Video conferencing with Jitsi

Posted Mar 25, 2020 15:10 UTC (Wed) by sorokin (guest, #88478)
In reply to: Video conferencing with Jitsi by niner
Parent article: Video conferencing with Jitsi

> it scales O(n) and works just so much better

I don't quite understand this. Even if all video streams get aggregated into one connection from server, that single connection still transmits n times the data.

My understanding is that total required bandwidth should be the same in both cases. Perhaps central server works better when participants' upload speed is limited?

Video conferencing with Jitsi

Posted Mar 25, 2020 15:23 UTC (Wed) by niner (subscriber, #26151) [Link]

It's quite possible that I misunderstood why the video bridge helps so much (which it does). It could simply be that the video bridge is a workaround for the Firefox issues mentioned in another comment. The linked hackernews discussion indicates that with peer-to-peer as soon as a Firefox user joins the meeting, performance is degraded for all participants.

It's also likely that you're right and the central server mitigates notoriously limited upload speeds of DSL and mobile (and sadly, where I live, even cable) connections.

Video conferencing with Jitsi

Posted Mar 25, 2020 15:41 UTC (Wed) by excors (subscriber, #95769) [Link]

From https://jitsi.org/jitsi-videobridge-performance-evaluation/ it sounds like the key for scalability is the "last N" mode. The bridge receives streams from all participants, but only broadcasts the streams from the N most recent "dominant speakers". That means the bridge's traffic scales linearly with the number of participants, and a client's traffic scales with N (which is a small constant).

If you don't use that mode then I think it's O(num_participants^2) on the bridge and O(num_participants) on the clients, though with better constant factors than peer-to-peer: each client only has to upload their stream once to the bridge (vs num_participants-1 times to every other peer), which is good since clients usually have much lower upload bandwidth than download.