
   rc->frames_to_key = AOMMIN(kf_cfg->key_freq_max, frames_to_key);
 } else {
   rc->frames_to_key = kf_cfg->key_freq_max;
 }

 if (cpi->ppi->lap_enabled) correct_frames_to_key(cpi);

 // If there is a max kf interval set by the user we must obey it.
 // We already breakout of the loop above at 2x max.
 // This code centers the extra kf if the actual natural interval
 // is between 1x and 2x.
 if (kf_cfg->auto_key && rc->frames_to_key > kf_cfg->key_freq_max) {
   FIRSTPASS_STATS tmp_frame = first_frame;

   rc->frames_to_key /= 2;

   // Reset to the start of the group.
   reset_fpf_position(&cpi->twopass_frame, start_position);
   // Rescan to get the correct error data for the forced kf group.
   for (i = 0; i < rc->frames_to_key; ++i) {
     if (EOF == input_stats(twopass, &cpi->twopass_frame, &tmp_frame)) break;
   }
   p_rc->next_key_frame_forced = 1;
 } else if ((cpi->twopass_frame.stats_in ==
                 twopass->stats_buf_ctx->stats_in_end &&
             is_stat_consumption_stage_twopass(cpi)) ||
            rc->frames_to_key >= kf_cfg->key_freq_max) {
   p_rc->next_key_frame_forced = 1;
 } else {
   p_rc->next_key_frame_forced = 0;
 }

 double kf_group_err = 0;
 for (i = 0; i < rc->frames_to_key; ++i) {
   const FIRSTPASS_STATS *this_stats =
       av1_firstpass_info_peek(&twopass->firstpass_info, i);
   if (this_stats != NULL) {
     // Accumulate kf group error.
     kf_group_err += calculate_modified_err_new(
         frame_info, &firstpass_info->total_stats, this_stats,
         oxcf->rc_cfg.vbrbias, twopass->modified_error_min,
         twopass->modified_error_max);
     ++p_rc->num_stats_used_for_kf_boost;
   }
 }

 // Calculate the number of bits that should be assigned to the kf group.
 if ((twopass->bits_left > 0 && twopass->modified_error_left > 0.0) ||
     (cpi->ppi->lap_enabled && oxcf->rc_cfg.mode != AOM_Q)) {
   // Maximum number of bits for a single normal frame (not key frame).
   const int max_bits = frame_max_bits(rc, oxcf);

   // Maximum number of bits allocated to the key frame group.
   int64_t max_grp_bits;

   if (oxcf->rc_cfg.vbr_corpus_complexity_lap) {
     kf_group_avg_error =
         get_kf_group_avg_error(twopass, &cpi->twopass_frame, &first_frame,
                                start_position, rc->frames_to_key);
   }

   // Default allocation based on bits left and relative
   // complexity of the section.
   twopass->kf_group_bits =
       get_kf_group_bits(cpi, kf_group_err, kf_group_avg_error);
   // Clip based on maximum per frame rate defined by the user.
   max_grp_bits = (int64_t)max_bits * (int64_t)rc->frames_to_key;
   if (twopass->kf_group_bits > max_grp_bits)
     twopass->kf_group_bits = max_grp_bits;
 } else {
   twopass->kf_group_bits = 0;
 }
 twopass->kf_group_bits = AOMMAX(0, twopass->kf_group_bits);

 if (cpi->ppi->lap_enabled) {
   // In the case of single pass based on LAP, frames to  key may have an
   // inaccurate value, and hence should be clipped to an appropriate
   // interval.
   frames_to_key_clipped =
       (int)(MAX_KF_BITS_INTERVAL_SINGLE_PASS * cpi->framerate);

   // This variable calculates the bits allocated to kf_group with a clipped
   // frames_to_key.
   if (rc->frames_to_key > frames_to_key_clipped) {
     kf_group_bits_clipped =
         (int64_t)((double)twopass->kf_group_bits * frames_to_key_clipped /
                   rc->frames_to_key);
   }
 }

 // Reset the first pass file position.
 reset_fpf_position(&cpi->twopass_frame, start_position);

 // Scan through the kf group collating various stats used to determine
 // how many bits to spend on it.
 boost_score = get_kf_boost_score(cpi, kf_raw_err, &zero_motion_accumulator,
                                  &sr_accumulator, 0);
 reset_fpf_position(&cpi->twopass_frame, start_position);
 // Store the zero motion percentage
 twopass->kf_zeromotion_pct = (int)(zero_motion_accumulator * 100.0);

 // Calculate a section intra ratio used in setting max loop filter.
 twopass->section_intra_rating = calculate_section_intra_ratio(
     start_position, twopass->stats_buf_ctx->stats_in_end, rc->frames_to_key);

 p_rc->kf_boost = (int)boost_score;

 if (cpi->ppi->lap_enabled) {
   if (oxcf->rc_cfg.mode == AOM_Q) {
     p_rc->kf_boost = get_projected_kf_boost(cpi);
   } else {
     // TODO(any): Explore using average frame stats for AOM_Q as well.
     boost_score = get_kf_boost_score(
         cpi, kf_raw_err, &zero_motion_accumulator, &sr_accumulator, 1);
     reset_fpf_position(&cpi->twopass_frame, start_position);
     p_rc->kf_boost += (int)boost_score;
   }
 }

 // Special case for static / slide show content but don't apply
 // if the kf group is very short.
 if ((zero_motion_accumulator > STATIC_KF_GROUP_FLOAT_THRESH) &&
     (rc->frames_to_key > 8)) {
   p_rc->kf_boost = AOMMAX(p_rc->kf_boost, MIN_STATIC_KF_BOOST);
 } else {
   // Apply various clamps for min and max boost
   p_rc->kf_boost = AOMMAX(p_rc->kf_boost, (rc->frames_to_key * 3));
   p_rc->kf_boost = AOMMAX(p_rc->kf_boost, MIN_KF_BOOST);
#ifdef STRICT_RC
   p_rc->kf_boost = AOMMIN(p_rc->kf_boost, MAX_KF_BOOST);
#endif
 }

 // Work out how many bits to allocate for the key frame itself.
 // In case of LAP enabled for VBR, if the frames_to_key value is
 // very high, we calculate the bits based on a clipped value of
 // frames_to_key.
 kf_bits = calculate_boost_bits(
     AOMMIN(rc->frames_to_key, frames_to_key_clipped) - 1, p_rc->kf_boost,
     AOMMIN(twopass->kf_group_bits, kf_group_bits_clipped));
 kf_bits = adjust_boost_bits_for_target_level(cpi, rc, kf_bits,
                                              twopass->kf_group_bits, 0);

 twopass->kf_group_bits -= kf_bits;

 // Save the bits to spend on the key frame.
 gf_group->bit_allocation[0] = kf_bits;
 gf_group->update_type[0] = KF_UPDATE;

 // Note the total error score of the kf group minus the key frame itself.
 if (cpi->ppi->lap_enabled)
   // As we don't have enough stats to know the actual error of the group,
   // we assume the complexity of each frame to be equal to 1, and set the
   // error as the number of frames in the group(minus the keyframe).
   twopass->kf_group_error_left = (double)(rc->frames_to_key - 1);
 else
   twopass->kf_group_error_left = kf_group_err - kf_mod_err;

