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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.     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.  
  62. FF_DEF_RAWVIDEO_DEMUXER(h261, "raw H.261", h261_probe, "h261", AV_CODEC_ID_H261)
  63.