see https://forums.plex.tv/discussion/302396/movies-playing-with-large-black-box
white = the original movie picture in 16:9 aspect ratio
black = the letterboxing added to the picture on the original DVD, which forms a 4:3 tv frame
grey = the border which results in Plex attempting to show you the full “4:3” video on a 16:9 screen (which in fact is not a 4:3 video but Plex cannot know that since the video stream has technically a 4:3 aspect ratio)
