Few seconds of a low quality TV video into a low quality YouTube film is a huge challenge. I'm sort of known for being good at deep Web digging, but after 2 hours of searching I had to desist.
What we know so far is:
- The Apartment is a film from 1960, so we have to search for a film shot before that year.
- In the few seconds insert, a 7th Cavalry's flag is noticeable (see: https://www.google.com/search?q=7th+Cav ... 00&bih=804). The same 7th Cavarly Regiment notorious for the Indian Wars (won and lost), and for General Custer. Almost watched all recordings available in Internet of "Cavalry Western films" without being able to catch the scene.
What we could presume, but are not sure of:
- From the frames you can see, it's unlikely that it could be a TV series (like The Adventures of Rin Tin Tin, for example). It should definitely be a movie.
is a black and white movie, but since first color movies date way back (first experiments, 1903), and color TV was introduced in the U.S. in 1953/1954, there's no reason to presume that the frames are taken from a B/W movie.
I'd suggest you to ask in a more Western-movies-centered forum (there are some very well informed around here, though I'm not able to give you any good direction, at the moment).
May I ask you why you're so interested in this detail?