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ffmpeg / libavformat / h261dec.c @ 2912e87a

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/*
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 * RAW H.261 video demuxer
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 * Copyright (c) 2009 Michael Niedermayer <michaelni@gmx.at>
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 *
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 * This file is part of Libav.
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 *
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 * Libav 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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 * Libav 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 Libav; 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 "libavcodec/get_bits.h"
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#include "avformat.h"
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#include "rawdec.h"
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static int h261_probe(AVProbeData *p)
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{
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    uint32_t code= -1;
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    int i;
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    int valid_psc=0;
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    int invalid_psc=0;
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    int next_gn=0;
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    int src_fmt=0;
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    GetBitContext gb;
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    init_get_bits(&gb, p->buf, p->buf_size*8);
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    for(i=0; i<p->buf_size*8; i++){
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        if ((code & 0x01ff0000) || !(code & 0xff00)) {
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            code = (code<<8) + get_bits(&gb, 8);
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            i += 7;
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        } else
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            code = (code<<1) + get_bits1(&gb);
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        if ((code & 0xffff0000) == 0x10000) {
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            int gn= (code>>12)&0xf;
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            if(!gn)
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                src_fmt= code&8;
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            if(gn != next_gn) invalid_psc++;
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            else              valid_psc++;
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            if(src_fmt){ // CIF
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                next_gn= (gn+1     )%13;
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            }else{       //QCIF
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                next_gn= (gn+1+!!gn)% 7;
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            }
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        }
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    }
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    if(valid_psc > 2*invalid_psc + 6){
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        return 50;
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    }else if(valid_psc > 2*invalid_psc + 2)
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        return 25;
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    return 0;
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}
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AVInputFormat ff_h261_demuxer = {
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    "h261",
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    NULL_IF_CONFIG_SMALL("raw H.261"),
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    0,
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    h261_probe,
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    ff_raw_video_read_header,
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    ff_raw_read_partial_packet,
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    .flags= AVFMT_GENERIC_INDEX,
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    .extensions = "h261",
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    .value = CODEC_ID_H261,
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};