The thing about it is, is that 4K isnt generic. 4K specifcally means the resolution. What matter also is what codec is used, what level/profile is used, what frame rate etcetc.
Most 4K consumer content will be encouded in HEVC. There will be two main types. I imagine the most popular one will be HEVC L52 MAIN 10. I have sample of L52 MAIN 10 HEVC in
4K@60 FPS and playing this is the current build of PDVD 15 is a stuttering mess. The reason is, PDVD15 has no GPU acceleration for high colour footage. It does work for example with MPC-HC FFMPEG Lav Filters, where it can do DXVA2 GPU acceleration in both copyback and native modes. I imagine this will be the most common as its what the UHD bluray spec uses and the content producers will no doubt target that.
Only a Geforce 960 and 950 currently support full hardware decoding of HEVC 4K content in the video engine of the chip. Theres no way any CPU will do realtime HEVC L52 MAIN 10
4K@60FPS.
The other one of the two types, is lower 8 bit colour encoded HEVC. With say a sample of HEVC L51 4K @60FPS I can do PDVD15 playback accelerated through my GPU (well the current build of PDVD15 is broken for me but assuming thats fixed and I have been able to do it in the past) just fine. It also works with the usual open source players too.
Thats why I gave those examples in my first response