tree 1bb1fdecdb6f0f4218870fc41605dd32287d96a7
parent 0d3dcc499767166b32a941abc9563e259ce1770f
author Henrik Boström <hbos@webrtc.org> 1727700110 +0200
committer WebRTC LUCI CQ <webrtc-scoped@luci-project-accounts.iam.gserviceaccount.com> 1727706015 +0000

Fix LibvpxVp9Encoder simulcast bug.

As of [1], a single VP9 encoder instance can produce simulcast 4:2:1.
When it does, the EncodedImage has its simulcast index set (0, 1, 2).

The bug is that if you then go back to a single encoder instance,
either because you're doing singlecast or because you're doing
simulcast with scaling factors that are not power of two (not 4:2:1),
then the simulcast index which was previously set to 2 is not reset due
to the old code path never calling SetSimulcastIndex.

Example repro:
1. Send VP9 simulcast {180p, 360p, 720p}, i.e. 4:2.1.
2. Reconfigure to {180p, 360p, 540p}, i.e. no longer 4:2:1.

What should happen: all three layers are sent.
What actually happened: 180p is not sent and the 540p layer flips flops
between 180p and 540p because the EncodedImage says simulcast index is
2 for both encodings[0] and encodings[2].

The fix is a one-line change: `SetSimulcastIndex(std::nullopt)` in the
case that we don't have a `simulcast_to_svc_converter_` that sets it
(0, 1, 2) for us.

[1] https://webrtc-review.googlesource.com/c/src/+/360280

Bug: chromium:370299916
Change-Id: I52bd4428bd12528f0e98869ec61626c06f589b43
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/363941
Reviewed-by: Sergey Silkin <ssilkin@webrtc.org>
Commit-Queue: Henrik Boström <hbos@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#43109}