That video is fine here at 3840 x 2160 in IE/Chrome using DP cable.
Managed to take a video
https://youtu.be/SBAnB26HkyA
52 seconds in is what i'm trying to explain! If you look closely at the woman's chin, you'll see the pixels.
That looks like compression artifacts, which you'll be getting on this sort of content. That isn't the monitor's fault.