How would you do it if you had much more modest scale requirements? Say a few thousand simultaneous viewers. I'm kicking around an idea for a niche content video streaming service, but I don't know much about the tech stacks for it.
Bittorrent is built towards "offline" viewing. Try Peertube for a stack that is more built for streaming and has bittorrent sharing built-in (actually webtorrent, because the browser doesn't speak raw TCP or UDP, but the idea is the same)
Just use Nginx and a backend lang of your choosing.
I wouldn't bother. Unless you use storage at the CDN - which is probably very not cost effective for you.