message: Fixes 11480 : allow to force the video codec used to read videos
  with the ffmpeg backend
diff: @@ -870,7 +870,12 @@ bool CvCapture_FFMPEG::open( const char* _filename )
  int enc_width = enc->width;
  int enc_height = enc->height;
  - AVCodec *codec = avcodec_find_decoder(enc->codec_id);
  + AVCodec *codec;
  + if(av_dict_get(dict, "video_codec", NULL, 0) == NULL) {
  + codec = avcodec_find_decoder(enc->codec_id);
  + } else {
  + codec = avcodec_find_decoder_by_name(av_dict_get(dict, "video_codec", NULL, 0)->value);
  + }
  if (!codec ||
  #if LIBAVCODEC_VERSION_INT >= ((53<<16)+(8<<8)+0)
  avcodec_open2(enc, codec, NULL)
  