Live broadcast requires RTMS (media server) of some kind, like Wowza or Red5pro. There's also quite a bit of management tooling required to prevent abuse. Rocket.Chat doesn't do it. 

One option is to use Jitsi video bridge or just Jitsi Meet and broadcast via YouTube. 

If you'd be interested in setting it up for your site, we can discuss custom configuration. At this stage live video streaming for default package would bring too much complexity for setup and support, so we don't do it yet.