TODO: build a local-first livestream remote conference zoom alternative software
But I got a mumble server up and running in no time flat, so it works that way, and the audio quality is amazing - far better than Zoom - as long as everybody's wearing properly-configured headsets.
Federation isn't needed because you don't need to have servers that communicate with each other, you just need some server that can host a given video call. So any open source solution works, no federation architecture is required.
You put a repeater on (at least) one side of every bottleneck to remove redundant traffic.