 // Adjust the count of total modified error left.
 // The count of bits left is adjusted elsewhere based on real coded frame
 // sizes.
 twopass->modified_error_left -= kf_group_err;
}

#define ARF_STATS_OUTPUT 0
#if ARF_STATS_OUTPUT
unsigned int arf_count = 0;
#endif

static int get_section_target_bandwidth(AV1_COMP *cpi) {
 AV1_COMMON *const cm = &cpi->common;
 CurrentFrame *const current_frame = &cm->current_frame;
 RATE_CONTROL *const rc = &cpi->rc;
 TWO_PASS *const twopass = &cpi->ppi->twopass;
 int64_t section_target_bandwidth;
 const int frames_left = (int)(twopass->stats_buf_ctx->total_stats->count -
                               current_frame->frame_number);
 if (cpi->ppi->lap_enabled)
   section_target_bandwidth = rc->avg_frame_bandwidth;
 else {
   section_target_bandwidth = twopass->bits_left / frames_left;
   section_target_bandwidth = AOMMIN(section_target_bandwidth, INT_MAX);
 }
 return (int)section_target_bandwidth;
}

static inline void set_twopass_params_based_on_fp_stats(
   AV1_COMP *cpi, const FIRSTPASS_STATS *this_frame_ptr) {
 if (this_frame_ptr == NULL) return;

 TWO_PASS_FRAME *twopass_frame = &cpi->twopass_frame;
 // The multiplication by 256 reverses a scaling factor of (>> 8)
 // applied when combining MB error values for the frame.
 twopass_frame->mb_av_energy = log1p(this_frame_ptr->intra_error);

 const FIRSTPASS_STATS *const total_stats =
     cpi->ppi->twopass.stats_buf_ctx->total_stats;
 if (is_fp_wavelet_energy_invalid(total_stats) == 0) {
   twopass_frame->frame_avg_haar_energy =
       log1p(this_frame_ptr->frame_avg_wavelet_energy);
 }

 // Set the frame content type flag.
 if (this_frame_ptr->intra_skip_pct >= FC_ANIMATION_THRESH)
   twopass_frame->fr_content_type = FC_GRAPHICS_ANIMATION;
 else
   twopass_frame->fr_content_type = FC_NORMAL;
}

static void process_first_pass_stats(AV1_COMP *cpi,
                                    FIRSTPASS_STATS *this_frame) {
 AV1_COMMON *const cm = &cpi->common;
 CurrentFrame *const current_frame = &cm->current_frame;
 RATE_CONTROL *const rc = &cpi->rc;
 PRIMARY_RATE_CONTROL *const p_rc = &cpi->ppi->p_rc;
 TWO_PASS *const twopass = &cpi->ppi->twopass;
 FIRSTPASS_STATS *total_stats = twopass->stats_buf_ctx->total_stats;

 if (cpi->oxcf.rc_cfg.mode != AOM_Q && current_frame->frame_number == 0 &&
     cpi->gf_frame_index == 0 && total_stats &&
     twopass->stats_buf_ctx->total_left_stats) {
   if (cpi->ppi->lap_enabled) {
     /*
      * Accumulate total_stats using available limited number of stats,
      * and assign it to total_left_stats.
      */
     *twopass->stats_buf_ctx->total_left_stats = *total_stats;
   }
   // Special case code for first frame.
   const int section_target_bandwidth = get_section_target_bandwidth(cpi);
   const double section_length =
       twopass->stats_buf_ctx->total_left_stats->count;
   const double section_error =
       twopass->stats_buf_ctx->total_left_stats->coded_error / section_length;
   const double section_intra_skip =
       twopass->stats_buf_ctx->total_left_stats->intra_skip_pct /
       section_length;
   const double section_inactive_zone =
       (twopass->stats_buf_ctx->total_left_stats->inactive_zone_rows * 2) /
       ((double)cm->mi_params.mb_rows * section_length);
   const int tmp_q = get_twopass_worst_quality(
       cpi, section_error, section_intra_skip + section_inactive_zone,
       section_target_bandwidth);

   rc->active_worst_quality = tmp_q;
   rc->ni_av_qi = tmp_q;
   p_rc->last_q[INTER_FRAME] = tmp_q;
   p_rc->avg_q = av1_convert_qindex_to_q(tmp_q, cm->seq_params->bit_depth);
   p_rc->avg_frame_qindex[INTER_FRAME] = tmp_q;
   p_rc->last_q[KEY_FRAME] = (tmp_q + cpi->oxcf.rc_cfg.best_allowed_q) / 2;
   p_rc->avg_frame_qindex[KEY_FRAME] = p_rc->last_q[KEY_FRAME];
 }

 if (cpi->twopass_frame.stats_in < twopass->stats_buf_ctx->stats_in_end) {
   *this_frame = *cpi->twopass_frame.stats_in;
   ++cpi->twopass_frame.stats_in;
 }
 set_twopass_params_based_on_fp_stats(cpi, this_frame);
}

void av1_setup_target_rate(AV1_COMP *cpi) {
 RATE_CONTROL *const rc = &cpi->rc;
 GF_GROUP *const gf_group = &cpi->ppi->gf_group;

 int target_rate = gf_group->bit_allocation[cpi->gf_frame_index];

 if (has_no_stats_stage(cpi)) {
   av1_rc_set_frame_target(cpi, target_rate, cpi->common.width,
                           cpi->common.height);
 }

 rc->base_frame_target = target_rate;
}

static void mark_flashes(FIRSTPASS_STATS *first_stats,
                        FIRSTPASS_STATS *last_stats) {
 FIRSTPASS_STATS *this_stats = first_stats, *next_stats;
 while (this_stats < last_stats - 1) {
   next_stats = this_stats + 1;
   if (next_stats->pcnt_second_ref > next_stats->pcnt_inter &&
       next_stats->pcnt_second_ref >= 0.5) {
     this_stats->is_flash = 1;
   } else {
     this_stats->is_flash = 0;
   }
   this_stats = next_stats;
 }
 // We always treat the last one as none flash.
 if (last_stats - 1 >= first_stats) {
   (last_stats - 1)->is_flash = 0;
 }
}

// Smooth-out the noise variance so it is more stable
// Returns 0 on success, -1 on memory allocation failure.
// TODO(bohanli): Use a better low-pass filter than averaging
static int smooth_filter_noise(FIRSTPASS_STATS *first_stats,
                              FIRSTPASS_STATS *last_stats) {
 int len = (int)(last_stats - first_stats);
 double *smooth_noise = aom_malloc(len * sizeof(*smooth_noise));
 if (!smooth_noise) return -1;

 for (int i = 0; i < len; i++) {
   double total_noise = 0;
   double total_wt = 0;
   for (int j = -HALF_FILT_LEN; j <= HALF_FILT_LEN; j++) {
     int idx = clamp(i + j, 0, len - 1);
     if (first_stats[idx].is_flash) continue;

     total_noise += first_stats[idx].noise_var;
     total_wt += 1.0;
   }
   if (total_wt > 0.01) {
     total_noise /= total_wt;
   } else {
     total_noise = first_stats[i].noise_var;
   }
   smooth_noise[i] = total_noise;
 }

 for (int i = 0; i < len; i++) {
   first_stats[i].noise_var = smooth_noise[i];
 }

 aom_free(smooth_noise);
 return 0;
}

// Estimate the noise variance of each frame from the first pass stats
static void estimate_noise(FIRSTPASS_STATS *first_stats,
                          FIRSTPASS_STATS *last_stats,
                          struct aom_internal_error_info *error_info) {
 FIRSTPASS_STATS *this_stats, *next_stats;
 double C1, C2, C3, noise;
 for (this_stats = first_stats + 2; this_stats < last_stats; this_stats++) {
   this_stats->noise_var = 0.0;
   // flashes tend to have high correlation of innovations, so ignore them.
   if (this_stats->is_flash || (this_stats - 1)->is_flash ||
       (this_stats - 2)->is_flash)
     continue;

