message: Allow to set av_log_set_level to reduce ffmpeg level below AV_LOG_ERROR
diff: @@ -850,6 +850,7 @@ static void ffmpeg_log_callback(void *ptr, int level, const char *fmt, va_list v
  static bool skip_header = false;
  static int prev_level = -1;
  CV_UNUSED(ptr);
  + if (level>av_log_get_level()) return;
  if (!skip_header || level != prev_level) printf("[OPENCV:FFMPEG:%02d] ", level);
  vprintf(fmt, vargs);
  size_t fmt_len = strlen(fmt);
  @@ -868,9 +869,15 @@ class InternalFFMpegRegister
  {
  #ifndef NO_GETENV
  char* debug_option = getenv("OPENCV_FFMPEG_DEBUG");
  - if (debug_option != NULL)
  + char* level_option = getenv("OPENCV_FFMPEG_LOGLEVEL");
  + int level = AV_LOG_VERBOSE;
  + if (level_option != NULL)
  {
  - av_log_set_level(AV_LOG_VERBOSE);
  + level = atoi(level_option);
  + }
  + if ( (debug_option != NULL) || (level_option != NULL) )
  + {
  + av_log_set_level(level);
  av_log_set_callback(ffmpeg_log_callback);
  }
  else
  