Select a youtube resolution and resize the player.
Sorry it took me a few days to reply. Unfortunately, I don't have access to a Mac and Safari has not been available on other platforms for a long time, which prevents me from looking directly into this. I can ask around and see if I can find someone who uses one to test, but nobody I know has one so it might be difficult to find.
But just because I can't look into it on my own doesn't mean we can't figure out what the problem is. To start with, I would like to know if you are getting any errors in the browser's javascript console, which should be somewhere in the developer tools. If you open the javascript console, then load youtube and trigger the error, and then give me the resulting contents of the javascript console, that would be helpful.
In addition, if anyone else who uses Safari can test to see if they also have the issue (to help verify that that the scope of the problem is Safari itself), that would be great.
No worries, thanks for getting back to me so quickly and thoroughly. I would have loved to help narrow this down, but as it turns out… it now works again. It's really odd, because I waited a few days before reporting a problem, and the problem persisted over browser (and even computer) restarts. But now that I wanted to look up errors in console etc. it just worked, and so far I have not managed to get it to break again. So I'll just turn this question into a happy rating then, because your script really makes my life much easier when using YouTube! :)
It could be another instance of youtube rolling out experiments on a small selection of users. Let me know if you run into it again, because even if it is a temporary problem I would like my script to be resilient to such problems in the future.
Excellent script that much improves QoL when using YouTube! :)
Original text: Seems to have stopped working yesterday – when the script is active, videos won't load for me, always getting a playback error instead. Latest Safari on current macOS version.