1. It's hard to give constructive help without more information. Why not write a script that compiles a bunch of pages into html? As the other comment said, there's also stuff like jekyll. Maybe you could provide some use-cases?
2. Explain your use-cases? Why not call ffmpeg directly? You'll need to familiarize yourself with the original library functionality anyway, no?
3. No opinion. Not particularly interested in games. Might be hard to generalize, maybe?
4. Versatile in what sense? What are your complaints with existing media formats? I think licensing is an issue, but stuff like VP9 and Opus seem to take care of that matter. I'm not an expert, but I think both MP4 and MKV can already hold an unlimited number of media files.