In simulcast, BW adaptation causes layers to be disabled rather than
downscaling layers. But CPU adaptation restricts the resolution of all
layers, this means that a 540p restriction on 180p:360p:720p results in
180p:360p:540p, which is fine but a) it's inconsistent with BW
adaptation and b) it's not ideal for performance, because non power of
two scaling factors means we can't use a single encoder instance to
produce all layers (the CPU adaptation could actually result in even
more CPU usage and further adaptation as a result).
This CL disables top layers by limiting `max_num_layers` based on
`restrictions_` and the layers' `requested_resolution`, the end result
is 180p:360p:- when CPU adaptation kicks in.
Note that the problem described (and therefore the solution) is
specific to the `requested_resolution` API. If instead the
`scale_resolution_down_by` API is used, all scaling is relative and we
get 135p:270p:540p, which is problematic for other reasons (180p and
360p no longer sent, middle layer no longer HW accelerated).
Bug: webrtc:366415118
Change-Id: I2e238b1b87470413c21623b21d0ce20eadf6c8c7
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/364660
Commit-Queue: Henrik Boström <hbos@webrtc.org>
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#43172}
b23b3dd9b1