libavcodec/ac3_parser.c

   1 /*
   2  * AC3 parser
   3  * Copyright (c) 2003 Fabrice Bellard.
   4  * Copyright (c) 2003 Michael Niedermayer.
   5  *
   6  * This file is part of FFmpeg.
   7  *
   8  * FFmpeg is free software; you can redistribute it and/or
   9  * modify it under the terms of the GNU Lesser General Public
  10  * License as published by the Free Software Foundation; either
  11  * version 2.1 of the License, or (at your option) any later version.
  12  *
  13  * FFmpeg is distributed in the hope that it will be useful,
  14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  16  * Lesser General Public License for more details.
  17  *
  18  * You should have received a copy of the GNU Lesser General Public
  19  * License along with FFmpeg; if not, write to the Free Software
  20  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  21  */
  22
  23 #include "parser.h"
  24 #include "ac3_parser.h"
  25 #include "aac_ac3_parser.h"
  26 #include "bitstream.h"
  27
  28
  29 #define AC3_HEADER_SIZE 7
  30
  31
  32 static const uint8_t eac3_blocks[4] = {
  33     1, 2, 3, 6
  34 };
  35
  36
  37 int ff_ac3_parse_header(const uint8_t buf[7], AC3HeaderInfo *hdr)
  38 {
  39     GetBitContext gbc;
  40
  41     memset(hdr, 0, sizeof(*hdr));
  42
  43     init_get_bits(&gbc, buf, 54);
  44
  45     hdr->sync_word = get_bits(&gbc, 16);
  46     if(hdr->sync_word != 0x0B77)
  47         return -1;
  48
  49     /* read ahead to bsid to make sure this is AC-3, not E-AC-3 */
  50     hdr->bsid = show_bits_long(&gbc, 29) & 0x1F;
  51     if(hdr->bsid > 10)
  52         return -2;
  53
  54     hdr->crc1 = get_bits(&gbc, 16);
  55     hdr->fscod = get_bits(&gbc, 2);
  56     if(hdr->fscod == 3)
  57         return -3;
  58
  59     hdr->frmsizecod = get_bits(&gbc, 6);
  60     if(hdr->frmsizecod > 37)
  61         return -4;
  62
  63     skip_bits(&gbc, 5); // skip bsid, already got it
  64
  65     hdr->bsmod = get_bits(&gbc, 3);
  66     hdr->acmod = get_bits(&gbc, 3);
  67     if((hdr->acmod & 1) && hdr->acmod != 1) {
  68         hdr->cmixlev = get_bits(&gbc, 2);
  69     }
  70     if(hdr->acmod & 4) {
  71         hdr->surmixlev = get_bits(&gbc, 2);
  72     }
  73     if(hdr->acmod == 2) {
  74         hdr->dsurmod = get_bits(&gbc, 2);
  75     }
  76     hdr->lfeon = get_bits1(&gbc);
  77
  78     hdr->halfratecod = FFMAX(hdr->bsid, 8) - 8;
  79     hdr->sample_rate = ff_ac3_freqs[hdr->fscod] >> hdr->halfratecod;
  80     hdr->bit_rate = (ff_ac3_bitratetab[hdr->frmsizecod>>1] * 1000) >> hdr->halfratecod;
  81     hdr->channels = ff_ac3_channels[hdr->acmod] + hdr->lfeon;
  82     hdr->frame_size = ff_ac3_frame_sizes[hdr->frmsizecod][hdr->fscod] * 2;
  83
  84     return 0;
  85 }
  86
  87 static int ac3_sync(const uint8_t *buf, int *channels, int *sample_rate,
  88                     int *bit_rate, int *samples)
  89 {
  90     int err;
  91     unsigned int fscod, acmod, bsid, lfeon;
  92     unsigned int strmtyp, substreamid, frmsiz, fscod2, numblkscod;
  93     GetBitContext bits;
  94     AC3HeaderInfo hdr;
  95
  96     err = ff_ac3_parse_header(buf, &hdr);
  97
  98     if(err < 0 && err != -2)
  99         return 0;
 100
 101     bsid = hdr.bsid;
 102     if(bsid <= 10) {             /* Normal AC-3 */
 103         *sample_rate = hdr.sample_rate;
 104         *bit_rate = hdr.bit_rate;
 105         *channels = hdr.channels;
 106         *samples = AC3_FRAME_SIZE;
 107         return hdr.frame_size;
 108     } else if (bsid > 10 && bsid <= 16) { /* Enhanced AC-3 */
 109         init_get_bits(&bits, &buf[2], (AC3_HEADER_SIZE-2) * 8);
 110         strmtyp = get_bits(&bits, 2);
 111         substreamid = get_bits(&bits, 3);
 112
 113         if (strmtyp != 0 || substreamid != 0)
 114             return 0;   /* Currently don't support additional streams */
 115
 116         frmsiz = get_bits(&bits, 11) + 1;
 117         fscod = get_bits(&bits, 2);
 118         if (fscod == 3) {
 119             fscod2 = get_bits(&bits, 2);
 120             numblkscod = 3;
 121
 122             if(fscod2 == 3)
 123                 return 0;
 124
 125             *sample_rate = ff_ac3_freqs[fscod2] / 2;
 126         } else {
 127             numblkscod = get_bits(&bits, 2);
 128
 129             *sample_rate = ff_ac3_freqs[fscod];
 130         }
 131
 132         acmod = get_bits(&bits, 3);
 133         lfeon = get_bits1(&bits);
 134
 135         *samples = eac3_blocks[numblkscod] * 256;
 136         *bit_rate = frmsiz * (*sample_rate) * 16 / (*samples);
 137         *channels = ff_ac3_channels[acmod] + lfeon;
 138
 139         return frmsiz * 2;
 140     }
 141
 142     /* Unsupported bitstream version */
 143     return 0;
 144 }
 145
 146 static int ac3_parse_init(AVCodecParserContext *s1)
 147 {
 148     AACAC3ParseContext *s = s1->priv_data;
 149     s->inbuf_ptr = s->inbuf;
 150     s->header_size = AC3_HEADER_SIZE;
 151     s->sync = ac3_sync;
 152     return 0;
 153 }
 154
 155
 156 AVCodecParser ac3_parser = {
 157     { CODEC_ID_AC3 },
 158     sizeof(AACAC3ParseContext),
 159     ac3_parse_init,
 160     ff_aac_ac3_parse,
 161     NULL,
 162 };