message: try to fix VideoCapture different time stamp
diff: @@ -496,7 +496,7 @@ struct CvCapture_FFMPEG
  double r2d(AVRational r) const;
  int64_t dts_to_frame_number(int64_t dts);
  - double dts_to_sec(int64_t dts);
  + double dts_to_sec(int64_t dts) const;
  AVFormatContext * ic;
  AVCodec * avcodec;
  @@ -1167,7 +1167,11 @@ double CvCapture_FFMPEG::getProperty( int property_id ) const
  switch( property_id )
  {
  case CV_FFMPEG_CAP_PROP_POS_MSEC:
  - return 1000.0*(double)frame_number/get_fps();
  + if (picture_pts == AV_NOPTS_VALUE_)
  + {
  + return 0;
  + }
  + return (dts_to_sec(picture_pts) * 1000);
  case CV_FFMPEG_CAP_PROP_POS_FRAMES:
  return (double)frame_number;
  case CV_FFMPEG_CAP_PROP_POS_AVI_RATIO:
  @@ -1277,7 +1281,7 @@ int64_t CvCapture_FFMPEG::dts_to_frame_number(int64_t dts)
  return (int64_t)(get_fps() * sec + 0.5);
  }
  -double CvCapture_FFMPEG::dts_to_sec(int64_t dts)
  +double CvCapture_FFMPEG::dts_to_sec(int64_t dts) const
  {
  return (double)(dts - ic->streams[video_stream]->start_time) *
  r2d(ic->streams[video_stream]->time_base);
  