libavcodec/mpeg4audio.c

   1 /*
   2  * MPEG-4 Audio common code
   3  * Copyright (c) 2008 Baptiste Coudurier <baptiste.coudurier@free.fr>
   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 #include "bitstream.h"
  23 #include "mpeg4audio.h"
  24
  25 const int ff_mpeg4audio_sample_rates[16] = {
  26     96000, 88200, 64000, 48000, 44100, 32000,
  27     24000, 22050, 16000, 12000, 11025, 8000, 7350
  28 };
  29
  30 const uint8_t ff_mpeg4audio_channels[8] = {
  31     0, 1, 2, 3, 4, 5, 6, 8
  32 };
  33
  34 static inline int get_object_type(GetBitContext *gb)
  35 {
  36     int object_type = get_bits(gb, 5);
  37     if (object_type == 31)
  38         object_type = 32 + get_bits(gb, 6);
  39     return object_type;
  40 }
  41
  42 static inline int get_sample_rate(GetBitContext *gb, int *index)
  43 {
  44     *index = get_bits(gb, 4);
  45     return *index == 0x0f ? get_bits(gb, 24) :
  46         ff_mpeg4audio_sample_rates[*index];
  47 }
  48
  49 int ff_mpeg4audio_get_config(MPEG4AudioConfig *c, const uint8_t *buf, int buf_size)
  50 {
  51     GetBitContext gb;
  52     int specific_config_bitindex;
  53
  54     init_get_bits(&gb, buf, buf_size*8);
  55     c->object_type = get_object_type(&gb);
  56     c->sample_rate = get_sample_rate(&gb, &c->sampling_index);
  57     c->chan_config = get_bits(&gb, 4);
  58     c->sbr = -1;
  59     if (c->object_type == 5) {
  60         c->ext_object_type = c->object_type;
  61         c->sbr = 1;
  62         c->ext_sample_rate = get_sample_rate(&gb, &c->ext_sampling_index);
  63         c->object_type = get_object_type(&gb);
  64     } else
  65         c->ext_object_type = 0;
  66
  67     specific_config_bitindex = get_bits_count(&gb);
  68
  69     if (c->ext_object_type != 5) {
  70         int bits_left = buf_size*8 - specific_config_bitindex;
  71         for (; bits_left > 15; bits_left--) {
  72             if (show_bits(&gb, 11) == 0x2b7) { // sync extension
  73                 get_bits(&gb, 11);
  74                 c->ext_object_type = get_object_type(&gb);
  75                 if (c->ext_object_type == 5 && (c->sbr = get_bits1(&gb)) == 1)
  76                     c->ext_sample_rate = get_sample_rate(&gb, &c->ext_sampling_index);
  77                 break;
  78             } else
  79                 get_bits1(&gb); // skip 1 bit
  80         }
  81     }
  82     return specific_config_bitindex;
  83 }