Whenever movie frame encoding needs to be in non-RGBA format (pretty much
always, e.g. H.264 uses YUV etc.), the ffmpeg code has been using
sws_scale() since 2007. But that one is completely single threaded.
It can be multi-threaded by passing "threads" option to SwsContext
(in a cumbersome way), combined with sws_scale_frame API. Which however
requires frame data buffers to be allocated via AVBuffer machinery.
Rendering a 300-frame part of Sprite Fright Edit (target H.264 Medium):
- Windows Ryzen 5950X: 16.1 -> 12.0 seconds (generate_video_frame part
4.7 -> 0.7 sec).
- Mac M1 Max: 13.1 -> 12.5 sec. Speedup is smaller, but comparatively,
entirely other part of movie rendering (audio resampling inside audaspace)
is way more expensive compared to the windows machine.
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