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ffmpeg / libavcodec / ac3_parser.c @ 6808a8ea

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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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    int frame_size_code;
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    int num_blocks;
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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 AC3_PARSE_ERROR_SYNC;
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    /* read ahead to bsid to distinguish between AC-3 and E-AC-3 */
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    hdr->bitstream_id = show_bits_long(&gbc, 29) & 0x1F;
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    if(hdr->bitstream_id > 16)
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        return AC3_PARSE_ERROR_BSID;
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    if(hdr->bitstream_id <= 10) {
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        /* Normal AC-3 */
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        hdr->crc1 = get_bits(&gbc, 16);
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        hdr->sr_code = get_bits(&gbc, 2);
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        if(hdr->sr_code == 3)
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            return AC3_PARSE_ERROR_SAMPLE_RATE;
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        frame_size_code = get_bits(&gbc, 6);
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        if(frame_size_code > 37)
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            return AC3_PARSE_ERROR_FRAME_SIZE;
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        skip_bits(&gbc, 5); // skip bsid, already got it
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        skip_bits(&gbc, 3); // skip bitstream mode
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        hdr->channel_mode = get_bits(&gbc, 3);
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        if((hdr->channel_mode & 1) && hdr->channel_mode != AC3_CHMODE_MONO) {
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            skip_bits(&gbc, 2); // skip center mix level
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        }
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        if(hdr->channel_mode & 4) {
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            skip_bits(&gbc, 2); // skip surround mix level
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        }
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        if(hdr->channel_mode == AC3_CHMODE_STEREO) {
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            skip_bits(&gbc, 2); // skip dolby surround mode
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        }
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        hdr->lfe_on = get_bits1(&gbc);
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        hdr->sr_shift = FFMAX(hdr->bitstream_id, 8) - 8;
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        hdr->sample_rate = ff_ac3_sample_rate_tab[hdr->sr_code] >> hdr->sr_shift;
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        hdr->bit_rate = (ff_ac3_bitrate_tab[frame_size_code>>1] * 1000) >> hdr->sr_shift;
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        hdr->channels = ff_ac3_channels_tab[hdr->channel_mode] + hdr->lfe_on;
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        hdr->frame_size = ff_ac3_frame_size_tab[frame_size_code][hdr->sr_code] * 2;
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        hdr->stream_type = EAC3_STREAM_TYPE_INDEPENDENT;
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    } else {
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        /* Enhanced AC-3 */
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        hdr->crc1 = 0;
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        hdr->stream_type = get_bits(&gbc, 2);
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        if(hdr->stream_type == EAC3_STREAM_TYPE_RESERVED)
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            return AC3_PARSE_ERROR_STREAM_TYPE;
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        skip_bits(&gbc, 3); // skip substream id
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        hdr->frame_size = (get_bits(&gbc, 11) + 1) << 1;
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        if(hdr->frame_size < AC3_HEADER_SIZE)
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            return AC3_PARSE_ERROR_FRAME_SIZE;
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        hdr->sr_code = get_bits(&gbc, 2);
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        if (hdr->sr_code == 3) {
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            int sr_code2 = get_bits(&gbc, 2);
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            if(sr_code2 == 3)
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                return AC3_PARSE_ERROR_SAMPLE_RATE;
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            hdr->sample_rate = ff_ac3_sample_rate_tab[sr_code2] / 2;
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            hdr->sr_shift = 1;
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            num_blocks = 6;
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        } else {
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            num_blocks = eac3_blocks[get_bits(&gbc, 2)];
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            hdr->sample_rate = ff_ac3_sample_rate_tab[hdr->sr_code];
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            hdr->sr_shift = 0;
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        }
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        hdr->channel_mode = get_bits(&gbc, 3);
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        hdr->lfe_on = get_bits1(&gbc);
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        hdr->bit_rate = (uint32_t)(8.0 * hdr->frame_size * hdr->sample_rate /
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                        (num_blocks * 256.0));
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        hdr->channels = ff_ac3_channels_tab[hdr->channel_mode] + hdr->lfe_on;
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    }
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    return 0;
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}
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static int ac3_sync(AACAC3ParseContext *hdr_info)
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{
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    int err;
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    AC3HeaderInfo hdr;
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    err = ff_ac3_parse_header(hdr_info->inbuf, &hdr);
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    if(err < 0)
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        return 0;
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    hdr_info->sample_rate = hdr.sample_rate;
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    hdr_info->bit_rate = hdr.bit_rate;
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    hdr_info->channels = hdr.channels;
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    hdr_info->samples = AC3_FRAME_SIZE;
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    return hdr.frame_size;
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}
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static av_cold 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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};