FFmpeg: libavcodec/aacadtsdec.c Source File

00001 /*
00002  * Audio and Video frame extraction
00003  * Copyright (c) 2003 Fabrice Bellard
00004  * Copyright (c) 2003 Michael Niedermayer
00005  * Copyright (c) 2009 Alex Converse
00006  *
00007  * This file is part of FFmpeg.
00008  *
00009  * FFmpeg is free software; you can redistribute it and/or
00010  * modify it under the terms of the GNU Lesser General Public
00011  * License as published by the Free Software Foundation; either
00012  * version 2.1 of the License, or (at your option) any later version.
00013  *
00014  * FFmpeg is distributed in the hope that it will be useful,
00015  * but WITHOUT ANY WARRANTY; without even the implied warranty of
00016  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00017  * Lesser General Public License for more details.
00018  *
00019  * You should have received a copy of the GNU Lesser General Public
00020  * License along with FFmpeg; if not, write to the Free Software
00021  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
00022  */
00023 
00024 #include "aac_ac3_parser.h"
00025 #include "aacadtsdec.h"
00026 #include "get_bits.h"
00027 #include "mpeg4audio.h"
00028 
00029 int avpriv_aac_parse_header(GetBitContext *gbc, AACADTSHeaderInfo *hdr)
00030 {
00031     int size, rdb, ch, sr;
00032     int aot, crc_abs;
00033 
00034     if(get_bits(gbc, 12) != 0xfff)
00035         return AAC_AC3_PARSE_ERROR_SYNC;
00036 
00037     skip_bits1(gbc);             /* id */
00038     skip_bits(gbc, 2);           /* layer */
00039     crc_abs = get_bits1(gbc);    /* protection_absent */
00040     aot     = get_bits(gbc, 2);  /* profile_objecttype */
00041     sr      = get_bits(gbc, 4);  /* sample_frequency_index */
00042     if(!avpriv_mpeg4audio_sample_rates[sr])
00043         return AAC_AC3_PARSE_ERROR_SAMPLE_RATE;
00044     skip_bits1(gbc);             /* private_bit */
00045     ch      = get_bits(gbc, 3);  /* channel_configuration */
00046 
00047     skip_bits1(gbc);             /* original/copy */
00048     skip_bits1(gbc);             /* home */
00049 
00050     /* adts_variable_header */
00051     skip_bits1(gbc);             /* copyright_identification_bit */
00052     skip_bits1(gbc);             /* copyright_identification_start */
00053     size    = get_bits(gbc, 13); /* aac_frame_length */
00054     if(size < AAC_ADTS_HEADER_SIZE)
00055         return AAC_AC3_PARSE_ERROR_FRAME_SIZE;
00056 
00057     skip_bits(gbc, 11);          /* adts_buffer_fullness */
00058     rdb = get_bits(gbc, 2);      /* number_of_raw_data_blocks_in_frame */
00059 
00060     hdr->object_type    = aot + 1;
00061     hdr->chan_config    = ch;
00062     hdr->crc_absent     = crc_abs;
00063     hdr->num_aac_frames = rdb + 1;
00064     hdr->sampling_index = sr;
00065     hdr->sample_rate    = avpriv_mpeg4audio_sample_rates[sr];
00066     hdr->samples        = (rdb + 1) * 1024;
00067     hdr->bit_rate       = size * 8 * hdr->sample_rate / hdr->samples;
00068 
00069     return size;
00070 }