FFmpeg/libavformat/ac3dec.c

/*
 * RAW AC-3 and E-AC-3 demuxer
 * Copyright (c) 2007 Justin Ruggles <justin.ruggles@gmail.com>
 *
 * This file is part of Libav.
 *
 * Libav is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * Libav is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with Libav; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

#include "libavutil/crc.h"
#include "libavcodec/ac3_parser.h"
#include "avformat.h"
#include "rawdec.h"

static int ac3_eac3_probe(AVProbeData *p, enum CodecID expected_codec_id)
{
    int max_frames, first_frames = 0, frames;
    uint8_t *buf, *buf2, *end;
    AC3HeaderInfo hdr;
    GetBitContext gbc;
    enum CodecID codec_id = CODEC_ID_AC3;

    max_frames = 0;
    buf = p->buf;
    end = buf + p->buf_size;

    for(; buf < end; buf++) {
        buf2 = buf;

        for(frames = 0; buf2 < end; frames++) {
            init_get_bits(&gbc, buf2, 54);
            if(ff_ac3_parse_header(&gbc, &hdr) < 0)
                break;
            if(buf2 + hdr.frame_size > end ||
               av_crc(av_crc_get_table(AV_CRC_16_ANSI), 0, buf2 + 2, hdr.frame_size - 2))
                break;
            if (hdr.bitstream_id > 10)
                codec_id = CODEC_ID_EAC3;
            buf2 += hdr.frame_size;
        }
        max_frames = FFMAX(max_frames, frames);
        if(buf == p->buf)
            first_frames = frames;
    }
    if(codec_id != expected_codec_id) return 0;
    // keep this in sync with mp3 probe, both need to avoid
    // issues with MPEG-files!
    if   (first_frames>=4) return AVPROBE_SCORE_MAX/2+1;
    else if(max_frames>500)return AVPROBE_SCORE_MAX/2;
    else if(max_frames>=4) return AVPROBE_SCORE_MAX/4;
    else if(max_frames>=1) return 1;
    else                   return 0;
}

#if CONFIG_AC3_DEMUXER
static int ac3_probe(AVProbeData *p)
{
    return ac3_eac3_probe(p, CODEC_ID_AC3);
}

AVInputFormat ff_ac3_demuxer = {
    "ac3",
    NULL_IF_CONFIG_SMALL("raw AC-3"),
    0,
    ac3_probe,
    ff_raw_audio_read_header,
    ff_raw_read_partial_packet,
    .flags= AVFMT_GENERIC_INDEX,
    .extensions = "ac3",
    .value = CODEC_ID_AC3,
};
#endif

#if CONFIG_EAC3_DEMUXER
static int eac3_probe(AVProbeData *p)
{
    return ac3_eac3_probe(p, CODEC_ID_EAC3);
}

AVInputFormat ff_eac3_demuxer = {
    "eac3",
    NULL_IF_CONFIG_SMALL("raw E-AC-3"),
    0,
    eac3_probe,
    ff_raw_audio_read_header,
    ff_raw_read_partial_packet,
    .flags= AVFMT_GENERIC_INDEX,
    .extensions = "eac3",
    .value = CODEC_ID_EAC3,
};
#endif