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/libavformat/h261dec.c

http://github.com/FFmpeg/FFmpeg
C | 62 lines | 37 code | 5 blank | 20 comment | 11 complexity | 971033dae6c1aa61429dd7ee2abba326 MD5 | raw file
 1/*
 2 * RAW H.261 video demuxer
 3 * Copyright (c) 2009 Michael Niedermayer <michaelni@gmx.at>
 4 *
 5 * This file is part of FFmpeg.
 6 *
 7 * FFmpeg is free software; you can redistribute it and/or
 8 * modify it under the terms of the GNU Lesser General Public
 9 * License as published by the Free Software Foundation; either
10 * version 2.1 of the License, or (at your option) any later version.
11 *
12 * FFmpeg is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
15 * Lesser General Public License for more details.
16 *
17 * You should have received a copy of the GNU Lesser General Public
18 * License along with FFmpeg; if not, write to the Free Software
19 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
20 */
21
22#include "libavcodec/get_bits.h"
23#include "avformat.h"
24#include "rawdec.h"
25
26static int h261_probe(const AVProbeData *p)
27{
28    int i;
29    int valid_psc=0;
30    int invalid_psc=0;
31    int next_gn=0;
32    int src_fmt=0;
33
34    for(i=0; i<p->buf_size; i++){
35        if ((AV_RB16(&p->buf[i]) - 1) < 0xFFU) {
36            int shift = av_log2_16bit(p->buf[i+1]);
37            uint32_t code = AV_RB64(&p->buf[FFMAX(i-1, 0)]) >> (24+shift);
38            if ((code & 0xffff0000) == 0x10000) {
39                int gn= (code>>12)&0xf;
40                if(!gn)
41                    src_fmt= code&8;
42                if(gn != next_gn) invalid_psc++;
43                else              valid_psc++;
44
45                if(src_fmt){ // CIF
46                    static const int lut[16]={1,2,3,4,5,6,7,8,9,10,11,12,0,16,16,16};
47                    next_gn = lut[gn];
48                }else{       //QCIF
49                    static const int lut[16]={1,3,16,5,16,0,16,16,16,16,16,16,16,16,16,16};
50                    next_gn = lut[gn];
51                }
52            }
53        }
54    }
55    if(valid_psc > 2*invalid_psc + 6){
56        return AVPROBE_SCORE_EXTENSION;
57    }else if(valid_psc > 2*invalid_psc + 2)
58        return AVPROBE_SCORE_EXTENSION / 2;
59    return 0;
60}
61
62FF_DEF_RAWVIDEO_DEMUXER(h261, "raw H.261", h261_probe, "h261", AV_CODEC_ID_H261)