   C1 = (this_stats - 1)->intra_error *
        (this_stats->intra_error - this_stats->coded_error);
   C2 = (this_stats - 2)->intra_error *
        ((this_stats - 1)->intra_error - (this_stats - 1)->coded_error);
   C3 = (this_stats - 2)->intra_error *
        (this_stats->intra_error - this_stats->sr_coded_error);
   if (C1 <= 0 || C2 <= 0 || C3 <= 0) continue;
   C1 = sqrt(C1);
   C2 = sqrt(C2);
   C3 = sqrt(C3);

   noise = (this_stats - 1)->intra_error - C1 * C2 / C3;
   noise = AOMMAX(noise, 0.01);
   this_stats->noise_var = noise;
 }

 // Copy noise from the neighbor if the noise value is not trustworthy
 for (this_stats = first_stats + 2; this_stats < last_stats; this_stats++) {
   if (this_stats->is_flash || (this_stats - 1)->is_flash ||
       (this_stats - 2)->is_flash)
     continue;
   if (this_stats->noise_var < 1.0) {
     int found = 0;
     // TODO(bohanli): consider expanding to two directions at the same time
     for (next_stats = this_stats + 1; next_stats < last_stats; next_stats++) {
       if (next_stats->is_flash || (next_stats - 1)->is_flash ||
           (next_stats - 2)->is_flash || next_stats->noise_var < 1.0)
         continue;
       found = 1;
       this_stats->noise_var = next_stats->noise_var;
       break;
     }
     if (found) continue;
     for (next_stats = this_stats - 1; next_stats >= first_stats + 2;
          next_stats--) {
       if (next_stats->is_flash || (next_stats - 1)->is_flash ||
           (next_stats - 2)->is_flash || next_stats->noise_var < 1.0)
         continue;
       this_stats->noise_var = next_stats->noise_var;
       break;
     }
   }
 }

 // copy the noise if this is a flash
 for (this_stats = first_stats + 2; this_stats < last_stats; this_stats++) {
   if (this_stats->is_flash || (this_stats - 1)->is_flash ||
       (this_stats - 2)->is_flash) {
     int found = 0;
     for (next_stats = this_stats + 1; next_stats < last_stats; next_stats++) {
       if (next_stats->is_flash || (next_stats - 1)->is_flash ||
           (next_stats - 2)->is_flash)
         continue;
       found = 1;
       this_stats->noise_var = next_stats->noise_var;
       break;
     }
     if (found) continue;
     for (next_stats = this_stats - 1; next_stats >= first_stats + 2;
          next_stats--) {
       if (next_stats->is_flash || (next_stats - 1)->is_flash ||
           (next_stats - 2)->is_flash)
         continue;
       this_stats->noise_var = next_stats->noise_var;
       break;
     }
   }
 }

 // if we are at the first 2 frames, copy the noise
 for (this_stats = first_stats;
      this_stats < first_stats + 2 && (first_stats + 2) < last_stats;
      this_stats++) {
   this_stats->noise_var = (first_stats + 2)->noise_var;
 }

 if (smooth_filter_noise(first_stats, last_stats) == -1) {
   aom_internal_error(error_info, AOM_CODEC_MEM_ERROR,
                      "Error allocating buffers in smooth_filter_noise()");
 }
}

// Estimate correlation coefficient of each frame with its previous frame.
static void estimate_coeff(FIRSTPASS_STATS *first_stats,
                          FIRSTPASS_STATS *last_stats) {
 FIRSTPASS_STATS *this_stats;
 for (this_stats = first_stats + 1; this_stats < last_stats; this_stats++) {
   const double C =
       sqrt(AOMMAX((this_stats - 1)->intra_error *
                       (this_stats->intra_error - this_stats->coded_error),
                   0.001));
   const double cor_coeff =
       C /
       AOMMAX((this_stats - 1)->intra_error - this_stats->noise_var, 0.001);

   this_stats->cor_coeff =
       cor_coeff *
       sqrt(AOMMAX((this_stats - 1)->intra_error - this_stats->noise_var,
                   0.001) /
            AOMMAX(this_stats->intra_error - this_stats->noise_var, 0.001));
   // clip correlation coefficient.
   this_stats->cor_coeff = fclamp(this_stats->cor_coeff, 0.0, 1.0);
 }
 first_stats->cor_coeff = 1.0;
}

void av1_get_second_pass_params(AV1_COMP *cpi,
                               EncodeFrameParams *const frame_params,
                               unsigned int frame_flags) {
 RATE_CONTROL *const rc = &cpi->rc;
 PRIMARY_RATE_CONTROL *const p_rc = &cpi->ppi->p_rc;
 TWO_PASS *const twopass = &cpi->ppi->twopass;
 GF_GROUP *const gf_group = &cpi->ppi->gf_group;
 const AV1EncoderConfig *const oxcf = &cpi->oxcf;

 if (cpi->use_ducky_encode &&
     cpi->ducky_encode_info.frame_info.gop_mode == DUCKY_ENCODE_GOP_MODE_RCL) {
   frame_params->frame_type = gf_group->frame_type[cpi->gf_frame_index];
   frame_params->show_frame =
       !(gf_group->update_type[cpi->gf_frame_index] == ARF_UPDATE ||
         gf_group->update_type[cpi->gf_frame_index] == INTNL_ARF_UPDATE);
   if (cpi->gf_frame_index == 0) {
     av1_tf_info_reset(&cpi->ppi->tf_info);
     av1_tf_info_filtering(&cpi->ppi->tf_info, cpi, gf_group);
   }
   return;
 }

 const FIRSTPASS_STATS *const start_pos = cpi->twopass_frame.stats_in;
 int update_total_stats = 0;

 if (is_stat_consumption_stage(cpi) && !cpi->twopass_frame.stats_in) return;

 // Check forced key frames.
 const int frames_to_next_forced_key = detect_app_forced_key(cpi);
 if (frames_to_next_forced_key == 0) {
   rc->frames_to_key = 0;
   frame_flags &= FRAMEFLAGS_KEY;
 } else if (frames_to_next_forced_key > 0 &&
            frames_to_next_forced_key < rc->frames_to_key) {
   rc->frames_to_key = frames_to_next_forced_key;
 }

 assert(cpi->twopass_frame.stats_in != NULL);
 const int update_type = gf_group->update_type[cpi->gf_frame_index];
 frame_params->frame_type = gf_group->frame_type[cpi->gf_frame_index];

 if (cpi->gf_frame_index < gf_group->size && !(frame_flags & FRAMEFLAGS_KEY)) {
   assert(cpi->gf_frame_index < gf_group->size);

   av1_setup_target_rate(cpi);

