I’m writing this so if it ever happens again I don’t have to remember it, but rather can use google (I mean “google” in the generic sense, because of course I use DuckDuckGo).

 What search turned up didn’t help. This one from 2015 was all about Flash. This undated one says it can be YouTube servers, graphics drivers, or browser plugins. All possible and I poked around, but no luck.

I use Little Snitch, and that has caused weird things in the past, so I disabled it, and the problem was still there. Huh!

What I was seeing is that YouTube stopped playing videos – instead, I got the perpetual spinning white circle, then the message if the video doesn’t start playing, restart your device. I actually did that once, and it fixed it briefly, then it started (err stopped) again. Plus, restarting this machine is really disruptive — it’s my server for so many services: minecraft, owncloud, logitech Squeezecenter, deadwiki (and more?) Further diagnosis: QuickTime player and VLC also weren’t working – they started up, then stalled, just like YouTube. This is a pretty deep system-level issue. Of course I checked my networking – in fact, my son was using Zoom on his machine throughout, and I was able to use youtube-dl to fetch a video that wasn’t playing, then wasn’t able to play it using VLC.

So I tried to track it down. Quitting Steam and GoG Galaxy seemed to fix things, but only briefly. What else could it be? Well, I do have a number of Audio Output devices – I switched the System audio out to my TV instead of my USB D/A converter, and Boom- it started working! Switching it back to the USB D/A converter, and everything stopped – there’s our culprit. It’s hung somehow, not accepting data, and freezing threads trying to write to it. So I unplugged it from USB (thus rebooting it) and plugged it back in, and now all’s well again.