Streaming Blu Ray to Apple TV
If I play a Blu Ray on my computer in iTunes could I Airplay it to an Apple TV?
Apple TV 4K
Question marked as
Hypothetically yes.
Playing a video on the computer screen and using AirPlay to 'mirror' it to an Apple TV is certainly possible.
Note: The sound quality over AirPlay will not support the much higher quality audio tracks possible on Blu-Ray discs so whilst you might get 5.1 support you will be unlikely to get lossless 5.1 e.g. Dolby Digital TruHD or DTS-HD support.
If rather than 'real' Blu-Ray discs you mean FullHD or even 4K movies purchased from the iTunes Store then these will definitely work via AirPlay but you could add your iTunes account directly to the AppleTV and have it play them directly from the iTunes Store without needing to AirPlay them from the computer. iTunes itself does not support playing from or importing from Blu-Ray discs.
Again hypothetically it would be possible to import (some) Blu-Ray discs via a separate tool in to iTunes, however in most countries this is considered illegal and we certainly cannot tell you how to do this here.