Interesting enough, I'm probably one of the few people who still has some theora videos on the web in some very old blogposts of mine.<p>Some history for people who are not aware: Theora became somewhat popular in free software / open source circles, because at the time, it was the best codec which was believed to be either free of patents or the patents were explicitly opened up for free use. Therefore, if you were concerned about patents and their impact on free software, you'd use it. But Theora wasn't a great codec, which we always knew, it just was the best we had before google bought and opened up VP8.<p>It's an interesting tradeoff. Theora was never particularly popular, so you probably will have a low number of sites being impacted. But we kinda have a tradition that the web plattform rarely breaks things. You mostly can still use old html from 20-30 years ago, gif will probably stay supported in browsers forever, and I don't think there are many examples of media formats in browsers being deprecated. Even odd things like bmp are still supported.