Handling Transport-Wide-CC Feedback in a Custom Janus Plugin

General
1

Hello,

I am currently developing a custom plugin for Janus, similar to the VideoRoom plugin. In my scenario, I have two publishers, A and C, and a subscriber B who subscribes to A’s video stream.

My question is about handling the transport-wide-cc feedback from B. When B sends transport-wide-cc feedback to Janus, should I relay this feedback to the publisher A in my plugin? Or does the Janus server handle this feedback internally?

I understand that in most cases, the publisher (a WebRTC client) would handle congestion control, including adjusting the bitrate of its media stream. However, in my scenario, I am considering whether I need to relay the feedback to the publisher for it to adjust its bitrate accordingly.

Any guidance or advice would be greatly appreciated.

Thank you.

2

We don’t support TWCC on the subscribers side yet, only publisher. For publishers, this is handled by the core, so plugins are not involved.

3

Thank you for your response. Given that Janus currently does not handle TWCC for subscribers, I am considering alternative approaches for managing network congestion in my custom plugin.

One approach I am considering is to use the slow_link callback function to detect when the subscriber is experiencing network issues. Once detected, I am thinking of two possible ways to adjust the bitrate:

  1. Send a REMB packet to the publisher to request it to lower its bitrate.
  2. If I use an SVC (Scalable Video Coding) encoder, dynamically select a lower-quality layer for the stream.

Would these approaches be feasible in the current Janus architecture? Any advice or suggestions would be greatly appreciated.

Thank you.

4

Yes, using slow_link or info you get from getStats() can be used as your triggers to react somehow, until we implement bandwidth estimation on that side too.