tor-browser

cbs.h (17308B)

---

/*
* This file is part of FFmpeg.
*
* FFmpeg is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* FFmpeg is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with FFmpeg; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/

#ifndef AVCODEC_CBS_H
#define AVCODEC_CBS_H

#include <stddef.h>
#include <stdint.h>

#include "libavutil/buffer.h"

#include "codec_id.h"
#include "codec_par.h"
#include "defs.h"
#include "packet.h"


/*
* This defines a framework for converting between a coded bitstream
* and structures defining all individual syntax elements found in
* such a stream.
*
* Conversion in both directions is possible.  Given a coded bitstream
* (any meaningful fragment), it can be parsed and decomposed into
* syntax elements stored in a set of codec-specific structures.
* Similarly, given a set of those same codec-specific structures the
* syntax elements can be serialised and combined to create a coded
* bitstream.
*/

struct AVCodecContext;
struct CodedBitstreamType;

/**
* The codec-specific type of a bitstream unit.
*
* AV1: obu_type
* H.264 / AVC: nal_unit_type
* H.265 / HEVC: nal_unit_type
* JPEG: marker value (without 0xff prefix)
* MPEG-2: start code value (without prefix)
* VP9: unused, set to zero (every unit is a frame)
*/
typedef uint32_t CodedBitstreamUnitType;

/**
* Coded bitstream unit structure.
*
* A bitstream unit the smallest element of a bitstream which
* is meaningful on its own.  For example, an H.264 NAL unit.
*
* See the codec-specific header for the meaning of this for any
* particular codec.
*/
typedef struct CodedBitstreamUnit {
   /**
    * Codec-specific type of this unit.
    */
   CodedBitstreamUnitType type;

   /**
    * Pointer to the directly-parsable bitstream form of this unit.
    *
    * May be NULL if the unit currently only exists in decomposed form.
    */
   uint8_t *data;
   /**
    * The number of bytes in the bitstream (including any padding bits
    * in the final byte).
    */
   size_t   data_size;
   /**
    * The number of bits which should be ignored in the final byte.
    *
    * This supports non-byte-aligned bitstreams.
    */
   size_t   data_bit_padding;
   /**
    * A reference to the buffer containing data.
    *
    * Must be set if data is not NULL.
    */
   AVBufferRef *data_ref;

   /**
    * Pointer to the decomposed form of this unit.
    *
    * The type of this structure depends on both the codec and the
    * type of this unit.  May be NULL if the unit only exists in
    * bitstream form.
    */
   void *content;
   /**
    * If content is reference counted, a RefStruct reference backing content.
    * NULL if content is not reference counted.
    */
   void *content_ref;
} CodedBitstreamUnit;

/**
* Coded bitstream fragment structure, combining one or more units.
*
* This is any sequence of units.  It need not form some greater whole,
* though in many cases it will.  For example, an H.264 access unit,
* which is composed of a sequence of H.264 NAL units.
*/
typedef struct CodedBitstreamFragment {
   /**
    * Pointer to the bitstream form of this fragment.
    *
    * May be NULL if the fragment only exists as component units.
    */
   uint8_t *data;
   /**
    * The number of bytes in the bitstream.
    *
    * The number of bytes in the bitstream (including any padding bits
    * in the final byte).
    */
   size_t   data_size;
   /**
    * The number of bits which should be ignored in the final byte.
    */
   size_t data_bit_padding;
   /**
    * A reference to the buffer containing data.
    *
    * Must be set if data is not NULL.
    */
   AVBufferRef *data_ref;

   /**
    * Number of units in this fragment.
    *
    * This may be zero if the fragment only exists in bitstream form
    * and has not been decomposed.
    */
   int              nb_units;

   /**
    * Number of allocated units.
    *
    * Must always be >= nb_units; designed for internal use by cbs.
    */
    int             nb_units_allocated;

   /**
    * Pointer to an array of units of length nb_units_allocated.
    * Only the first nb_units are valid.
    *
    * Must be NULL if nb_units_allocated is zero.
    */
   CodedBitstreamUnit *units;
} CodedBitstreamFragment;


struct CodedBitstreamContext;
struct GetBitContext;
struct PutBitContext;

/**
* Callback type for read tracing.
*
* @param ctx         User-set trace context.
* @param gbc         A GetBitContext set at the start of the syntax
*                    element.  This is a copy, the callee does not
*                    need to preserve it.
* @param length      Length in bits of the syntax element.
* @param name        String name of the syntax elements.
* @param subscripts  If the syntax element is an array, a pointer to
*                    an array of subscripts into the array.
* @param value       Parsed value of the syntax element.
*/
typedef void (*CBSTraceReadCallback)(void *trace_context,
                                    struct GetBitContext *gbc,
                                    int start_position,
                                    const char *name,
                                    const int *subscripts,
                                    int64_t value);

