[Galene] Re: fq-codel trashing

[Juliusz Chroboczek <jch@irif.fr>]

>> We just had a meeting with 70 people and at around 40 cameras switched on,

> Which send quality were they all using? "normal"?

The quality selected in the menu is the maximum allowable quality; Galène
will rather eagerly drop down beneath it, all the way down to 200kbit/s
(it will drop quality even more aggressively in the future).  So we were
running at "normal", but the resulting bitrate was somewhere between "low"
and "lowest".

> Frankly I understand only ~5% of what you're talking about in this thread.

Yeah, that's also our case.  This doesn't prevent us from speaking, though ;-)

> But do you really expect all users' end devices to decode 40 video streams?

[...]

> In my local tests with slow and ancient 10+ years old laptops I even get
> video drop-outs within my LAN with only 3 video streams.

At lab meetings, everyone has got rather nice laptops, and Galène works
reasonably well up to 25 videos or so, except for the elegant people with
the fancy fanless MacBooks.

The situation is different at lectures, of course, but then the students
are not too keen on switching their cameras on.  (Back in December,
a student who wasn't reacting to a question admitted to being busy with
frying eggs.  I naturally accepted his excuse as perfectly legitimate.)

> Not to speak of all the crappy Internet connections, already over-loaded
> while other family members are watching Netflix or similar situations in
> shared flats.

Galène should in principle drop the quality down when a link is congesed.
We're currently dropping down to the lowest rate that everyone can tolerate
(but not beneath 200kbit/s), with simulcast or SVC, as discussed in
a previous mail, we'll be able to send different qualities to different
users.

> We had one hearing impaired user who hears a little bit with in-ear
> devices. Normally the user also follows spoken text by lip-reading to
> get more context. But this is nearly impossible for her in a video
> session because audio and video are not sufficiently synchronised with
> our setup.

Hmm... was that with Galène?  Which browser?

In principle, Galène generates all the bits of protocol to perform
accurate lipsynch on the receiving side.  I have veryfied that it works
well with Chrome.

> Not sure whether that's really a fairness issue within Galène. I can see
> differing latencies in /stats for different connections. The connection
> with higher latency, most times on all "Down" streams, has the higher
> latency consistently throughout whole session. I suspect the receiver
> side is the issue.

You might be mis-reading the statistics.  For an up stream, Galène only
keeps track of the amount of jitter.  For a down stream, Galène keeps
track of both average delay and jitter.

Up:   ±3ms     means 3ms average jitter;
Down: 30ms±3ms means 30ms average delay with 3ms average jitter.

>> At the highest point, Galène was at 270% CPU, and the TURN server was
>> using another 50%.  That's on a four-core VM.

> I'm far away from such a setup. So I wonder whether my response is
> useful at all.

It's very useful.  We want Galène to scale all the way from a single core
ARMv7 (thanks for the Beaglebone, Dave) to a 16-core, 32-thread server.

-- Juliusz