1732778 - Simulcast SSRCs aren't in encoding order when RTX is on

Status: RESOLVED FIXED

(Core :: WebRTC: Signaling, defect, P1)

Description

[Jonathan Lennox]

This is a bug exposed by the fix to #1727196.

When simulcast video is sent, prior to the fix to #1727196, the SSRCs are listed in the local SDP in the order corresponding to the configured encodings array.

After that fix, however (i.e. when RTX SSRCs are signaled), the primary (non-RTX) SSRCs are instead listed in numeric-order, irrespective of which encodings they correspond to.

This is a problem for Jitsi-Meet, because the Jitsi Videobridge needs to know which SSRC corresponds to which encoding, for proper encoding routing.

(The correct solution here would be to use rid header extensions, and we're working on that, but it'll be a while.)

It looks like the fix should be as simple as just printing the SSRCs (and RTX SSRCs) in mSsrcs order in JsepTrack::AddToMSection.

It'd be great if this could get fixed before FF 93 hits stable.

Comment 1

[Nils Ohlmeier [:drno]]

Attachment: Bug 1732778: sort SSSRC with RTX the same as without. r=bwc

Comment 2

[Nils Ohlmeier [:drno]]

Dry run looks good: https://treeherder.mozilla.org/jobs?repo=try&revision=24cace75c170c2170110d619c9cb7c25e86c852c&selectedTaskRun=cUaxqclJQZemoKgOAV4eiw.0

Comment 3

[Nico Grunbaum [:ng, @chew:mozilla.org]]

P1 so we can get it worked in for uplift.

Comment 4

[Nico Grunbaum [:ng, @chew:mozilla.org]]

S2 as it effects Jitsi in a non-trivial way.

Comment 5

[Nils Ohlmeier [:drno]]

Attachment: Bug 1732778: added unit test for verifying SSRC order

Depends on D126998

Comment 6

[Nils Ohlmeier [:drno]]

New try run to check if the modified tests are holding up https://treeherder.mozilla.org/jobs?repo=try&revision=753b2c6b819c5e4def73d7f0b5336835dfbee0a0

Comment 7

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/857e5d13da10
sort SSSRC with RTX the same as without. r=bwc
https://hg.mozilla.org/integration/autoland/rev/22fd68c02d1f
added unit test for verifying SSRC order r=bwc,ng

Comment 8

[Sandor Molnar[:smolnar]]

https://hg.mozilla.org/mozilla-central/rev/857e5d13da10
https://hg.mozilla.org/mozilla-central/rev/22fd68c02d1f