An Introduction to WebRTC Simulcast • Hacker News Board

Re: An Introduction to WebRTC Simulcast

#11

Post by davidz » Tue, Sep 21, 2021, 4:40 AM UTC

Benjamin_Dobell wrote: post #2

This approach of the broadcasting "peer" sending multiple streams (with varying bitrates) to a relaying server is a neat solution. This is done to avoid transcoding on the relay servers, so it makes the servers cheap. It is superior to: > Lower[ring] the bitrate of everyone’s streams so it doesn’t overwhelm the slow user (i.e. the lowest common denominator) However, it's still a lowest common denominator solution wit…

> However, it's still a lowest common denominator solution with respect to what codec is being used. The broadcasting "peer" has to send using a codec that every other peer supports. Essentially that means you're stuck with the lowest common denominator codec.

This is correct, though I wouldn't call them "inferior codecs": all WebRTC capable browsers support both H.264 and VP8 as required by the specs.

Re: An Introduction to WebRTC Simulcast

#12

Post by pthatcherg » Wed, Sep 22, 2021, 12:58 AM UTC

That's a well written article covering the basics of simulcast.

If you're interested in seeing an implementation of an SFU doing simulcast forwarding written in Rust, we (at Signal) recently open sourced our SFU:

https://github.com/signalapp/Signal-Calling-Service/blob/mai...

Re: An Introduction to WebRTC Simulcast

#13

Post by pthatcherg » Wed, Sep 22, 2021, 1:02 AM UTC

Does anyone know where LiveKit's implementation of congestion control is? I can't find it looking through their code and to me that's a major sign of the maturity or completeness of an SFU. For example, Jitsi, Signal's SFU, and (I think) MediaSoup have it. But I've not yet seen a pion-based implementation of congestion control and I'm hoping that LiveKit has fixed that. But I can't find it.

Re: An Introduction to WebRTC Simulcast

#14

Post by MayeulC » Thu, Sep 23, 2021, 3:56 PM UTC

Sean-Der wrote: post #6

MayeulC wrote: post #5

Earlier quoted context omitted.

I would really like to see some projects that leverage SVC, as I haven't seen a single example (and ffmpeg doesn't support them).

I believe Galene does[0] Juliusz was working on pion/RTP for it. You can see all the details here [1] [0] https://github.com/jech/galene [1] https://github.com/pion/rtp/blob/master/codecs/vp9_packet.go

Thanks a lot for these pointers!

Re: An Introduction to WebRTC Simulcast

#15

Post by jech » Sat, Oct 02, 2021, 2:27 PM UTC

Sean-Der wrote: post #6

MayeulC wrote: post #5

Earlier quoted context omitted.

I would really like to see some projects that leverage SVC, as I haven't seen a single example (and ffmpeg doesn't support them).

I believe Galene does[0] Juliusz was working on pion/RTP for it. You can see all the details here [1] [0] https://github.com/jech/galene [1] https://github.com/pion/rtp/blob/master/codecs/vp9_packet.go

Yes, Galene 0.4 and later uses SVC by default when the following conditions are satisfied:

  * the sender is using a Chromium-like browser (the receiver may be Chromium, Firefox or Safari);
  * the codec is either VP8 or VP9;
  * there are at least three users in the group.

You can see a demo at https://galene.org:8443/group/public and https://galene.org:8443/group/public-vp9 (any username, empty password).