libavformat/h261dec.c

   1 /*
   2  * RAW H.261 video demuxer
   3  * Copyright (c) 2009 Michael Niedermayer <michaelni@gmx.at>
   4  *
   5  * This file is part of Libav.
   6  *
   7  * Libav 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  * Libav 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 Libav; 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)