983e8f0100 resulted in the correct
dimensions, but it was not actually right because vo_gpu_next still had
the src and dst rects the same. This just needs to work like how vo_gpu
does where the src is the image params and the dst is desired output. So
basically, just copy that code over here. Fixes#12108 and as a bonus,
overriding the aspect ratio now results in correct screenshots
(previously didn't work at now and then with the above commit it had
correct dimensions but still incorrect output).
efefe3a6dc