   // If this is an arf frame then we dont want to read the stats file or
   // advance the input pointer as we already have what we need.
   if (update_type == ARF_UPDATE || update_type == INTNL_ARF_UPDATE) {
     const FIRSTPASS_STATS *const this_frame_ptr =
         read_frame_stats(twopass, &cpi->twopass_frame,
                          gf_group->arf_src_offset[cpi->gf_frame_index]);
     set_twopass_params_based_on_fp_stats(cpi, this_frame_ptr);
     return;
   }
 }

 if (oxcf->rc_cfg.mode == AOM_Q)
   rc->active_worst_quality = oxcf->rc_cfg.cq_level;

 if (cpi->gf_frame_index == gf_group->size) {
   if (cpi->ppi->lap_enabled && cpi->ppi->p_rc.enable_scenecut_detection) {
     const int num_frames_to_detect_scenecut = MAX_GF_LENGTH_LAP + 1;
     const int frames_to_key = define_kf_interval(
         cpi, &twopass->firstpass_info, num_frames_to_detect_scenecut,
         /*search_start_idx=*/0);
     if (frames_to_key != -1)
       rc->frames_to_key = AOMMIN(rc->frames_to_key, frames_to_key);
   }
 }

 FIRSTPASS_STATS this_frame;
 av1_zero(this_frame);
 // call above fn
 if (is_stat_consumption_stage(cpi)) {
   if (cpi->gf_frame_index < gf_group->size || rc->frames_to_key == 0) {
     process_first_pass_stats(cpi, &this_frame);
     update_total_stats = 1;
   }
 } else {
   rc->active_worst_quality = oxcf->rc_cfg.cq_level;
 }

 // Keyframe and section processing.
 FIRSTPASS_STATS this_frame_copy;
 this_frame_copy = this_frame;
 if (rc->frames_to_key <= 0) {
   assert(rc->frames_to_key == 0);
   // Define next KF group and assign bits to it.
   frame_params->frame_type = KEY_FRAME;
   find_next_key_frame(cpi, &this_frame);
   this_frame = this_frame_copy;
 }

 if (rc->frames_to_fwd_kf <= 0)
   rc->frames_to_fwd_kf = oxcf->kf_cfg.fwd_kf_dist;

 // Define a new GF/ARF group. (Should always enter here for key frames).
 if (cpi->gf_frame_index == gf_group->size) {
   av1_tf_info_reset(&cpi->ppi->tf_info);
#if CONFIG_BITRATE_ACCURACY && !CONFIG_THREE_PASS
   vbr_rc_reset_gop_data(&cpi->vbr_rc_info);
#endif  // CONFIG_BITRATE_ACCURACY
   int max_gop_length =
       (oxcf->gf_cfg.lag_in_frames >= 32)
           ? AOMMIN(MAX_GF_INTERVAL, oxcf->gf_cfg.lag_in_frames -
                                         oxcf->algo_cfg.arnr_max_frames / 2)
           : MAX_GF_LENGTH_LAP;

   // Handle forward key frame when enabled.
   if (oxcf->kf_cfg.fwd_kf_dist > 0)
     max_gop_length = AOMMIN(rc->frames_to_fwd_kf + 1, max_gop_length);

   // Use the provided gop size in low delay setting
   if (oxcf->gf_cfg.lag_in_frames == 0) max_gop_length = rc->max_gf_interval;

   // Limit the max gop length for the last gop in 1 pass setting.
   max_gop_length = AOMMIN(max_gop_length, rc->frames_to_key);

   // Identify regions if needed.
   // TODO(bohanli): identify regions for all stats available.
   if (rc->frames_since_key == 0 || rc->frames_since_key == 1 ||
       (p_rc->frames_till_regions_update - rc->frames_since_key <
            rc->frames_to_key &&
        p_rc->frames_till_regions_update - rc->frames_since_key <
            max_gop_length + 1)) {
     // how many frames we can analyze from this frame
     int rest_frames =
         AOMMIN(rc->frames_to_key, MAX_FIRSTPASS_ANALYSIS_FRAMES);
     rest_frames =
         AOMMIN(rest_frames, (int)(twopass->stats_buf_ctx->stats_in_end -
                                   cpi->twopass_frame.stats_in +
                                   (rc->frames_since_key == 0)));
     p_rc->frames_till_regions_update = rest_frames;

     int ret;
     if (cpi->ppi->lap_enabled) {
       mark_flashes(twopass->stats_buf_ctx->stats_in_start,
                    twopass->stats_buf_ctx->stats_in_end);
       estimate_noise(twopass->stats_buf_ctx->stats_in_start,
                      twopass->stats_buf_ctx->stats_in_end, cpi->common.error);
       estimate_coeff(twopass->stats_buf_ctx->stats_in_start,
                      twopass->stats_buf_ctx->stats_in_end);
       ret = identify_regions(cpi->twopass_frame.stats_in, rest_frames,
                              (rc->frames_since_key == 0), p_rc->regions,
                              &p_rc->num_regions);
     } else {
       ret = identify_regions(
           cpi->twopass_frame.stats_in - (rc->frames_since_key == 0),
           rest_frames, 0, p_rc->regions, &p_rc->num_regions);
     }
     if (ret == -1) {
       aom_internal_error(cpi->common.error, AOM_CODEC_MEM_ERROR,
                          "Error allocating buffers in identify_regions");
     }
   }

   int cur_region_idx =
       find_regions_index(p_rc->regions, p_rc->num_regions,
                          rc->frames_since_key - p_rc->regions_offset);
   if ((cur_region_idx >= 0 &&
        p_rc->regions[cur_region_idx].type == SCENECUT_REGION) ||
       rc->frames_since_key == 0) {
     // If we start from a scenecut, then the last GOP's arf boost is not
     // needed for this GOP.
     cpi->ppi->gf_state.arf_gf_boost_lst = 0;
   }

   int need_gf_len = 1;
#if CONFIG_THREE_PASS
   if (cpi->third_pass_ctx && oxcf->pass == AOM_RC_THIRD_PASS) {
     // set up bitstream to read
     if (!cpi->third_pass_ctx->input_file_name && oxcf->two_pass_output) {
       cpi->third_pass_ctx->input_file_name = oxcf->two_pass_output;
     }
     av1_open_second_pass_log(cpi, 1);
     THIRD_PASS_GOP_INFO *gop_info = &cpi->third_pass_ctx->gop_info;
     // Read in GOP information from the second pass file.
     av1_read_second_pass_gop_info(cpi->second_pass_log_stream, gop_info,
                                   cpi->common.error);
#if CONFIG_BITRATE_ACCURACY
     TPL_INFO *tpl_info;
     AOM_CHECK_MEM_ERROR(cpi->common.error, tpl_info,
                         aom_malloc(sizeof(*tpl_info)));
     av1_read_tpl_info(tpl_info, cpi->second_pass_log_stream,
                       cpi->common.error);
     aom_free(tpl_info);
#if CONFIG_THREE_PASS
     // TODO(angiebird): Put this part into a func
     cpi->vbr_rc_info.cur_gop_idx++;
#endif  // CONFIG_THREE_PASS
#endif  // CONFIG_BITRATE_ACCURACY
     // Read in third_pass_info from the bitstream.
     av1_set_gop_third_pass(cpi->third_pass_ctx);
     // Read in per-frame info from second-pass encoding
     av1_read_second_pass_per_frame_info(
         cpi->second_pass_log_stream, cpi->third_pass_ctx->frame_info,
         gop_info->num_frames, cpi->common.error);

