commit 3f10f657134c4e9dd2e3e1a48de7b7bcc020709b
author Philipp Hancke <phancke@meta.com> Mon Apr 15 23:36:38 2024
committer WebRTC LUCI CQ <webrtc-scoped@luci-project-accounts.iam.gserviceaccount.com> Mon May 06 19:20:48 2024
tree bfe0ce765264fbfe535c318ce73123c2147cc59d
parent 1e5f88c5be79c1e6ead624bf267ce5dd5e092019

sdp: answer with spec msid when msid support is unknown

this removes the reliance on the no-longer-spec a=msid-semantic lines
in case the offer did not signal any msid. Endpoints not supporting
msid should silently ignore the resulting a=msid: line. This also changes behavior such that a "legacy" offer without msid-semantic
line will be responded to with both msid-semantic and msid for any tracks present.
Plan-B ssrc-specific msid attributes are not signalled in that case.

See https://datatracker.ietf.org/doc/html/rfc8829#section-5.3.1
which includes it in the answer depending on the transceiver direction
but not if and only if the offer signalled a msid.

This also avoids recreating the stream and changing the SSRC
which could happen if the answer object was serialized to SDP
(which most unit tests do not do)

BUG=chromium:328522463

Change-Id: Id2f890b7756721d7c50460359950826d392483ae
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/346741
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Reviewed-by: Florent Castelli <orphis@webrtc.org>
Commit-Queue: Philipp Hancke <phancke@meta.com>
Cr-Commit-Position: refs/heads/main@{#42237}