[Galene] Re: Building a streaming gateway for Galène

[Juliusz Chroboczek <jch@irif.fr>]

> For the past two weeks I have been working on streaming from a
> broadcasting software such as OBS-Studio (that uses FFMpeg) to Galène.

This would be a great addition!  We have quite a few users that use OBS,
and, as you mention, going through the v4l virtual camera has some
disadvantages.

> 0. Using OBS Virtual v4l2 camera, but it is not portable and has audio
> sync issues.
> 1. Streaming to a gateway that will initiate the WebRTC session with Galène.
> 2. Implement WebRTC support in OBS-Studio as an output plugin.

I would tend to agree, (1) is probably the best solution, since it avoids
bloating either Galène or OBS.

> Last week I tried to implement a gateway using GStreamer webrtcbin
> plugin, <https://github.com/erdnaxe/galene-stream>. Although I am able
> to stream to Galène, I observe video drops. I am circumventing the issue
> by forcing the VP8 encoder to insert a keyframe every 5 frames, but that
> seems a terrible hack.

I'll have a look at your code as soon as I have some time.  In the
meantime, there are three things that you need to do:

1. send periodic RTCP Sender Reports with accurate NTP times;
2. react to RTCP PLI packets by inserting a keyframe;
3. react to RTCP NACK packets by resending the packets listed in the NACK.

(1) is essential for proper lipsynch.  (2) is what allows a stream to
recover after a catastrophic loss event.  (3) is what allows a stream to
recover rapidly after moderate amounts of loss.

> Right now [...] I don't know if I should...

I'll have a look, think it over, then get back to you.

-- Juliusz