Set the movie format for Pages documents on iPad
By default, Pages converts HEVC movies to H.264 so they can be viewed on older Macs and older iOS devices. You can change this setting if you want to use movies that were formatted using High Efficiency Video Encoding (HEVC).
Allow HEVC movies
Tap , then tap Settings.
Tap Adding Movies, then turn off Optimize for Older Devices.
With this setting turned off, you can add HEVC movies to your document and they retain their formatting. This setting applies only to movies you add from now on and not to any existing movies in your documents.
Note: iOS versions earlier than iOS 13 don’t support transparency in HEVC movies, so if your HEVC movie has transparency (for example, in the background), whatever is encoded in the movie (for example, black) is shown instead.