tor-browser

The Tor Browser
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mpegaudiodecheader.c (4313B)

      1 /*
      2 * MPEG Audio header decoder
      3 * Copyright (c) 2001, 2002 Fabrice Bellard
      4 *
      5 * This file is part of FFmpeg.
      6 *
      7 * FFmpeg is free software; you can redistribute it and/or
      8 * modify it under the terms of the GNU Lesser General Public
      9 * License as published by the Free Software Foundation; either
     10 * version 2.1 of the License, or (at your option) any later version.
     11 *
     12 * FFmpeg is distributed in the hope that it will be useful,
     13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
     14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
     15 * Lesser General Public License for more details.
     16 *
     17 * You should have received a copy of the GNU Lesser General Public
     18 * License along with FFmpeg; if not, write to the Free Software
     19 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
     20 */
     21 
     22 /**
     23 * @file
     24 * MPEG Audio header decoder.
     25 */
     26 
     27 #include "libavutil/macros.h"
     28 
     29 #include "mpegaudio.h"
     30 #include "mpegaudiodata.h"
     31 #include "mpegaudiodecheader.h"
     32 
     33 
     34 int avpriv_mpegaudio_decode_header(MPADecodeHeader *s, uint32_t header)
     35 {
     36    int sample_rate, frame_size, mpeg25, padding;
     37    int sample_rate_index, bitrate_index;
     38    int ret;
     39 
     40    ret = ff_mpa_check_header(header);
     41    if (ret < 0)
     42        return ret;
     43 
     44    if (header & (1<<20)) {
     45        s->lsf = (header & (1<<19)) ? 0 : 1;
     46        mpeg25 = 0;
     47    } else {
     48        s->lsf = 1;
     49        mpeg25 = 1;
     50    }
     51 
     52    s->layer = 4 - ((header >> 17) & 3);
     53    /* extract frequency */
     54    sample_rate_index = (header >> 10) & 3;
     55    if (sample_rate_index >= FF_ARRAY_ELEMS(ff_mpa_freq_tab))
     56        sample_rate_index = 0;
     57    sample_rate = ff_mpa_freq_tab[sample_rate_index] >> (s->lsf + mpeg25);
     58    sample_rate_index += 3 * (s->lsf + mpeg25);
     59    s->sample_rate_index = sample_rate_index;
     60    s->error_protection = ((header >> 16) & 1) ^ 1;
     61    s->sample_rate = sample_rate;
     62 
     63    bitrate_index = (header >> 12) & 0xf;
     64    padding = (header >> 9) & 1;
     65    //extension = (header >> 8) & 1;
     66    s->mode = (header >> 6) & 3;
     67    s->mode_ext = (header >> 4) & 3;
     68    //copyright = (header >> 3) & 1;
     69    //original = (header >> 2) & 1;
     70    //emphasis = header & 3;
     71 
     72    if (s->mode == MPA_MONO)
     73        s->nb_channels = 1;
     74    else
     75        s->nb_channels = 2;
     76 
     77    if (bitrate_index != 0) {
     78        frame_size = ff_mpa_bitrate_tab[s->lsf][s->layer - 1][bitrate_index];
     79        s->bit_rate = frame_size * 1000;
     80        switch(s->layer) {
     81        case 1:
     82            frame_size = (frame_size * 12000) / sample_rate;
     83            frame_size = (frame_size + padding) * 4;
     84            break;
     85        case 2:
     86            frame_size = (frame_size * 144000) / sample_rate;
     87            frame_size += padding;
     88            break;
     89        default:
     90        case 3:
     91            frame_size = (frame_size * 144000) / (sample_rate << s->lsf);
     92            frame_size += padding;
     93            break;
     94        }
     95        s->frame_size = frame_size;
     96    } else {
     97        /* if no frame size computed, signal it */
     98        return 1;
     99    }
    100 
    101 #if defined(DEBUG)
    102    ff_dlog(NULL, "layer%d, %d Hz, %d kbits/s, ",
    103           s->layer, s->sample_rate, s->bit_rate);
    104    if (s->nb_channels == 2) {
    105        if (s->layer == 3) {
    106            if (s->mode_ext & MODE_EXT_MS_STEREO)
    107                ff_dlog(NULL, "ms-");
    108            if (s->mode_ext & MODE_EXT_I_STEREO)
    109                ff_dlog(NULL, "i-");
    110        }
    111        ff_dlog(NULL, "stereo");
    112    } else {
    113        ff_dlog(NULL, "mono");
    114    }
    115    ff_dlog(NULL, "\n");
    116 #endif
    117    return 0;
    118 }
    119 
    120 int ff_mpa_decode_header(uint32_t head, int *sample_rate, int *channels, int *frame_size, int *bit_rate, enum AVCodecID *codec_id)
    121 {
    122    MPADecodeHeader s1, *s = &s1;
    123 
    124    if (avpriv_mpegaudio_decode_header(s, head) != 0) {
    125        return -1;
    126    }
    127 
    128    switch(s->layer) {
    129    case 1:
    130        *codec_id = AV_CODEC_ID_MP1;
    131        *frame_size = 384;
    132        break;
    133    case 2:
    134        *codec_id = AV_CODEC_ID_MP2;
    135        *frame_size = 1152;
    136        break;
    137    default:
    138    case 3:
    139        if (*codec_id != AV_CODEC_ID_MP3ADU)
    140            *codec_id = AV_CODEC_ID_MP3;
    141        if (s->lsf)
    142            *frame_size = 576;
    143        else
    144            *frame_size = 1152;
    145        break;
    146    }
    147 
    148    *sample_rate = s->sample_rate;
    149    *channels = s->nb_channels;
    150    *bit_rate = s->bit_rate;
    151    return s->frame_size;
    152 }