[Galene] Re: Building a streaming gateway for Galène

[Juliusz Chroboczek <jch@irif.fr>]

> 1. PLI are working fine, and I can confirm that Galène manages to ask
> for keyframes.

Excellent.  This means you can reduce the rate of periodic keyframes to
something pretty minimal (like one per minute), and expect the stream to
recover within a second or so after a packet loss, even if NACK recovery
is broken.

> 2. NACK are received but ignored because my GStreamer webrtcbin element
> doesn't have "RTX" enabled.

Ah... right.  Galène doesn't use a separate RTX track for retransmissions,
it expects the client to honour retransmissions on the main audio track.

Let me explain.  There are two ways you can do retransmissions in WebRTC:
by simply resending the original packet, or by using an auxiliary "RTX"
track that is only used for retransmissions.  Since Pion v2 didn't support
RTX tracks, Galène takes the former approach -- this makes it slightly
more difficult to properly account for lost packets, but it's much
simpler.  Browsers support both, and are happy to retransmit packets over
the main track when there is no dedicated RTX track.

Now that Galène uses Pion v3, it should be possible to add support for
dedicated RTX tracks to it.  Don't hold your breath, though, I've got
a few deadlines looming and am very busy with other stuff right now.
Sorry.

-- Juliusz