     p_rc->cur_gf_index = 0;
     p_rc->gf_intervals[0] = cpi->third_pass_ctx->gop_info.gf_length;
     need_gf_len = 0;
   }
#endif  // CONFIG_THREE_PASS

   if (need_gf_len) {
     // If we cannot obtain GF group length from second_pass_file
     // TODO(jingning): Resolve the redundant calls here.
     if (rc->intervals_till_gf_calculate_due == 0 || 1) {
       calculate_gf_length(cpi, max_gop_length, MAX_NUM_GF_INTERVALS);
     }

     if (max_gop_length > 16 && oxcf->algo_cfg.enable_tpl_model &&
         oxcf->gf_cfg.lag_in_frames >= 32 &&
         cpi->sf.tpl_sf.gop_length_decision_method != 3) {
       int this_idx = rc->frames_since_key +
                      p_rc->gf_intervals[p_rc->cur_gf_index] -
                      p_rc->regions_offset - 1;
       int this_region =
           find_regions_index(p_rc->regions, p_rc->num_regions, this_idx);
       int next_region =
           find_regions_index(p_rc->regions, p_rc->num_regions, this_idx + 1);
       // TODO(angiebird): Figure out why this_region and next_region are -1 in
       // unit test like AltRefFramePresenceTestLarge (aomedia:3134)
       int is_last_scenecut =
           p_rc->gf_intervals[p_rc->cur_gf_index] >= rc->frames_to_key ||
           (this_region != -1 &&
            p_rc->regions[this_region].type == SCENECUT_REGION) ||
           (next_region != -1 &&
            p_rc->regions[next_region].type == SCENECUT_REGION);

       int ori_gf_int = p_rc->gf_intervals[p_rc->cur_gf_index];

       if (p_rc->gf_intervals[p_rc->cur_gf_index] > 16 &&
           rc->min_gf_interval <= 16) {
         // The calculate_gf_length function is previously used with
         // max_gop_length = 32 with look-ahead gf intervals.
         define_gf_group(cpi, frame_params, 0);
         av1_tf_info_filtering(&cpi->ppi->tf_info, cpi, gf_group);
         this_frame = this_frame_copy;

         if (is_shorter_gf_interval_better(cpi, frame_params)) {
           // A shorter gf interval is better.
           // TODO(jingning): Remove redundant computations here.
           max_gop_length = 16;
           calculate_gf_length(cpi, max_gop_length, 1);
           if (is_last_scenecut &&
               (ori_gf_int - p_rc->gf_intervals[p_rc->cur_gf_index] < 4)) {
             p_rc->gf_intervals[p_rc->cur_gf_index] = ori_gf_int;
           }
         }
       }
     }
   }

   define_gf_group(cpi, frame_params, 0);

   if (gf_group->update_type[cpi->gf_frame_index] != ARF_UPDATE &&
       rc->frames_since_key > 0)
     process_first_pass_stats(cpi, &this_frame);

   define_gf_group(cpi, frame_params, 1);

#if CONFIG_THREE_PASS
   // write gop info if needed for third pass. Per-frame info is written after
   // each frame is encoded.
   av1_write_second_pass_gop_info(cpi);
#endif  // CONFIG_THREE_PASS

   av1_tf_info_filtering(&cpi->ppi->tf_info, cpi, gf_group);

   rc->frames_till_gf_update_due = p_rc->baseline_gf_interval;
   assert(cpi->gf_frame_index == 0);
#if ARF_STATS_OUTPUT
   {
     FILE *fpfile;
     fpfile = fopen("arf.stt", "a");
     ++arf_count;
     fprintf(fpfile, "%10d %10d %10d %10d %10d\n",
             cpi->common.current_frame.frame_number,
             rc->frames_till_gf_update_due, cpi->ppi->p_rc.kf_boost, arf_count,
             p_rc->gfu_boost);

     fclose(fpfile);
   }
#endif
 }
 assert(cpi->gf_frame_index < gf_group->size);

 if (gf_group->update_type[cpi->gf_frame_index] == ARF_UPDATE ||
     gf_group->update_type[cpi->gf_frame_index] == INTNL_ARF_UPDATE) {
   reset_fpf_position(&cpi->twopass_frame, start_pos);

   const FIRSTPASS_STATS *const this_frame_ptr =
       read_frame_stats(twopass, &cpi->twopass_frame,
                        gf_group->arf_src_offset[cpi->gf_frame_index]);
   set_twopass_params_based_on_fp_stats(cpi, this_frame_ptr);
 } else {
   // Back up this frame's stats for updating total stats during post encode.
   cpi->twopass_frame.this_frame = update_total_stats ? start_pos : NULL;
 }

 frame_params->frame_type = gf_group->frame_type[cpi->gf_frame_index];
 av1_setup_target_rate(cpi);
}

void av1_init_second_pass(AV1_COMP *cpi) {
 const AV1EncoderConfig *const oxcf = &cpi->oxcf;
 TWO_PASS *const twopass = &cpi->ppi->twopass;
 FRAME_INFO *const frame_info = &cpi->frame_info;
 double frame_rate;
 FIRSTPASS_STATS *stats;

 if (!twopass->stats_buf_ctx->stats_in_end) return;

 mark_flashes(twopass->stats_buf_ctx->stats_in_start,
              twopass->stats_buf_ctx->stats_in_end);
 estimate_noise(twopass->stats_buf_ctx->stats_in_start,
                twopass->stats_buf_ctx->stats_in_end, cpi->common.error);
 estimate_coeff(twopass->stats_buf_ctx->stats_in_start,
                twopass->stats_buf_ctx->stats_in_end);

 stats = twopass->stats_buf_ctx->total_stats;

 *stats = *twopass->stats_buf_ctx->stats_in_end;
 *twopass->stats_buf_ctx->total_left_stats = *stats;

 frame_rate = 10000000.0 * stats->count / stats->duration;
 // Each frame can have a different duration, as the frame rate in the source
 // isn't guaranteed to be constant. The frame rate prior to the first frame
 // encoded in the second pass is a guess. However, the sum duration is not.
 // It is calculated based on the actual durations of all frames from the
 // first pass.
 av1_new_framerate(cpi, frame_rate);
 twopass->bits_left =
     (int64_t)(stats->duration * oxcf->rc_cfg.target_bandwidth / 10000000.0);

#if CONFIG_BITRATE_ACCURACY
 av1_vbr_rc_init(&cpi->vbr_rc_info, twopass->bits_left,
                 (int)round(stats->count));
#endif

#if CONFIG_RATECTRL_LOG
 rc_log_init(&cpi->rc_log);
#endif

 // This variable monitors how far behind the second ref update is lagging.
 twopass->sr_update_lag = 1;

