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h261dec.c
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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 
26 static int h261_probe(AVProbeData *p)
27 {
28  uint32_t code= -1;
29  int i;
30  int valid_psc=0;
31  int invalid_psc=0;
32  int next_gn=0;
33  int src_fmt=0;
34  GetBitContext gb;
35 
36  init_get_bits(&gb, p->buf, p->buf_size*8);
37 
38  for(i=0; i<p->buf_size*8; i++){
39  if ((code & 0x01ff0000) || !(code & 0xff00)) {
40  code = (code<<8) + get_bits(&gb, 8);
41  i += 7;
42  } else
43  code = (code<<1) + get_bits1(&gb);
44  if ((code & 0xffff0000) == 0x10000) {
45  int gn= (code>>12)&0xf;
46  if(!gn)
47  src_fmt= code&8;
48  if(gn != next_gn) invalid_psc++;
49  else valid_psc++;
50 
51  if(src_fmt){ // CIF
52  next_gn= (gn+1 )%13;
53  }else{ //QCIF
54  next_gn= (gn+1+!!gn)% 7;
55  }
56  }
57  }
58  if(valid_psc > 2*invalid_psc + 6){
59  return 50;
60  }else if(valid_psc > 2*invalid_psc + 2)
61  return 25;
62  return 0;
63 }
64 
65 FF_DEF_RAWVIDEO_DEMUXER(h261, "raw H.261", h261_probe, "h261", AV_CODEC_ID_H261)