We've received multiple reports of difficulty with motion backgrounds and videos on the latest version of macOS. Videos and motions either do not play, or only play once they've been selected multiple times.
We have reproduced the problem, and believe the latest version of macOS is responsible (10.13.4).
Motion backgrounds and videos work as expected on version 10.13.3. If you go On Air with a Mac, do not update to macOS 10.13.4 for now.
If you've already updated and are experiencing difficulty, consider replacing your motions with still backgrounds, or use another computer if you have one.
