It's aspect ratio related, but why are some older Academy ratio films, cartoon shorts, and such sometimes presented in a window within a 4:3 picture (I'm not talking about pillarboxing to maintain the OAR on a 16:9 screen)?
I was most recently reminded about this when my local PBS station aired an episode of the Jack Benny Program the other day. While that one was 4:3 which is slightly different than the Academy film ratio, it was shown the same way with a border around the entire picture.
I am the farthest thing from an expert in terms of aspect ratio...but whenever I see something like this happen on broadcast television I always take it with a grain of salt because of all the variables involved along the chain that take the original source and deposit it in your home.
There is the source product>>the originating playback device>>the processing units which push the signal out their door>.the receipt of that signal at the cable company/dish company>>the processing of that signal by the satellite/dish company>.the way they send the signal (SD/HD, for example) over their system>>the settings on your cable box>>the way your cable box is wired to your display>>the settings on your display>>etc.
And there is any number of other variables that can work their way into the chain which can impact the way the original product appears on your set and result in it being stretched/squashed or even possibly correct.