do some MPEG-4 movies not work with Airplay?

Another add-on to my own post. I was very surprised to find that if I use my TV as a separate monitor, via System Settings on the Mac, I can play my mp4 sample movie (a paid-for documentary about the painter Vermeer) using QuickTime Player rather than via the Apple TV app!

As far as I know, the link between my Mac and my TV is using Airplay, so the warning given on the Apple TV app for this particular video - "This video is in a format that can't be streamed to this TV" - is incorrect.

This still doesn't help with showing certain movies which are only available via the TV app, even though I have paid for them thus theoretically avoiding any DRM issues.

It would be interesting to find out if I could play these movies using a different player, but as I said in my original post, they are hidden, and the locations don't show up on Spotlight. All very strange. I would like to hear from an expert on this.

Just to add to my own post, the main problem is that that type of error message doesn't contain enough information to allow one to make changes etc. Basically there ought to be a description of why a standard format like MPEG-4 doesn't always play. I suppose I must ask Apple Support.