Since it worked fine in safe mode, I finally bit the bullet and did a factory reset on my phone. That worked, but as soon as I restored my backup, the problem came back, but this time I noticed that I couldn’t play any videos through the default player or the Google Photos app. Another search for video player problems indicated there’s an issue with the experimental video player, and to toggle the NuPlayer/AwesomePlayer settings in the developer settings. Violà!
I’m back to watching my Shaun the Sheep videos and all is right in the world once again.