I'm aware of this project, but the demo doesn't work well, might just be slow access to video hosted on Chinese servers: https://github.com/sonysuqin/WasmVideoPlayer

I would be interested to sponsor development of a project that could reliably play large video files with different formats in the browser. I'd use it adapt our Chrome extension ('Language Learning with Netflix') into a website/SPA that could load in local video files, so you could study with movies from your hard drive. Contact email is in my profile. :-)