Endless pliCount and nackCount

[cedricve]

We are using pion/webrtc in our open-source project, Kerberos Agent. We’re able to establish remote sessions through our TURN server, but when attempting to send RTSP streams at higher resolutions, we observe a continuous flow of PLI Count and Nack Count events.

Our logs show that ICE candidate pairs are successfully established, and data is indeed being transferred and received. However, all packets appear to be dropped. Interestingly, this behavior is intermittent—occasionally the stream does work.

After some experimentation, we found that lowering the video stream resolution significantly improves performance. Streams at 640x480 are decoded successfully without dropped frames, whereas higher resolutions like 1280x720 fail consistently.

We’re looking for guidance on how to address this issue. According to webrtc-internals, the connection is established successfully, data is flowing, yet every packet seems to be dropped, and the stream is never decoded in the browser.

An example of a working session (lower resolution):

An example of a connected session (higher resolution), without any decoding (after retrying new sessions it might happen that the stream still goes through):

[Sean-Der]

Hi @cedricve good to see you again.

One of the hops between Sender/Receiver is dropping packets because it is overloaded (or maybe explicitly configured to rate limit).

Pion can't do anything about this out of box. The best thing you can do is react to these stats about congestion. They are available in Go (or the browser) and move the user to a lower quality feed.

If you have ideas on how to make this better/more obvious I would love to hear! Also happy to debug in https://pion.ly/discord. I don't have a quick fix on this one unfortunately.

[cedricve]

Hey @Sean-Der, thanks! We're still promoting your work after many years ;) I just started testing with the interceptors which was missing from our code base, and it looks like much better (world of difference). It looks like the broadcast example is the only example taking into account interceptors, this might have done the trick.

https://github.com/pion/webrtc/blob/master/examples/broadcast/main.go#L50-L75

When adding this piece of code, we can achieve higher resolutions, and streams load much quicker/instant (black screen effect disappeared). I agree with your feedback, we might need to build adaptive transcoding if we see bandwidth is not capable to be send over.

Thanks a million, hope this issue might help other webrtc fans.