 // Scan the first pass file and calculate a modified total error based upon
 // the bias/power function used to allocate bits.
 {
   const double avg_error =
       stats->coded_error / DOUBLE_DIVIDE_CHECK(stats->count);
   const FIRSTPASS_STATS *s = cpi->twopass_frame.stats_in;
   double modified_error_total = 0.0;
   twopass->modified_error_min =
       (avg_error * oxcf->rc_cfg.vbrmin_section) / 100;
   twopass->modified_error_max =
       (avg_error * oxcf->rc_cfg.vbrmax_section) / 100;
   while (s < twopass->stats_buf_ctx->stats_in_end) {
     modified_error_total +=
         calculate_modified_err(frame_info, twopass, oxcf, s);
     ++s;
   }
   twopass->modified_error_left = modified_error_total;
 }

 // Reset the vbr bits off target counters
 cpi->ppi->p_rc.vbr_bits_off_target = 0;
 cpi->ppi->p_rc.vbr_bits_off_target_fast = 0;

 cpi->ppi->p_rc.rate_error_estimate = 0;

 // Static sequence monitor variables.
 twopass->kf_zeromotion_pct = 100;
 twopass->last_kfgroup_zeromotion_pct = 100;

 // Initialize bits per macro_block estimate correction factor.
 twopass->bpm_factor = 1.0;
 // Initialize actual and target bits counters for ARF groups so that
 // at the start we have a neutral bpm adjustment.
 twopass->rolling_arf_group_target_bits = 1;
 twopass->rolling_arf_group_actual_bits = 1;
}

void av1_init_single_pass_lap(AV1_COMP *cpi) {
 TWO_PASS *const twopass = &cpi->ppi->twopass;

 if (!twopass->stats_buf_ctx->stats_in_end) return;

 // This variable monitors how far behind the second ref update is lagging.
 twopass->sr_update_lag = 1;

 twopass->bits_left = 0;
 twopass->modified_error_min = 0.0;
 twopass->modified_error_max = 0.0;
 twopass->modified_error_left = 0.0;

 // Reset the vbr bits off target counters
 cpi->ppi->p_rc.vbr_bits_off_target = 0;
 cpi->ppi->p_rc.vbr_bits_off_target_fast = 0;

 cpi->ppi->p_rc.rate_error_estimate = 0;

 // Static sequence monitor variables.
 twopass->kf_zeromotion_pct = 100;
 twopass->last_kfgroup_zeromotion_pct = 100;

 // Initialize bits per macro_block estimate correction factor.
 twopass->bpm_factor = 1.0;
 // Initialize actual and target bits counters for ARF groups so that
 // at the start we have a neutral bpm adjustment.
 twopass->rolling_arf_group_target_bits = 1;
 twopass->rolling_arf_group_actual_bits = 1;
}

#define MINQ_ADJ_LIMIT 48
#define MINQ_ADJ_LIMIT_CQ 20
#define HIGH_UNDERSHOOT_RATIO 2
void av1_twopass_postencode_update(AV1_COMP *cpi) {
 TWO_PASS *const twopass = &cpi->ppi->twopass;
 RATE_CONTROL *const rc = &cpi->rc;
 PRIMARY_RATE_CONTROL *const p_rc = &cpi->ppi->p_rc;
 const RateControlCfg *const rc_cfg = &cpi->oxcf.rc_cfg;

 // Increment the stats_in pointer.
 if (is_stat_consumption_stage(cpi) &&
     !(cpi->use_ducky_encode && cpi->ducky_encode_info.frame_info.gop_mode ==
                                    DUCKY_ENCODE_GOP_MODE_RCL) &&
     (cpi->gf_frame_index < cpi->ppi->gf_group.size ||
      rc->frames_to_key == 0)) {
   const int update_type = cpi->ppi->gf_group.update_type[cpi->gf_frame_index];
   if (update_type != ARF_UPDATE && update_type != INTNL_ARF_UPDATE) {
     FIRSTPASS_STATS this_frame;
     assert(cpi->twopass_frame.stats_in >
            twopass->stats_buf_ctx->stats_in_start);
     --cpi->twopass_frame.stats_in;
     if (cpi->ppi->lap_enabled) {
       input_stats_lap(twopass, &cpi->twopass_frame, &this_frame);
     } else {
       input_stats(twopass, &cpi->twopass_frame, &this_frame);
     }
   } else if (cpi->ppi->lap_enabled) {
     cpi->twopass_frame.stats_in = twopass->stats_buf_ctx->stats_in_start;
   }
 }

 // VBR correction is done through rc->vbr_bits_off_target. Based on the
 // sign of this value, a limited % adjustment is made to the target rate
 // of subsequent frames, to try and push it back towards 0. This method
 // is designed to prevent extreme behaviour at the end of a clip
 // or group of frames.
 p_rc->vbr_bits_off_target += rc->base_frame_target - rc->projected_frame_size;
 twopass->bits_left = AOMMAX(twopass->bits_left - rc->base_frame_target, 0);

 if (cpi->do_update_vbr_bits_off_target_fast) {
   // Subtract current frame's fast_extra_bits.
   p_rc->vbr_bits_off_target_fast -= rc->frame_level_fast_extra_bits;
   rc->frame_level_fast_extra_bits = 0;
 }

 // Target vs actual bits for this arf group.
 if (twopass->rolling_arf_group_target_bits >
     INT_MAX - rc->base_frame_target) {
   twopass->rolling_arf_group_target_bits = INT_MAX;
 } else {
   twopass->rolling_arf_group_target_bits += rc->base_frame_target;
 }
 twopass->rolling_arf_group_actual_bits += rc->projected_frame_size;

 // Calculate the pct rc error.
 if (p_rc->total_actual_bits) {
   p_rc->rate_error_estimate =
       (int)((p_rc->vbr_bits_off_target * 100) / p_rc->total_actual_bits);
   p_rc->rate_error_estimate = clamp(p_rc->rate_error_estimate, -100, 100);
 } else {
   p_rc->rate_error_estimate = 0;
 }

#if CONFIG_FPMT_TEST
 /* The variables temp_vbr_bits_off_target, temp_bits_left,
  * temp_rolling_arf_group_target_bits, temp_rolling_arf_group_actual_bits
  * temp_rate_error_estimate are introduced for quality simulation purpose,
  * it retains the value previous to the parallel encode frames. The
  * variables are updated based on the update flag.
  *
  * If there exist show_existing_frames between parallel frames, then to
  * retain the temp state do not update it. */
 const int simulate_parallel_frame =
     cpi->ppi->fpmt_unit_test_cfg == PARALLEL_SIMULATION_ENCODE;
 int show_existing_between_parallel_frames =
     (cpi->ppi->gf_group.update_type[cpi->gf_frame_index] ==
          INTNL_OVERLAY_UPDATE &&
      cpi->ppi->gf_group.frame_parallel_level[cpi->gf_frame_index + 1] == 2);

