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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_bits8(&gb, p->buf, p->buf_size);
  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 AVPROBE_SCORE_EXTENSION;
  60.     }else if(valid_psc > 2*invalid_psc + 2)
  61.         return AVPROBE_SCORE_EXTENSION / 2;
  62.     return 0;
  63. }
  64.  
  65. FF_DEF_RAWVIDEO_DEMUXER(h261, "raw H.261", h261_probe, "h261", AV_CODEC_ID_H261)
  66.