* [Galene] About VP9 SVC in Galene
@ 2021-08-04 10:33 Juliusz Chroboczek
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From: Juliusz Chroboczek @ 2021-08-04 10:33 UTC (permalink / raw)
To: galene
Hi,
I've spent the last two nights implementing spatial VP9 SVC in Galene
(temporal was already working fine). I think it's correct, although not
quite optimal.
In order to test, set up a group with VP9, enable simulcast, and then
toggle between « Receive: all » and « Receive: all (low) ». You should
see the quality change without any visible artefacts and with no
renegotiation. (It is normal to see a temporary degradation in quality,
due to the second point below.)
Two issues. First, once in a while Chromium's rate estimator gets stuck
in a state where it's sending a very low data rate; the only fix appears
to be to restart the stream. I've spent hours trying to debug the issue,
and I don't see anything wrong with my code.
Second, we're not parsing the dependency descriptor, which means that we
cannot switch seamlessly at arbitrary points. The result is that we
require a keyframe when a switch is required, which causes extra traffic
and a visible degradation in stream quality. I think this is good enough
for 0.4, especially as we currently tend to prefer temporal degradation
when we're congested.
-- Juliusz
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