ac3_parser.c

/*
 * AC3 parser
 * Copyright (c) 2003 Fabrice Bellard.
 * Copyright (c) 2003 Michael Niedermayer.
 *
 * This file is part of FFmpeg.
 *
 * FFmpeg 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.
 *
 * FFmpeg 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 FFmpeg; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

#include "parser.h"
#include "ac3_parser.h"
#include "aac_ac3_parser.h"
#include "bitstream.h"


#define AC3_HEADER_SIZE 7


static const uint8_t eac3_blocks[4] = {
    1, 2, 3, 6
};


int ff_ac3_parse_header(const uint8_t buf[7], AC3HeaderInfo *hdr)
{
    GetBitContext gbc;

    memset(hdr, 0, sizeof(*hdr));

    init_get_bits(&gbc, buf, 54);

    hdr->sync_word = get_bits(&gbc, 16);
    if(hdr->sync_word != 0x0B77)
        return -1;

    /* read ahead to bsid to make sure this is AC-3, not E-AC-3 */
    hdr->bsid = show_bits_long(&gbc, 29) & 0x1F;
    if(hdr->bsid > 10)
        return -2;

    hdr->crc1 = get_bits(&gbc, 16);
    hdr->fscod = get_bits(&gbc, 2);
    if(hdr->fscod == 3)
        return -3;

    hdr->frmsizecod = get_bits(&gbc, 6);
    if(hdr->frmsizecod > 37)
        return -4;

    skip_bits(&gbc, 5); // skip bsid, already got it

    hdr->bsmod = get_bits(&gbc, 3);
    hdr->acmod = get_bits(&gbc, 3);
    if((hdr->acmod & 1) && hdr->acmod != AC3_ACMOD_MONO) {
        hdr->cmixlev = get_bits(&gbc, 2);
    }
    if(hdr->acmod & 4) {