For whatever reason, I can't make this play.

Could be OS related. Are you trying it on one of the Apple devices? I've tried it on Windows in FF and Chrome and Android phone and tablet. Please see youtube to html5 loader repo if you have issues loading a video. This is more for a demo purposes and not intended to have all youtube videos playback. In fact, some of them don't load into that video element due to copyright issues.

So strange, but it must be a browser issue on my end. Works with Chrome Version 90.0.4430.212 (Official Build) (64-bit), but not Chrome [Version 89.0.4389.128 (Official Build) (64-bit)]. Sorry for cluttering the comments with my user-specific issue!