commit 75990b9a8f98ea2d597a31472fb778ec4d55f698
author Henrik Boström <hbos@webrtc.org> Mon Mar 20 09:09:04 2023
committer WebRTC LUCI CQ <webrtc-scoped@luci-project-accounts.iam.gserviceaccount.com> Mon Mar 20 10:41:15 2023
tree 8c166371fd91173634546627b235595d73b9279c
parent 12669513d24c0a39277f1c0bd296ccf71c0bb4b1

Ship ability to opt-in to VP9/AV1 simulcast.

With this unflagging, an app can opt-in to simulcast when using multiple
encodings by specifying RTCRtpEncodingParameters.scalabilityMode. This
ensures backwards-compat with apps relying on 3 encodings to mean SVC
who traditionally have not specified scalabilityMode.

It fixes the spec/API bug of asking for simulcast and not getting
simulcast. The field trial exists only as a kill-switch with a TODO to
remove it.

This ships initial support, however note that the VP9/AV1 simulcast uses
SimulcastRateAllocator (just like VP8/H264 simulcast). This rate
allocator uses more kbps than SvcRateAllocator. This should be revisited
to avoid significant higher bitrates, for example when comparing VP9
simulcast to VP9 SVC.

Shipping the ability for apps to opt-in makes it easier to exercise
these new code paths and allows initial feedback from developers, but
due to the high bitrate (= same bitrate as VP8/H264 simulcast today)
many apps may find that VP9 SVC is still more beneficial for BW reasons.

Bug: webrtc:14884, webrtc:15005
Change-Id: I748aae1adb47acc8a6b79b5852cff6aa47a46f5d
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/298046
Commit-Queue: Henrik Boström <hbos@webrtc.org>
Reviewed-by: Erik Språng <sprang@webrtc.org>
Reviewed-by: Evan Shrubsole <eshr@google.com>
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#39601}