 if (cpi->do_frame_data_update && !show_existing_between_parallel_frames &&
     simulate_parallel_frame) {
   cpi->ppi->p_rc.temp_vbr_bits_off_target = p_rc->vbr_bits_off_target;
   cpi->ppi->p_rc.temp_bits_left = twopass->bits_left;
   cpi->ppi->p_rc.temp_rolling_arf_group_target_bits =
       twopass->rolling_arf_group_target_bits;
   cpi->ppi->p_rc.temp_rolling_arf_group_actual_bits =
       twopass->rolling_arf_group_actual_bits;
   cpi->ppi->p_rc.temp_rate_error_estimate = p_rc->rate_error_estimate;
 }
#endif
 // Update the active best quality pyramid.
 if (!rc->is_src_frame_alt_ref) {
   const int pyramid_level =
       cpi->ppi->gf_group.layer_depth[cpi->gf_frame_index];
   int i;
   for (i = pyramid_level; i <= MAX_ARF_LAYERS; ++i) {
     p_rc->active_best_quality[i] = cpi->common.quant_params.base_qindex;
#if CONFIG_TUNE_VMAF
     if (cpi->vmaf_info.original_qindex != -1 &&
         (cpi->oxcf.tune_cfg.tuning >= AOM_TUNE_VMAF_WITH_PREPROCESSING &&
          cpi->oxcf.tune_cfg.tuning <= AOM_TUNE_VMAF_NEG_MAX_GAIN)) {
       p_rc->active_best_quality[i] = cpi->vmaf_info.original_qindex;
     }
#endif
   }
 }

#if 0
 {
   AV1_COMMON *cm = &cpi->common;
   FILE *fpfile;
   fpfile = fopen("details.stt", "a");
   fprintf(fpfile,
           "%10d %10d %10d %10" PRId64 " %10" PRId64
           " %10d %10d %10d %10.4lf %10.4lf %10.4lf %10.4lf\n",
           cm->current_frame.frame_number, rc->base_frame_target,
           rc->projected_frame_size, rc->total_actual_bits,
           rc->vbr_bits_off_target, p_rc->rate_error_estimate,
           twopass->rolling_arf_group_target_bits,
           twopass->rolling_arf_group_actual_bits,
           (double)twopass->rolling_arf_group_actual_bits /
               (double)twopass->rolling_arf_group_target_bits,
           twopass->bpm_factor,
           av1_convert_qindex_to_q(cpi->common.quant_params.base_qindex,
                                   cm->seq_params->bit_depth),
           av1_convert_qindex_to_q(rc->active_worst_quality,
                                   cm->seq_params->bit_depth));
   fclose(fpfile);
 }
#endif

 if (cpi->common.current_frame.frame_type != KEY_FRAME) {
   twopass->kf_group_bits -= rc->base_frame_target;
   twopass->last_kfgroup_zeromotion_pct = twopass->kf_zeromotion_pct;
 }
 twopass->kf_group_bits = AOMMAX(twopass->kf_group_bits, 0);

 // If the rate control is drifting consider adjustment to min or maxq.
 if ((rc_cfg->mode != AOM_Q) && !cpi->rc.is_src_frame_alt_ref &&
     (p_rc->rolling_target_bits > 0)) {
   int minq_adj_limit;
   int maxq_adj_limit;
   minq_adj_limit =
       (rc_cfg->mode == AOM_CQ ? MINQ_ADJ_LIMIT_CQ : MINQ_ADJ_LIMIT);
   maxq_adj_limit = rc->worst_quality - rc->active_worst_quality;

   // Undershoot
   if ((rc_cfg->under_shoot_pct < 100) &&
       (p_rc->rolling_actual_bits < p_rc->rolling_target_bits)) {
     int pct_error =
         ((p_rc->rolling_target_bits - p_rc->rolling_actual_bits) * 100) /
         p_rc->rolling_target_bits;

     if ((pct_error >= rc_cfg->under_shoot_pct) &&
         (p_rc->rate_error_estimate > 0)) {
       twopass->extend_minq += 1;
     }
     twopass->extend_maxq -= 1;
     // Overshoot
   } else if ((rc_cfg->over_shoot_pct < 100) &&
              (p_rc->rolling_actual_bits > p_rc->rolling_target_bits)) {
     int pct_error =
         ((p_rc->rolling_actual_bits - p_rc->rolling_target_bits) * 100) /
         p_rc->rolling_target_bits;

     pct_error = clamp(pct_error, 0, 100);
     if ((pct_error >= rc_cfg->over_shoot_pct) &&
         (p_rc->rate_error_estimate < 0)) {
       twopass->extend_maxq += 1;
     }
     twopass->extend_minq -= 1;
   } else {
     // Adjustment for extreme local overshoot.
     // Only applies when normal adjustment above is not used (e.g.
     // when threshold is set to 100).
     if (rc->projected_frame_size > (2 * rc->base_frame_target) &&
         rc->projected_frame_size > (2 * rc->avg_frame_bandwidth))
       ++twopass->extend_maxq;
     // Unwind extreme overshoot adjustment.
     else if (p_rc->rolling_target_bits > p_rc->rolling_actual_bits)
       --twopass->extend_maxq;
   }
   twopass->extend_minq =
       clamp(twopass->extend_minq, -minq_adj_limit, minq_adj_limit);
   twopass->extend_maxq = clamp(twopass->extend_maxq, 0, maxq_adj_limit);

   // If there is a big and undexpected undershoot then feed the extra
   // bits back in quickly. One situation where this may happen is if a
   // frame is unexpectedly almost perfectly predicted by the ARF or GF
   // but not very well predcited by the previous frame.
   if (!frame_is_kf_gf_arf(cpi) && !cpi->rc.is_src_frame_alt_ref) {
     int fast_extra_thresh = rc->base_frame_target / HIGH_UNDERSHOOT_RATIO;
     if (rc->projected_frame_size < fast_extra_thresh) {
       p_rc->vbr_bits_off_target_fast +=
           fast_extra_thresh - rc->projected_frame_size;
       p_rc->vbr_bits_off_target_fast =
           AOMMIN(p_rc->vbr_bits_off_target_fast,
                  (4 * (int64_t)rc->avg_frame_bandwidth));
     }
   }

#if CONFIG_FPMT_TEST
   if (cpi->do_frame_data_update && !show_existing_between_parallel_frames &&
       simulate_parallel_frame) {
     cpi->ppi->p_rc.temp_vbr_bits_off_target_fast =
         p_rc->vbr_bits_off_target_fast;
     cpi->ppi->p_rc.temp_extend_minq = twopass->extend_minq;
     cpi->ppi->p_rc.temp_extend_maxq = twopass->extend_maxq;
   }
#endif
 }

 // Update the frame probabilities obtained from parallel encode frames
 FrameProbInfo *const frame_probs = &cpi->ppi->frame_probs;
#if CONFIG_FPMT_TEST
 /* The variable temp_active_best_quality is introduced only for quality
  * simulation purpose, it retains the value previous to the parallel
  * encode frames. The variable is updated based on the update flag.
  *
  * If there exist show_existing_frames between parallel frames, then to
  * retain the temp state do not update it. */
 if (cpi->do_frame_data_update && !show_existing_between_parallel_frames &&
     simulate_parallel_frame) {
   int i;
   const int pyramid_level =
       cpi->ppi->gf_group.layer_depth[cpi->gf_frame_index];
   if (!rc->is_src_frame_alt_ref) {
     for (i = pyramid_level; i <= MAX_ARF_LAYERS; ++i)
       cpi->ppi->p_rc.temp_active_best_quality[i] =
           p_rc->active_best_quality[i];
   }
 }

