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  1. /*
  2.  * Audio and Video frame extraction
  3.  * Copyright (c) 2003 Fabrice Bellard
  4.  * Copyright (c) 2003 Michael Niedermayer
  5.  * Copyright (c) 2009 Alex Converse
  6.  *
  7.  * This file is part of FFmpeg.
  8.  *
  9.  * FFmpeg is free software; you can redistribute it and/or
  10.  * modify it under the terms of the GNU Lesser General Public
  11.  * License as published by the Free Software Foundation; either
  12.  * version 2.1 of the License, or (at your option) any later version.
  13.  *
  14.  * FFmpeg is distributed in the hope that it will be useful,
  15.  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  16.  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  17.  * Lesser General Public License for more details.
  18.  *
  19.  * You should have received a copy of the GNU Lesser General Public
  20.  * License along with FFmpeg; if not, write to the Free Software
  21.  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  22.  */
  23.  
  24. #include "aac_ac3_parser.h"
  25. #include "aacadtsdec.h"
  26. #include "get_bits.h"
  27. #include "mpeg4audio.h"
  28.  
  29. int avpriv_aac_parse_header(GetBitContext *gbc, AACADTSHeaderInfo *hdr)
  30. {
  31.     int size, rdb, ch, sr;
  32.     int aot, crc_abs;
  33.  
  34.     if(get_bits(gbc, 12) != 0xfff)
  35.         return AAC_AC3_PARSE_ERROR_SYNC;
  36.  
  37.     skip_bits1(gbc);             /* id */
  38.     skip_bits(gbc, 2);           /* layer */
  39.     crc_abs = get_bits1(gbc);    /* protection_absent */
  40.     aot     = get_bits(gbc, 2);  /* profile_objecttype */
  41.     sr      = get_bits(gbc, 4);  /* sample_frequency_index */
  42.     if(!avpriv_mpeg4audio_sample_rates[sr])
  43.         return AAC_AC3_PARSE_ERROR_SAMPLE_RATE;
  44.     skip_bits1(gbc);             /* private_bit */
  45.     ch      = get_bits(gbc, 3);  /* channel_configuration */
  46.  
  47.     skip_bits1(gbc);             /* original/copy */
  48.     skip_bits1(gbc);             /* home */
  49.  
  50.     /* adts_variable_header */
  51.     skip_bits1(gbc);             /* copyright_identification_bit */
  52.     skip_bits1(gbc);             /* copyright_identification_start */
  53.     size    = get_bits(gbc, 13); /* aac_frame_length */
  54.     if(size < AAC_ADTS_HEADER_SIZE)
  55.         return AAC_AC3_PARSE_ERROR_FRAME_SIZE;
  56.  
  57.     skip_bits(gbc, 11);          /* adts_buffer_fullness */
  58.     rdb = get_bits(gbc, 2);      /* number_of_raw_data_blocks_in_frame */
  59.  
  60.     hdr->object_type    = aot + 1;
  61.     hdr->chan_config    = ch;
  62.     hdr->crc_absent     = crc_abs;
  63.     hdr->num_aac_frames = rdb + 1;
  64.     hdr->sampling_index = sr;
  65.     hdr->sample_rate    = avpriv_mpeg4audio_sample_rates[sr];
  66.     hdr->samples        = (rdb + 1) * 1024;
  67.     hdr->bit_rate       = size * 8 * hdr->sample_rate / hdr->samples;
  68.  
  69.     return size;
  70. }
  71.