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  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 "avcodec.h"
  28. #include "mpegaudio.h"
  29. #include "mpegaudiodata.h"
  30. #include "mpegaudiodecheader.h"
  31.  
  32.  
  33. int avpriv_mpegaudio_decode_header(MPADecodeHeader *s, uint32_t header)
  34. {
  35.     int sample_rate, frame_size, mpeg25, padding;
  36.     int sample_rate_index, bitrate_index;
  37.     if (header & (1<<20)) {
  38.         s->lsf = (header & (1<<19)) ? 0 : 1;
  39.         mpeg25 = 0;
  40.     } else {
  41.         s->lsf = 1;
  42.         mpeg25 = 1;
  43.     }
  44.  
  45.     s->layer = 4 - ((header >> 17) & 3);
  46.     /* extract frequency */
  47.     sample_rate_index = (header >> 10) & 3;
  48.     sample_rate = avpriv_mpa_freq_tab[sample_rate_index] >> (s->lsf + mpeg25);
  49.     sample_rate_index += 3 * (s->lsf + mpeg25);
  50.     s->sample_rate_index = sample_rate_index;
  51.     s->error_protection = ((header >> 16) & 1) ^ 1;
  52.     s->sample_rate = sample_rate;
  53.  
  54.     bitrate_index = (header >> 12) & 0xf;
  55.     padding = (header >> 9) & 1;
  56.     //extension = (header >> 8) & 1;
  57.     s->mode = (header >> 6) & 3;
  58.     s->mode_ext = (header >> 4) & 3;
  59.     //copyright = (header >> 3) & 1;
  60.     //original = (header >> 2) & 1;
  61.     //emphasis = header & 3;
  62.  
  63.     if (s->mode == MPA_MONO)
  64.         s->nb_channels = 1;
  65.     else
  66.         s->nb_channels = 2;
  67.  
  68.     if (bitrate_index != 0) {
  69.         frame_size = avpriv_mpa_bitrate_tab[s->lsf][s->layer - 1][bitrate_index];
  70.         s->bit_rate = frame_size * 1000;
  71.         switch(s->layer) {
  72.         case 1:
  73.             frame_size = (frame_size * 12000) / sample_rate;
  74.             frame_size = (frame_size + padding) * 4;
  75.             break;
  76.         case 2:
  77.             frame_size = (frame_size * 144000) / sample_rate;
  78.             frame_size += padding;
  79.             break;
  80.         default:
  81.         case 3:
  82.             frame_size = (frame_size * 144000) / (sample_rate << s->lsf);
  83.             frame_size += padding;
  84.             break;
  85.         }
  86.         s->frame_size = frame_size;
  87.     } else {
  88.         /* if no frame size computed, signal it */
  89.         return 1;
  90.     }
  91.  
  92. #if defined(DEBUG)
  93.     av_dlog(NULL, "layer%d, %d Hz, %d kbits/s, ",
  94.            s->layer, s->sample_rate, s->bit_rate);
  95.     if (s->nb_channels == 2) {
  96.         if (s->layer == 3) {
  97.             if (s->mode_ext & MODE_EXT_MS_STEREO)
  98.                 av_dlog(NULL, "ms-");
  99.             if (s->mode_ext & MODE_EXT_I_STEREO)
  100.                 av_dlog(NULL, "i-");
  101.         }
  102.         av_dlog(NULL, "stereo");
  103.     } else {
  104.         av_dlog(NULL, "mono");
  105.     }
  106.     av_dlog(NULL, "\n");
  107. #endif
  108.     return 0;
  109. }
  110.  
  111. int avpriv_mpa_decode_header(AVCodecContext *avctx, uint32_t head, int *sample_rate, int *channels, int *frame_size, int *bit_rate)
  112. {
  113.     MPADecodeHeader s1, *s = &s1;
  114.  
  115.     if (ff_mpa_check_header(head) != 0)
  116.         return -1;
  117.  
  118.     if (avpriv_mpegaudio_decode_header(s, head) != 0) {
  119.         return -1;
  120.     }
  121.  
  122.     switch(s->layer) {
  123.     case 1:
  124.         avctx->codec_id = AV_CODEC_ID_MP1;
  125.         *frame_size = 384;
  126.         break;
  127.     case 2:
  128.         avctx->codec_id = AV_CODEC_ID_MP2;
  129.         *frame_size = 1152;
  130.         break;
  131.     default:
  132.     case 3:
  133.         avctx->codec_id = AV_CODEC_ID_MP3;
  134.         if (s->lsf)
  135.             *frame_size = 576;
  136.         else
  137.             *frame_size = 1152;
  138.         break;
  139.     }
  140.  
  141.     *sample_rate = s->sample_rate;
  142.     *channels = s->nb_channels;
  143.     *bit_rate = s->bit_rate;
  144.     return s->frame_size;
  145. }
  146.