 // Update the frame probabilities obtained from parallel encode frames
 FrameProbInfo *const temp_frame_probs_simulation =
     simulate_parallel_frame ? &cpi->ppi->temp_frame_probs_simulation
                             : frame_probs;
 FrameProbInfo *const temp_frame_probs =
     simulate_parallel_frame ? &cpi->ppi->temp_frame_probs : NULL;
#endif
 int i, j, loop;
 // Sequentially do average on temp_frame_probs_simulation which holds
 // probabilities of last frame before parallel encode
 for (loop = 0; loop <= cpi->num_frame_recode; loop++) {
   // Sequentially update tx_type_probs
   if (cpi->do_update_frame_probs_txtype[loop] &&
       (cpi->ppi->gf_group.frame_parallel_level[cpi->gf_frame_index] > 0)) {
     const FRAME_UPDATE_TYPE update_type =
         get_frame_update_type(&cpi->ppi->gf_group, cpi->gf_frame_index);
     for (i = 0; i < TX_SIZES_ALL; i++) {
       int left = 1024;

       for (j = TX_TYPES - 1; j >= 0; j--) {
         const int new_prob =
             cpi->frame_new_probs[loop].tx_type_probs[update_type][i][j];
#if CONFIG_FPMT_TEST
         int prob =
             (temp_frame_probs_simulation->tx_type_probs[update_type][i][j] +
              new_prob) >>
             1;
         left -= prob;
         if (j == 0) prob += left;
         temp_frame_probs_simulation->tx_type_probs[update_type][i][j] = prob;
#else
         int prob =
             (frame_probs->tx_type_probs[update_type][i][j] + new_prob) >> 1;
         left -= prob;
         if (j == 0) prob += left;
         frame_probs->tx_type_probs[update_type][i][j] = prob;
#endif
       }
     }
   }

   // Sequentially update obmc_probs
   if (cpi->do_update_frame_probs_obmc[loop] &&
       cpi->ppi->gf_group.frame_parallel_level[cpi->gf_frame_index] > 0) {
     const FRAME_UPDATE_TYPE update_type =
         get_frame_update_type(&cpi->ppi->gf_group, cpi->gf_frame_index);

     for (i = 0; i < BLOCK_SIZES_ALL; i++) {
       const int new_prob =
           cpi->frame_new_probs[loop].obmc_probs[update_type][i];
#if CONFIG_FPMT_TEST
       temp_frame_probs_simulation->obmc_probs[update_type][i] =
           (temp_frame_probs_simulation->obmc_probs[update_type][i] +
            new_prob) >>
           1;
#else
       frame_probs->obmc_probs[update_type][i] =
           (frame_probs->obmc_probs[update_type][i] + new_prob) >> 1;
#endif
     }
   }

   // Sequentially update warped_probs
   if (cpi->do_update_frame_probs_warp[loop] &&
       cpi->ppi->gf_group.frame_parallel_level[cpi->gf_frame_index] > 0) {
     const FRAME_UPDATE_TYPE update_type =
         get_frame_update_type(&cpi->ppi->gf_group, cpi->gf_frame_index);
     const int new_prob = cpi->frame_new_probs[loop].warped_probs[update_type];
#if CONFIG_FPMT_TEST
     temp_frame_probs_simulation->warped_probs[update_type] =
         (temp_frame_probs_simulation->warped_probs[update_type] + new_prob) >>
         1;
#else
     frame_probs->warped_probs[update_type] =
         (frame_probs->warped_probs[update_type] + new_prob) >> 1;
#endif
   }

   // Sequentially update switchable_interp_probs
   if (cpi->do_update_frame_probs_interpfilter[loop] &&
       cpi->ppi->gf_group.frame_parallel_level[cpi->gf_frame_index] > 0) {
     const FRAME_UPDATE_TYPE update_type =
         get_frame_update_type(&cpi->ppi->gf_group, cpi->gf_frame_index);

     for (i = 0; i < SWITCHABLE_FILTER_CONTEXTS; i++) {
       int left = 1536;

       for (j = SWITCHABLE_FILTERS - 1; j >= 0; j--) {
         const int new_prob = cpi->frame_new_probs[loop]
                                  .switchable_interp_probs[update_type][i][j];
#if CONFIG_FPMT_TEST
         int prob = (temp_frame_probs_simulation
                         ->switchable_interp_probs[update_type][i][j] +
                     new_prob) >>
                    1;
         left -= prob;
         if (j == 0) prob += left;

         temp_frame_probs_simulation
             ->switchable_interp_probs[update_type][i][j] = prob;
#else
         int prob = (frame_probs->switchable_interp_probs[update_type][i][j] +
                     new_prob) >>
                    1;
         left -= prob;
         if (j == 0) prob += left;
         frame_probs->switchable_interp_probs[update_type][i][j] = prob;
#endif
       }
     }
   }
 }

#if CONFIG_FPMT_TEST
 // Copying temp_frame_probs_simulation to temp_frame_probs based on
 // the flag
 if (cpi->do_frame_data_update &&
     cpi->ppi->gf_group.frame_parallel_level[cpi->gf_frame_index] > 0 &&
     simulate_parallel_frame) {
   for (int update_type_idx = 0; update_type_idx < FRAME_UPDATE_TYPES;
        update_type_idx++) {
     for (i = 0; i < BLOCK_SIZES_ALL; i++) {
       temp_frame_probs->obmc_probs[update_type_idx][i] =
           temp_frame_probs_simulation->obmc_probs[update_type_idx][i];
     }
     temp_frame_probs->warped_probs[update_type_idx] =
         temp_frame_probs_simulation->warped_probs[update_type_idx];
     for (i = 0; i < TX_SIZES_ALL; i++) {
       for (j = 0; j < TX_TYPES; j++) {
         temp_frame_probs->tx_type_probs[update_type_idx][i][j] =
             temp_frame_probs_simulation->tx_type_probs[update_type_idx][i][j];
       }
     }
     for (i = 0; i < SWITCHABLE_FILTER_CONTEXTS; i++) {
       for (j = 0; j < SWITCHABLE_FILTERS; j++) {
         temp_frame_probs->switchable_interp_probs[update_type_idx][i][j] =
             temp_frame_probs_simulation
                 ->switchable_interp_probs[update_type_idx][i][j];
       }
     }
   }
 }
#endif
 // Update framerate obtained from parallel encode frames
 if (cpi->common.show_frame &&
     cpi->ppi->gf_group.frame_parallel_level[cpi->gf_frame_index] > 0)
   cpi->framerate = cpi->new_framerate;
#if CONFIG_FPMT_TEST
 // SIMULATION PURPOSE
 int show_existing_between_parallel_frames_cndn =
     (cpi->ppi->gf_group.update_type[cpi->gf_frame_index] ==
          INTNL_OVERLAY_UPDATE &&
      cpi->ppi->gf_group.frame_parallel_level[cpi->gf_frame_index + 1] == 2);
 if (cpi->common.show_frame && !show_existing_between_parallel_frames_cndn &&
     cpi->do_frame_data_update && simulate_parallel_frame)
   cpi->temp_framerate = cpi->framerate;
#endif
}