If Playback doesn't begin shortly, try restarting your device.

Hi Matthew,

Thanks for reaching out through Apple Support Communities. We'd love to help sort this out so that you're able to enjoy your videos on YouTube and any other streaming service without issue.

To start, please let us know more about what's going on. Which web browser are you using when this occurs? Have you tried using a different web browser?

If the issue persists, will it be possible to join a different Wi-Fi network on your Mac to try again? This would help to isolate the issue further to either your network connection, or your Mac itself.

If it's still happening on another Wi-Fi network, you'll want to start your Mac in safe mode to see if the issue can be isolated further. The following guide explains how to start up in safe mode:

How to use safe mode on your Mac - Apple Support

If it's no longer happening in safe mode, you'll want to follow these steps to remove and test your login items, as one may be conflicting with video playback.

How to use safe mode on your Mac - Apple Support

We're here for you if you've got any questions.

Have a great day!