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CMS - What causes the bad presentation quality? (Example attached)


Hi community

Observed behavior (MS Edge, Chrome):

  • Video streams of participants usually are crisp and clean (except their connection is bad)
  • Presentation often suddenly starts looking as if it got shredded in the lower third of the image


Example of the problem:



Any technical suggestions what we could be looking at here? It always draws that kind of pattern where the lower part of the image seems to be turned into those huge square pixels.

  • Packet loss?
  • Codec doing something funky?
  • Delayed I-Frames, P-Frames, B-Frames?

I kind of suspect QoS issues/misconfiguration but have a somewhat hard time to proof it to the network team. When joining the meeting through a smartphone (cellular network) the presentation looks crisp again.


Another thing that would be helpful for educational purposes @people that have CMS running and can do presentations smoothly:

Would you be willing to open edge://webrtc-internals/ during an ongoing meeting and take a screenshot of the various graphs (incoming RTP stream of the presentation)? I'd be curious how some "good" reference stats of a smooth presentation should look like. 

Below is what it looks like in our setup when I share a simple Excel sheet in a presentation and scroll around in it a bit. On the receiving end the grid of the cells is gone most of the time and it just kind of looks like a pixelated, laggy, blurry soup. When I stop scrolling it takes 2-3 seconds until quality is adjusted. Interestingly with MS Teams presentations work flawlessly (I mention it because I think both are based on WebRTC technology when using the browser).

2022-09-13 10_09_48-WebRTC Internals.png


Anyone else ever experienced similar issues? And got it fixed? Any feedback / suggestions are welcome. 


Best regards

1 Reply 1


Just wanted to bump this with an update.

  • We've upgraded to CMS Version 3.7 (Currently latest version)
  • Problem of bad presentation quality persists (Check screenshot below, all presentations look more or less like that)
  • In CMS 3.7 there are some neat new stats -> We noticed that the presentation stream always has a much higher jitter rate than the video streams for no obvious reason (in the screenshot it's "only" 218ms, it occasionally spikes up to 1500ms while the video streams always stay below 10ms)
  • CPU of client machines spikes when we share screen (Intel® Core™ i7-10700 -> screen sharing causes + 25-30% CPU load, on a bit older machines it's quite a bit more load)
  • Issue seems to be browser related (chromium to be precise)
  • Meeting Server 1000 platform looks perfectly healthy when the problems occur (CPU <5% load, RAM, network load, etc. all look fine)
  • Problem persisted even when clients were hooked up to the same switch as CMS (video now with <1ms jitter, presentation jitter still all over the place)
  • jitter on iperf streams between client / server is perfectly fine. In wireshark we see a straight line with max. throughput (same port ranges, same dscp tagging) (sidenote: make sure your iperf versions on client/server match otherwise you'll run into issues)
  • We checked if we're affected by faulty RAM (we're not. Check FN 72368)
  • We checked the quality settings but most of them don't apply to the webbridge anyway
  • Problem doesn't seem to occur on mobile devices (iOS Safari, Webkit rendering engine)
  • Changing congestion algorithms on the ESXi host ("New Reno" vs. "CUBIC") has no impact on presentation quality in CMS 


CMS Presentation quality still badCMS Presentation quality still bad


By now we suspect that the clients themselves / the browser might be the bottleneck. Since Zoom, MS Teams, Jitsi are all working fine we're kind of lost and out of ideas. Idea donations about what we could investigate or how we could tackle the bad presentation quality would still be welcome.


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