commit 2fec64484f0c1355db1dde236c3c205985a30a30
author Henrik Boström <hbos@webrtc.org> Thu Jun 15 10:49:26 2023
committer WebRTC LUCI CQ <webrtc-scoped@luci-project-accounts.iam.gserviceaccount.com> Thu Jun 15 12:48:48 2023
tree 963a257fc979d222e2cba56015dddbb23895bc43
parent bd14a73f81cdb92f7b8098ed026b1c687ee78613

Fix L1Tx target bitrate bug when the standard API is used.

There are now multiple ways to configure VP9 L1Tx:
- Legacy API: configure legacy SVC and disable encodings, this gets
  interpreted as disabling spatial layers (non-standard API hack).
- Standard API: configure scalability_mode. This can be done either
  with a single encoding or multiple encodings. As long as only one
  encoding is active we get a single L1Tx ssrc, same as legacy API.

Due to a bug, the ApplySpatialLayerBitrateLimits() logic which tweaks
bitrates was only applied in the legacy API code path, not the standard
API code path, despite both code paths configuring L1Tx.

The issue is that IsSimulcastOrMultipleSpatialLayers() was checking if
`number_of_streams == 1`. This is true in legacy code path but not
standard code path. The fix is to look at
`numberOfSimulcastStreams == 1` instead, which is set to the correct
value regardless of code path used.

This CL adds comments documenting the difference between
`number_of_streams` and `numberOfSimulcastStreams` to reduce the risk
of more mistakes like this in the future.

Bug: chromium:1455039, b:279161263
Change-Id: I69789b68cc5d45ef1b3becd310687c8dec8e7c87
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/308722
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Commit-Queue: Henrik Boström <hbos@webrtc.org>
Reviewed-by: Erik Språng <sprang@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#40287}