HTML5 natively supports MP4 containers with H.256/ACC and WebVTT subtitles...
So that optimized browser streaming code is written by Google/Microsoft/Apple/Mozilla.
(Biggest problem with JS browser apps is poor memory management... which can kill user experience).

It should be trivial to convert to standard format before uploading content.

I like the way the Devs have thought this through...
And are focused on a great UI, decentralization and monetizing the webtorrent network...
As opposed to getting bogged down in technical rabbit holes.