Is there a reason not to use ffmpeg's -vf scale=wxh:flags=lanczos ?

[Boteium]

I think the downscale part can be done by ffmpeg's lancoz downscale filter and remove the need to re-scale it by python. It's much faster and efficient. The downscale and encoding process can be done together in only one step. There is really no need to add parallelism in python in the next version when ffmpeg can already do that.

[k4yt3x]

Sounds like a nice idea, I'll try implementing that.