Why do 4K videos look bad on my new 5K iMac?

The issue is that you would need to use special processing to

upscale a lower res video to a higher res screen. Without that,

each pixel on the lower res image simply gets enlarged on the

higher res screen. So, unless the player has smoothing/scaling from

lower res to higher res, the results will look pixelated.

Depending on scaling algorithms used by a particular player, going

the other direction (high res image to low res screen) will look good.

If the players algorithm is very simple (just throws out pixels without

any sort of correction), it will look crappy.

Basically, a 5k screen cannot simply add pixels that don't exist

in a 4k image.

My personal opinion about 4K: it's not worth the hype. We bought a 4K TV this past year and I have never been so disappointed about the (lack of) picture quality. My old 720p HDTV had a much clearer, sharper, crisper display (and the colors were much better as well). We've had a new card installed after we complained for months (and it takes 3 months or so to get Samsung to actually get past their "automated troubleshooting" steps which we've had to do over and over again.) In any case, it doesn't compare to my old TV and, since it is much too late to return it, we will endure it and hope for an early demise so we can get a decent quality TV.

I'd attribute it to the fact that you have a superior quality display, but the quality of the movie is not. You generally get whatever quality it was when recorded.

Good luck!

same problem! do you have any updates