[Mount81]

Good question for AMD APU.

I hesitate between zidoo x20 and htpc with amd APU 

APU can play HDR , 4k files ? Have hdr to sdr conversion ? 

Thank

Here's an AVS Thread that I've made, dedicated to the same questions.
My conclusions so far -only based on the calculating opinions and SOME real user experience reports-, that it will do 4K / HDR fine up to 30fps for sure, but without any PQ enhancements with MadVR, or just with very minimal extra settings. The another -jet unanswered- mean and deal breaker dilemma would be the capability of the APUs for issue free and good quality SD, HD, and FHD upscaling to 4K res. Specially in the case of high framerate videos, like 50i / 50p and 60i / 60p. As can be read in this Thread, upscaling needs the most horsepower from the GPU when MadVR is concerned. The main scpetic opinions are based on the fact that these IGPs lack the access for any dedicated (and fast) VRAM, which would be important to MadVR to perform acceptable in these tasks. But again: not so much and not so sure real user experiences have been posted so far, to make any strict and excluding conclusion just yet IMO. 

And now my current questions regarding the general HTPC + MadVR Topic:

I've already posted these question in the AVS thread, but would like to ask them here as well, as the more relevant answers, the closer I could get to a relevant conclusion:

It sounds bad, that the AMD RX cards have problems with NGU. What does it mean in practice, in what cases is this seriously perceptible i.e. in the case of an 8GB RX 570? Will it affect much the SD (interlaced DVD) and 720p/50i and 1080/50i to 4K upscaling? And are the Vega cards completely free from this issue? (This last is rather just a curious question as they prices are rather in horror category and definitely out of the question for the budget I've planned.)

As I would rather choose an AMD card for my forthcoming HTPC, as I've read some other sites that they can do much better cadence perfect playback (playback at the more precisely correct Hz depending on the video's fps) and have generally less issues with Windows/drivers and HDR than the Nvidia cards do.

And another (repeated) question: will I have any relevant benefits with MadVR if I choose 8GB VRAM card compared to a 4GB one (SD, HD high framerate upscaling to 4K and/or general PQ enhancements, etc..) ?

Thanks for the replies!