[astrange]

> exhaustively finding the best possible combination of QP/resolution pairs for an entire encoding ladder that also optimizes subjective quality – and not just MSE.

This is unnecessary if the encoder is well-written. It's like how some people used to run multipass encoders 3 or 4 times just in case the result got better. You only need one analysis pass to find the optimal quality at a bitrate.

[slhck]

Sure, the whole point of CRF is to set a quality target and forget about it, or, with ABR, to be as good as you can with an average bitrate target (under constraints). But you can't do that across resolutions, e.g. do you pick the higher bitrate 360p version, or the lower bitrate 480p one, considering both coding artifacts and upscaling degradation?

[astrange]

At those two resolutions you'd pick the higher resolution one. I agree that generation of codec doesn't scale all the way up to 4K and at that point you might need to make some smart decisions.

I think it should be possible to decide in one shot in the codec though. My memory is that codecs (image and video) have tried implementing scalable resolutions before, but it didn't catch on simply because dropping resolution is almost never better than dropping bitrate.