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libavformat/h261dec.c

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00001 /*
00002  * RAW H.261 video demuxer
00003  * Copyright (c) 2009 Michael Niedermayer <michaelni@gmx.at>
00004  *
00005  * This file is part of Libav.
00006  *
00007  * Libav is free software; you can redistribute it and/or
00008  * modify it under the terms of the GNU Lesser General Public
00009  * License as published by the Free Software Foundation; either
00010  * version 2.1 of the License, or (at your option) any later version.
00011  *
00012  * Libav is distributed in the hope that it will be useful,
00013  * but WITHOUT ANY WARRANTY; without even the implied warranty of
00014  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00015  * Lesser General Public License for more details.
00016  *
00017  * You should have received a copy of the GNU Lesser General Public
00018  * License along with Libav; if not, write to the Free Software
00019  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
00020  */
00021 
00022 #include "libavcodec/get_bits.h"
00023 #include "avformat.h"
00024 #include "rawdec.h"
00025 
00026 static int h261_probe(AVProbeData *p)
00027 {
00028     uint32_t code= -1;
00029     int i;
00030     int valid_psc=0;
00031     int invalid_psc=0;
00032     int next_gn=0;
00033     int src_fmt=0;
00034     GetBitContext gb;
00035 
00036     init_get_bits(&gb, p->buf, p->buf_size*8);
00037 
00038     for(i=0; i<p->buf_size*8; i++){
00039         if ((code & 0x01ff0000) || !(code & 0xff00)) {
00040             code = (code<<8) + get_bits(&gb, 8);
00041             i += 7;
00042         } else
00043             code = (code<<1) + get_bits1(&gb);
00044         if ((code & 0xffff0000) == 0x10000) {
00045             int gn= (code>>12)&0xf;
00046             if(!gn)
00047                 src_fmt= code&8;
00048             if(gn != next_gn) invalid_psc++;
00049             else              valid_psc++;
00050 
00051             if(src_fmt){ // CIF
00052                 next_gn= (gn+1     )%13;
00053             }else{       //QCIF
00054                 next_gn= (gn+1+!!gn)% 7;
00055             }
00056         }
00057     }
00058     if(valid_psc > 2*invalid_psc + 6){
00059         return 50;
00060     }else if(valid_psc > 2*invalid_psc + 2)
00061         return 25;
00062     return 0;
00063 }
00064 
00065 FF_DEF_RAWVIDEO_DEMUXER(h261, "raw H.261", h261_probe, "h261", CODEC_ID_H261)
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