Simulcast on / off

Hi, I have a question concerning the simulcast option. We experienced on our own Jitis installation a significantly better video quality if we turn simulcast off. In my test sessions and for the most of the sessions of our users bandwith is a non issue, so I would have expected, that the simulcast videoquality uses a high quality stream / layer. But with simulcast despite video resolution being the same as without, the bitrate is half as high so the compression must be higher and we get many compression artifacts. Why is this the case and ist there a possibility to force lower compression accepting higher bandwith usage with simulcast, too? I guess the bandwith detection has an influence on the chosen compressioin rate? The actual bitrate is much lower than the maximum values defined in “maxBitratesVideo”.

Maybe I just oversaw, that this topic has already been handled. Would someone please be so nice and point me towards the right thread, if that is the case.

My main question is, if it is possible to reach the same quality with simulcast as without simulcast if bandwith is no issue. In my case I get always worse video quality with simulcast turned on.

Thanks in advance …

In theory this should be possible, in practice it depends on many factors. As your question is rather generic and there is no information about your exact configuration, I can only suggest experimenting with a few settings to narrow down you rissue:

  • check if BWE on the videobridge is indeed the culprit by disabling taking BWE into account. You can do so by changing jvb.conf to include trust-bwe=false in the cc section, e.g.:
videobridge: {
    cc {
        trust-bwe=false
    }
}
  • I’ve also read some reports about BWE being off/unreliable when not using websocket as bridge datachannel. May be worth checking unless you already are using websockets (I believe it is the default nowadays?)
  • experiment with onstage-preferred-height and onstage-preferred-framerate settings in jvb.conf. As far as I understand, a video track with a height > onstage-preferred-height will not be forwarded to other clients unless it also fulfills the onstage-preferred-framerate setting. So it may be worth a try to set onstage-preferred-height=720 instead of the default 360.

Of course, other factors such as the browser and webcam used, client CPU performance and client’s upload bandwidth do play a considerable role and should be considered when testing these settings. Similarly, p2p may differ from multiparty calls that are routed via the bridge.