Hi RoxyGuy,
If you haven't done so yet, restart your Mac and test the movie again. This step may seem fairly simple, but it can refresh the connection and macOS which may help correct the issue. Although the title of this article doesn't fit the description of the issue, the steps could still be helpful: If an app on your Mac stops responding, closes unexpectedly, or won’t open.
"1. Quit and reopen the app
Quit the app, then open it again. If the app won't quit, force the app to quit. Then check to see if the problem with the app is fixed.
2. Restart your Mac
Restart your Mac. Then check to see if the problem with the app is fixed.
3. Check for updates
To see if updates are available for the app, open the App Store, then click Updates. If updates aren't available for the app, update the software on your Mac. Or if you didn't get the app from the App Store, look for updates to the app on the app developer's website. Then check to see if the problem with the app is fixed.
4. Reinstall the app
Delete the app. When you do this, you might lose data that was stored in the app. Then redownload the app. If you didn't get the app from the App Store, redownload the app on the app developer's website. Then check to see if the problem with the app is fixed."
If the issue persists, reach out to Apple Support directly so they can look into this with you further. They can be contacted here: Contact Apple Support or by calling the most applicable phone number from this list: Contact Apple for support and service.
Regards.