libavformat/ac3dec.c

   1 /*
   2  * RAW AC-3 and E-AC-3 demuxer
   3  * Copyright (c) 2007 Justin Ruggles <justin.ruggles@gmail.com>
   4  *
   5  * This file is part of Libav.
   6  *
   7  * Libav 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  * Libav 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 Libav; if not, write to the Free Software
  19  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  20  */
  21
  22 #include "libavutil/crc.h"
  23 #include "libavcodec/ac3_parser.h"
  24 #include "avformat.h"
  25 #include "rawdec.h"
  26
  27 static int ac3_eac3_probe(AVProbeData *p, enum AVCodecID expected_codec_id)
  28 {
  29     int max_frames, first_frames = 0, frames;
  30     uint8_t *buf, *buf2, *end;
  31     AC3HeaderInfo hdr;
  32     GetBitContext gbc;
  33     enum AVCodecID codec_id = AV_CODEC_ID_AC3;
  34
  35     max_frames = 0;
  36     buf = p->buf;
  37     end = buf + p->buf_size;
  38
  39     for(; buf < end; buf++) {
  40         buf2 = buf;
  41
  42         for(frames = 0; buf2 < end; frames++) {
  43             init_get_bits(&gbc, buf2, 54);
  44             if(avpriv_ac3_parse_header(&gbc, &hdr) < 0)
  45                 break;
  46             if(buf2 + hdr.frame_size > end ||
  47                av_crc(av_crc_get_table(AV_CRC_16_ANSI), 0, buf2 + 2, hdr.frame_size - 2))
  48                 break;
  49             if (hdr.bitstream_id > 10)
  50                 codec_id = AV_CODEC_ID_EAC3;
  51             buf2 += hdr.frame_size;
  52         }
  53         max_frames = FFMAX(max_frames, frames);
  54         if(buf == p->buf)
  55             first_frames = frames;
  56     }
  57     if(codec_id != expected_codec_id) return 0;
  58     // keep this in sync with mp3 probe, both need to avoid
  59     // issues with MPEG-files!
  60     if (first_frames >= 4) return AVPROBE_SCORE_MAX / 2 + 1;
  61
  62     if (max_frames) {
  63         int pes = 0, i;
  64         unsigned int code = -1;
  65
  66 #define VIDEO_ID 0x000001e0
  67 #define AUDIO_ID 0x000001c0
  68         /* do a search for mpegps headers to be able to properly bias
  69          * towards mpegps if we detect this stream as both. */
  70         for (i = 0; i<p->buf_size; i++) {
  71             code = (code << 8) + p->buf[i];
  72             if ((code & 0xffffff00) == 0x100) {
  73                 if     ((code & 0x1f0) == VIDEO_ID) pes++;
  74                 else if((code & 0x1e0) == AUDIO_ID) pes++;
  75             }
  76         }
  77
  78         if (pes)
  79             max_frames = (max_frames + pes - 1) / pes;
  80     }
  81     if      (max_frames >  500) return AVPROBE_SCORE_MAX / 2;
  82     else if (max_frames >= 4)   return AVPROBE_SCORE_MAX / 4;
  83     else if (max_frames >= 1)   return 1;
  84     else                        return 0;
  85 }
  86
  87 #if CONFIG_AC3_DEMUXER
  88 static int ac3_probe(AVProbeData *p)
  89 {
  90     return ac3_eac3_probe(p, AV_CODEC_ID_AC3);
  91 }
  92
  93 AVInputFormat ff_ac3_demuxer = {
  94     .name           = "ac3",
  95     .long_name      = NULL_IF_CONFIG_SMALL("raw AC-3"),
  96     .read_probe     = ac3_probe,
  97     .read_header    = ff_raw_audio_read_header,
  98     .read_packet    = ff_raw_read_partial_packet,
  99     .flags= AVFMT_GENERIC_INDEX,
 100     .extensions = "ac3",
 101     .raw_codec_id   = AV_CODEC_ID_AC3,
 102 };
 103 #endif
 104
 105 #if CONFIG_EAC3_DEMUXER
 106 static int eac3_probe(AVProbeData *p)
 107 {
 108     return ac3_eac3_probe(p, AV_CODEC_ID_EAC3);
 109 }
 110
 111 AVInputFormat ff_eac3_demuxer = {
 112     .name           = "eac3",
 113     .long_name      = NULL_IF_CONFIG_SMALL("raw E-AC-3"),
 114     .read_probe     = eac3_probe,
 115     .read_header    = ff_raw_audio_read_header,
 116     .read_packet    = ff_raw_read_partial_packet,
 117     .flags          = AVFMT_GENERIC_INDEX,
 118     .extensions     = "eac3",
 119     .raw_codec_id   = AV_CODEC_ID_EAC3,
 120 };
 121 #endif