This involves adding a new crop setting: ‘Fill’, accompanying ‘Crop to Fill’ and ‘letterbox/pillarbox’ so that the rescaling indicated by the required resolution is applied, although this usually warps the image. The modification on the underlying ffmpeg command is very simple, for example for 8K output:
..., scale=w=7680:h=4320:flags=lanczos:threads=0,split=2[out1][out2], ....
I’ve tried it from command line and the result is the expected.
This would allow the deformation introduced by anamorphic lenses to be corrected in the same step.