[Broadcaster] Send PLI fails sometimes

[sgfn]

[mickel8]

Sometimes, browser doesn't start immediately sending all layers. Instead, it has to probe the connection. This means:

• we cannot send PLi request before receiving the first packet for given layer as some SSRC
• viewer has to wait additional time until browser starts sending h layer

Two things are actionable:

• start sending whatever layer we have and then upgrade when better layer appears
• why browser sometimes need to probe the connection and some other time it does not

[mickel8]

why browser sometimes need to probe the connection and some other time it does not

This might have something to do with the frequency of TWCC repors we are sending. From video-dev slack:

It's very sensitive to the timing derived from TWCC packets. If you make a mistake in how you generate those or if you send them too slow I can see why it would sometimes behave like that 

https://video-dev.slack.com/archives/C9PQ6FWH3/p1727878788799169?thread_ts=1727873414.829029&cid=C9PQ6FWH3