Apple apps such as TV and Quicktime won't stream home videos

I’ve tested AirPlay streaming to an Apple TV 4K box with tvOS 14.4, with an iMac with macOS 10.12.6, a MacBook Pro with macOS 11.2.3, an iPhone 12 Mini with iOS 14.4.1, and an iPad Air with iPadOS 14.4.1, and several earlier OS versions in the past.

I’ve used the above test file yesterday and at various times previously, as well as other clips with various properties (and variations) from my folder with test clips.

I’ve tested with the TV app, QuickTime Player, Safari, even the iTunes application [basic AirPlay] and other media players [Mac screen mirroring], and also clips in the Photos app (iOS/iPadOS) (recorded and/or where they end up through AirDrop).

It seems one can’t load Home Sharing content on an iOS device and then AirPlay that to a TV. It seems it has to be direct from source to destination. Otherwise I would get the mentioned format error as well.

Unfortunately, I can’t replicate your issue with my setup. AirPlay works fine for my files and devices. Hard to tell what you do differently, going by your description.

Please review these documents for clues.

Use AirPlay to stream video or mirror your device’s screen - Apple Support

If AirPlay or screen mirroring isn’t working on your device - Apple Support

If the issue is specific to files that you tried, then there should be other files that work fine.

Try AirPlaying this file: https://we.tl/t-tKoZx7wpUe

Does it also error on screen mirroring the Mac desktop or iPhone home screen?

At this time, I would suggest that you contact an expert from the Apple Support staff for further assistance. Possibly they know of things to check or change that I haven’t thought of.