/**
* Callback type for write tracing.
*
* @param ctx         User-set trace context.
* @param pbc         A PutBitContext set at the end of the syntax
*                    element.  The user must not modify this, but may
*                    inspect it to determine state.
* @param length      Length in bits of the syntax element.
* @param name        String name of the syntax elements.
* @param subscripts  If the syntax element is an array, a pointer to
*                    an array of subscripts into the array.
* @param value       Written value of the syntax element.
*/
typedef void (*CBSTraceWriteCallback)(void *trace_context,
                                     struct PutBitContext *pbc,
                                     int start_position,
                                     const char *name,
                                     const int *subscripts,
                                     int64_t value);

/**
* Context structure for coded bitstream operations.
*/
typedef struct CodedBitstreamContext {
   /**
    * Logging context to be passed to all av_log() calls associated
    * with this context.
    */
   void *log_ctx;

   /**
    * Internal codec-specific hooks.
    */
   const struct CodedBitstreamType *codec;

   /**
    * Internal codec-specific data.
    *
    * This contains any information needed when reading/writing
    * bitsteams which will not necessarily be present in a fragment.
    * For example, for H.264 it contains all currently visible
    * parameter sets - they are required to determine the bitstream
    * syntax but need not be present in every access unit.
    */
   void *priv_data;

   /**
    * Array of unit types which should be decomposed when reading.
    *
    * Types not in this list will be available in bitstream form only.
    * If NULL, all supported types will be decomposed.
    */
   const CodedBitstreamUnitType *decompose_unit_types;
   /**
    * Length of the decompose_unit_types array.
    */
   int nb_decompose_unit_types;

   /**
    * Enable trace output during read/write operations.
    */
   int trace_enable;
   /**
    * Log level to use for default trace output.
    *
    * From AV_LOG_*; defaults to AV_LOG_TRACE.
    */
   int trace_level;
   /**
    * User context pointer to pass to trace callbacks.
    */
   void *trace_context;
   /**
    * Callback for read tracing.
    *
    * If tracing is enabled then this is called once for each syntax
    * element parsed.
    */
   CBSTraceReadCallback  trace_read_callback;
   /**
    * Callback for write tracing.
    *
    * If tracing is enabled then this is called once for each syntax
    * element written.
    */
   CBSTraceWriteCallback trace_write_callback;

   /**
    * Write buffer. Used as intermediate buffer when writing units.
    * For internal use of cbs only.
    */
   uint8_t *write_buffer;
   size_t   write_buffer_size;
} CodedBitstreamContext;


/**
* Table of all supported codec IDs.
*
* Terminated by AV_CODEC_ID_NONE.
*/
extern const enum AVCodecID ff_cbs_all_codec_ids[];


/**
* Create and initialise a new context for the given codec.
*/
int ff_cbs_init(CodedBitstreamContext **ctx,
               enum AVCodecID codec_id, void *log_ctx);

/**
* Reset all internal state in a context.
*/
void ff_cbs_flush(CodedBitstreamContext *ctx);

/**
* Close a context and free all internal state.
*/
void ff_cbs_close(CodedBitstreamContext **ctx);


/**
* Read the extradata bitstream found in codec parameters into a
* fragment, then split into units and decompose.
*
* This also updates the internal state, so will need to be called for
* codecs with extradata to read parameter sets necessary for further
* parsing even if the fragment itself is not desired.
*
* The fragment must have been zeroed or reset via ff_cbs_fragment_reset
* before use.
*/
int ff_cbs_read_extradata(CodedBitstreamContext *ctx,
                         CodedBitstreamFragment *frag,
                         const AVCodecParameters *par);

/**
* Read the extradata bitstream found in a codec context into a
* fragment, then split into units and decompose.
*
* This acts identical to ff_cbs_read_extradata() for the case where
* you already have a codec context.
*/
int ff_cbs_read_extradata_from_codec(CodedBitstreamContext *ctx,
                                    CodedBitstreamFragment *frag,
                                    const struct AVCodecContext *avctx);

int ff_cbs_read_packet_side_data(CodedBitstreamContext *ctx,
                                CodedBitstreamFragment *frag,
                                const AVPacket *pkt);

/**
* Read the data bitstream from a packet into a fragment, then
* split into units and decompose.
*
* This also updates the internal state of the coded bitstream context
* with any persistent data from the fragment which may be required to
* read following fragments (e.g. parameter sets).
*
* The fragment must have been zeroed or reset via ff_cbs_fragment_reset
* before use.
*/
int ff_cbs_read_packet(CodedBitstreamContext *ctx,
                      CodedBitstreamFragment *frag,
                      const AVPacket *pkt);

/**
* Read a bitstream from a memory region into a fragment, then
* split into units and decompose.
*
* This also updates the internal state of the coded bitstream context
* with any persistent data from the fragment which may be required to
* read following fragments (e.g. parameter sets).
*
* The fragment must have been zeroed or reset via ff_cbs_fragment_reset
* before use.
*/
int ff_cbs_read(CodedBitstreamContext *ctx,
               CodedBitstreamFragment *frag,
               const uint8_t *data, size_t size);


