I think it will show in whatever aspect ratio you upload.

It cares about overall pixel size, and for example standard 720x576 standard def 4:3 video will be brutally compressed compared to the exact same video upscaled using any non-AI upscaler (even nearest-neighbour) to 1440x1080.

I dug into this a bit a while ago, and could probably post my finding here if anyone was interested.