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ffmpeg / libavcodec / ac3_parser.c @ 679c2294

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/*
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 * AC3 parser
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 * Copyright (c) 2003 Fabrice Bellard.
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 * Copyright (c) 2003 Michael Niedermayer.
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 *
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 * This file is part of FFmpeg.
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 *
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 * FFmpeg is free software; you can redistribute it and/or
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 * modify it under the terms of the GNU Lesser General Public
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 * License as published by the Free Software Foundation; either
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 * version 2.1 of the License, or (at your option) any later version.
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 *
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 * FFmpeg is distributed in the hope that it will be useful,
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 * but WITHOUT ANY WARRANTY; without even the implied warranty of
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 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
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 * Lesser General Public License for more details.
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 *
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 * You should have received a copy of the GNU Lesser General Public
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 * License along with FFmpeg; if not, write to the Free Software
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 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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 */
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#include "parser.h"
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#include "ac3_parser.h"
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#include "aac_ac3_parser.h"
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#include "bitstream.h"
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#define AC3_HEADER_SIZE 7
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static const uint8_t eac3_blocks[4] = {
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    1, 2, 3, 6
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};
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int ff_ac3_parse_header(const uint8_t buf[7], AC3HeaderInfo *hdr)
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{
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    GetBitContext gbc;
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    memset(hdr, 0, sizeof(*hdr));
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    init_get_bits(&gbc, buf, 54);
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    hdr->sync_word = get_bits(&gbc, 16);
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    if(hdr->sync_word != 0x0B77)
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        return -1;
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    /* read ahead to bsid to make sure this is AC-3, not E-AC-3 */
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    hdr->bsid = show_bits_long(&gbc, 29) & 0x1F;
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    if(hdr->bsid > 10)
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        return -2;
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    hdr->crc1 = get_bits(&gbc, 16);
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    hdr->fscod = get_bits(&gbc, 2);
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    if(hdr->fscod == 3)
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        return -3;
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    hdr->frmsizecod = get_bits(&gbc, 6);
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    if(hdr->frmsizecod > 37)
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        return -4;
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    skip_bits(&gbc, 5); // skip bsid, already got it
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    hdr->bsmod = get_bits(&gbc, 3);
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    hdr->acmod = get_bits(&gbc, 3);
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    if((hdr->acmod & 1) && hdr->acmod != 1) {
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        hdr->cmixlev = get_bits(&gbc, 2);
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    }
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    if(hdr->acmod & 4) {
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        hdr->surmixlev = get_bits(&gbc, 2);
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    }
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    if(hdr->acmod == 2) {
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        hdr->dsurmod = get_bits(&gbc, 2);
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    }
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    hdr->lfeon = get_bits1(&gbc);
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    hdr->halfratecod = FFMAX(hdr->bsid, 8) - 8;
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    hdr->sample_rate = ff_ac3_freqs[hdr->fscod] >> hdr->halfratecod;
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    hdr->bit_rate = (ff_ac3_bitratetab[hdr->frmsizecod>>1] * 1000) >> hdr->halfratecod;
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    hdr->channels = ff_ac3_channels[hdr->acmod] + hdr->lfeon;
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    hdr->frame_size = ff_ac3_frame_sizes[hdr->frmsizecod][hdr->fscod] * 2;
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    return 0;
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}
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static int ac3_sync(const uint8_t *buf, int *channels, int *sample_rate,
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                    int *bit_rate, int *samples)
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{
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    int err;
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    unsigned int fscod, acmod, bsid, lfeon;
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    unsigned int strmtyp, substreamid, frmsiz, fscod2, numblkscod;
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    GetBitContext bits;
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    AC3HeaderInfo hdr;
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    err = ff_ac3_parse_header(buf, &hdr);
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    if(err < 0 && err != -2)
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        return 0;
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    bsid = hdr.bsid;
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    if(bsid <= 10) {             /* Normal AC-3 */
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        *sample_rate = hdr.sample_rate;
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        *bit_rate = hdr.bit_rate;
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        *channels = hdr.channels;
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        *samples = AC3_FRAME_SIZE;
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        return hdr.frame_size;
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    } else if (bsid > 10 && bsid <= 16) { /* Enhanced AC-3 */
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        init_get_bits(&bits, &buf[2], (AC3_HEADER_SIZE-2) * 8);
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        strmtyp = get_bits(&bits, 2);
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        substreamid = get_bits(&bits, 3);
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        if (strmtyp != 0 || substreamid != 0)
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            return 0;   /* Currently don't support additional streams */
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        frmsiz = get_bits(&bits, 11) + 1;
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        fscod = get_bits(&bits, 2);
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        if (fscod == 3) {
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            fscod2 = get_bits(&bits, 2);
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            numblkscod = 3;
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            if(fscod2 == 3)
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                return 0;
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            *sample_rate = ff_ac3_freqs[fscod2] / 2;
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        } else {
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            numblkscod = get_bits(&bits, 2);
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            *sample_rate = ff_ac3_freqs[fscod];
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        }
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        acmod = get_bits(&bits, 3);
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        lfeon = get_bits1(&bits);
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        *samples = eac3_blocks[numblkscod] * 256;
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        *bit_rate = frmsiz * (*sample_rate) * 16 / (*samples);
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        *channels = ff_ac3_channels[acmod] + lfeon;
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        return frmsiz * 2;
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    }
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    /* Unsupported bitstream version */
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    return 0;
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}
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static int ac3_parse_init(AVCodecParserContext *s1)
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{
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    AACAC3ParseContext *s = s1->priv_data;
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    s->inbuf_ptr = s->inbuf;
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    s->header_size = AC3_HEADER_SIZE;
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    s->sync = ac3_sync;
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    return 0;
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}
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AVCodecParser ac3_parser = {
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    { CODEC_ID_AC3 },
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    sizeof(AACAC3ParseContext),
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    ac3_parse_init,
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    ff_aac_ac3_parse,
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    NULL,
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};