/**
* Write the content of the fragment to its own internal buffer.
*
* Writes the content of all units and then assembles them into a new
* data buffer.  When modifying the content of decomposed units, this
* can be used to regenerate the bitstream form of units or the whole
* fragment so that it can be extracted for other use.
*
* This also updates the internal state of the coded bitstream context
* with any persistent data from the fragment which may be required to
* write following fragments (e.g. parameter sets).
*/
int ff_cbs_write_fragment_data(CodedBitstreamContext *ctx,
                              CodedBitstreamFragment *frag);

/**
* Write the bitstream of a fragment to the extradata in codec parameters.
*
* Modifies context and fragment as ff_cbs_write_fragment_data does and
* replaces any existing extradata in the structure.
*/
int ff_cbs_write_extradata(CodedBitstreamContext *ctx,
                          AVCodecParameters *par,
                          CodedBitstreamFragment *frag);

/**
* Write the bitstream of a fragment to a packet.
*
* Modifies context and fragment as ff_cbs_write_fragment_data does.
*
* On success, the packet's buf is unreferenced and its buf, data and
* size fields are set to the corresponding values from the newly updated
* fragment; other fields are not touched.  On failure, the packet is not
* touched at all.
*/
int ff_cbs_write_packet(CodedBitstreamContext *ctx,
                       AVPacket *pkt,
                       CodedBitstreamFragment *frag);


/**
* Free the units contained in a fragment as well as the fragment's
* own data buffer, but not the units array itself.
*/
void ff_cbs_fragment_reset(CodedBitstreamFragment *frag);

/**
* Free the units array of a fragment in addition to what
* ff_cbs_fragment_reset does.
*/
void ff_cbs_fragment_free(CodedBitstreamFragment *frag);

/**
* Allocate a new internal content buffer matching the type of the unit.
*
* The content will be zeroed.
*/
int ff_cbs_alloc_unit_content(CodedBitstreamContext *ctx,
                             CodedBitstreamUnit *unit);

/**
* Insert a new unit into a fragment with the given content.
*
* If content_ref is supplied, it has to be a RefStruct reference
* backing content; the user keeps ownership of the supplied reference.
* The content structure continues to be owned by the caller if
* content_ref is not supplied.
*/
int ff_cbs_insert_unit_content(CodedBitstreamFragment *frag,
                              int position,
                              CodedBitstreamUnitType type,
                              void *content,
                              void *content_ref);

/**
* Add a new unit to a fragment with the given data bitstream.
*
* If data_buf is not supplied then data must have been allocated with
* av_malloc() and will on success become owned by the unit after this
* call or freed on error.
*/
int ff_cbs_append_unit_data(CodedBitstreamFragment *frag,
                           CodedBitstreamUnitType type,
                           uint8_t *data, size_t data_size,
                           AVBufferRef *data_buf);

/**
* Delete a unit from a fragment and free all memory it uses.
*
* Requires position to be >= 0 and < frag->nb_units.
*/
void ff_cbs_delete_unit(CodedBitstreamFragment *frag,
                       int position);


/**
* Make the content of a unit refcounted.
*
* If the unit is not refcounted, this will do a deep copy of the unit
* content to new refcounted buffers.
*
* It is not valid to call this function on a unit which does not have
* decomposed content.
*/
int ff_cbs_make_unit_refcounted(CodedBitstreamContext *ctx,
                               CodedBitstreamUnit *unit);

/**
* Make the content of a unit writable so that internal fields can be
* modified.
*
* If it is known that there are no other references to the content of
* the unit, does nothing and returns success.  Otherwise (including the
* case where the unit content is not refcounted), it does a full clone
* of the content (including any internal buffers) to make a new copy,
* and replaces the existing references inside the unit with that.
*
* It is not valid to call this function on a unit which does not have
* decomposed content.
*/
int ff_cbs_make_unit_writable(CodedBitstreamContext *ctx,
                             CodedBitstreamUnit *unit);

enum CbsDiscardFlags {
   DISCARD_FLAG_NONE = 0,

   /**
    * keep non-vcl units even if the picture has been dropped.
    */
   DISCARD_FLAG_KEEP_NON_VCL = 0x01,
};

/**
* Discard units accroding to 'skip'.
*/
void ff_cbs_discard_units(CodedBitstreamContext *ctx,
                         CodedBitstreamFragment *frag,
                         enum AVDiscard skip,
                         int flags);


/**
* Helper function for read tracing which formats the syntax element
* and logs the result.
*
* Trace context should be set to the CodedBitstreamContext.
*/
void ff_cbs_trace_read_log(void *trace_context,
                          struct GetBitContext *gbc, int length,
                          const char *str, const int *subscripts,
                          int64_t value);

/**
* Helper function for write tracing which formats the syntax element
* and logs the result.
*
* Trace context should be set to the CodedBitstreamContext.
*/
void ff_cbs_trace_write_log(void *trace_context,
                           struct PutBitContext *pbc, int length,
                           const char *str, const int *subscripts,
                           int64_t value);

#endif /* AVCODEC_CBS_H */