If this is a personal recording from a smartphone or camera, it likely does not have DRM protection and can be opened with most modern media players: Use QuickTime Player or the Apple TV app.
If the file was purchased from iTunes and won't play on a non-Apple device, it is likely protected by FairPlay DRM, meaning it can only be viewed on authorized devices signed into your Apple ID.
If you are having trouble playing the video on certain devices (like a smart TV or an Android phone), you have a few easy options:
