To share a movie or a TV show together, click on the iPad with a person in front and select the app where it streams, and start playing.
NB: Every participant needs to have access to the content on their own device for this to work.
Watch video together during a FaceTime call
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6 FaceTime Features for Video Calls and Screen Sharing
How to schedule FaceTime calls, blur background, share screen, watch videos together, and use voice isolation