[chrismorgan]

For regular viewers, the only pieces of functionality I can immediately think of that couldn’t readily be done sans-JavaScript are search autocomplete, annotations, end cards, auto-play (to the next video), and maybe quality selection (I’m fuzzy on what HLS actually lets you do, never actually worked with it).

Even things like voting and commenting are fairly straightforward to do basically, though you could do vastly better with an auto-resizing iframe (https://github.com/whatwg/html/issues/555) which would basically allow you to load new content into the document with a click (though it’ll clutter the history and make the back button behave surprisingly, see also https://github.com/whatwg/html/issues/6501 on that).