message: print a debug message if the environment variables OPENCV_FFMPEG_CAPTURE_OPTIONS and OPENCV_FFMPEG_WRITER_OPTIONS are set
diff: @@ -1116,6 +1116,7 @@ bool CvCapture_FFMPEG::open(const char* _filename, const VideoCaptureParameters&
  }
  else
  {
  + CV_LOG_DEBUG(NULL, "VIDEOIO/FFMPEG: using capture options from environment: " << options);
  #if LIBAVUTIL_BUILD >= (LIBAVUTIL_VERSION_MICRO >= 100 ? CALC_FFMPEG_VERSION(52, 17, 100) : CALC_FFMPEG_VERSION(52, 7, 0))
  av_dict_parse_string(&dict, options, ";", "|", 0);
  #else
  @@ -2911,7 +2912,9 @@ bool CvVideoWriter_FFMPEG::open( const char * filename, int fourcc,
  AVDictionary *dict = NULL;
  #if !defined(NO_GETENV) && (LIBAVUTIL_VERSION_MAJOR >= 53)
  char* options = getenv("OPENCV_FFMPEG_WRITER_OPTIONS");
  - if (options) {
  + if (options)
  + {
  + CV_LOG_DEBUG(NULL, "VIDEOIO/FFMPEG: using writer options from environment: " << options);
  av_dict_parse_string(&dict, options, ";", "|", 0);
  }
  #endif
  