A very high pixel density makes a real difference when you're looking at printed text and, in general, images with very sharp lines. That's not what VP9 or HVE

A very high pixel density makes a real difference when you're looking at printed text and, in general, images with very sharp lines. That's not what VP9 or HVEC are good for anyway, so I would bet that scaling down 4k video or scaling up 1080p (for the same bitrate) won't make any noticeable difference. But of course that's just a matter of opinion unless we do a blind test with real use cases.