The iMac 5K has a gorgeous 14.2-megapixel 5120 X 2880 display, far larger than the 8.2 megapixels of 4K UltraHD video (3840 X 2160). And perhaps in a year or two, there will be an iMac 6K or iMac 8K.
And yet, here in 2015, it’s not possible to stream 4K from NetFlix or Amazon to a computer but it’s no problem to stream 4K video to a 4K TV. [Readers, please correct this statement if it’s wrong, but as yet MPG knows of no way to stream Netflix or Amazon 4K to an iMac display].
As far as MPG knows, this limitation has nothing technical about it; it’s all about content protection AKA DRM (Digital Rights Management).
It’s about time that Apple and/or Amazon and/or Netflix threw their considerable weight behind making 4K streaming (and full HD 1080p) possible on HiDPI and Retina displays.
Dimitry Y writes:
I would like to add my 2 cents regarding 4K Video support on iMac 27.
First, HEVC (x265) is the emerging standard for encoding high quality 4K videos, for both streaming and upcoming 4K BluRay disks. Second, in order to play HEVC files smoothly, a computer should support hardware accelerated HEVC playback.
In theory, Intel Skylake CPUs (used in new iMacs) do support hardware HEVC decoding, but unfortunately Skylake display support is limited to 4K (and iMac 27 display is 5K). AMD videocards, except the latest and very expensive Fury family, do not support hardware HEVC decoding. New NVIDIA cards such as GTX 950 - 980 do support accelerated HEVC playback.
Now in practice. I'm currently testing brand new Late 2015 iMac MK482LL/A, $2,299 USD retail. This is the top standard (not customized) config offered by Apple: 27" 5K, Skylake i5/3.3-3.9GHz, 8GB RAM, 2TB Fusion, AMD Radeon R9 M395.
I’m trying to open several HEVC (x265) 4K (2160p) sample movie trailers in MP4 format; each about 300-500 MB in size, 1-2 minutes in length. They are DRM-free and can be dowloaded from here:
On my iMac 5K, Apple QuickTime Player would not open any of these files. VLC player opens all of the trailers fine, but it plays extremely choppy and unwatchable video, at the same time overloading all 4 CPU cores 100%. In addition, I'm trying MPV player (open source project, https://mpv.io). To force hardware acceleration (and color management), I'm launching it via Automator with the following options:
open -a mpv.app --args --vo=opengl:icc-profile-auto --hwdec=auto
Alas, the same result as with VLC player: 100% CPU overload and choppy unwatchable playback.
Conclusion. It appears that iMac 5K does not support HEVC hardware acceleration. Now, the big problem is that you can not upgrade videocard in iMac 5K, and you can not even use it in Target Display Mode. So, I don't think that current iMac models would ever be able to play HEVC 4K videos. And that's why I'm going to return my iMac to Apple and wait for a next year model. Fortunately, Intel promises 5K HEVC hardware decoding in Kaby Lake CPUs coming in 2H 2016.
I feel sorry about this, because iMac 5K is a great machine and its 5K DCI-P3 display is simply the best available. I hope that I'm wrong about iMac 5K not supporting hardware HEVC. So please give me the good news and tell me how to smoothly play HEVC videos on iMac 5K.
MPG: Ouch. Even if decodable, 4K on a 5K display would only use about 60% of the screen (without upscaling), so that’s a bummer.