libavcodec/mpegaudiodecheader.c

   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 }