Play 4k video on iMac - lagging

Discussion in 'iMac' started by Traktor, Nov 29, 2016.

  1. Traktor macrumors newbie

    Joined:
    Jan 20, 2011
    Location:
    Norway
    #1
    I have the cheapest 27" iMac late 2015 with 24 GB RAM. I have been trying to play some 4K videos but it just keeps lagging in both VLC and 5Kplayer. I use a Samsung T3 ssd as booth drive, where the video is stored as well. What can I do to make this work? The Mac should be plenty powerful.
     
  2. AlexGraphicD macrumors regular

    AlexGraphicD

    Joined:
    Oct 26, 2015
    Location:
    New York
    #2
    I am am not an expert but probably this has got to do with the weak m380.
    Now why would apple sell a 5k computer with a gpu that is not powerful enough to push those pixels is exactly what is wrong with Apple these days.

    If we have to buy the mid or the top spec model in order to enjoy smooth 4K videos then why does the base model exist in the first place?
     
  3. Traktor thread starter macrumors newbie

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    Jan 20, 2011
    Location:
    Norway
    #3
    Can anyone confirm this? It seems very strange to me.
     
  4. Espen Ekeroth macrumors newbie

    Joined:
    Nov 29, 2016
    #4
    I have the same issue on my 20.5" - it cant decode .265 codec in realtime. I have transcoded to .264 using handbrake, and then I can play it. It takes like 15+ hours to transcode a 2 hour movie.
     
  5. RedlegsFan macrumors 6502

    Joined:
    Mar 15, 2012
    #5
    The bad reviews regarding the 380 is exactly why I went to the mid tier model, 395
     
  6. Traktor thread starter macrumors newbie

    Joined:
    Jan 20, 2011
    Location:
    Norway
    #6
    Copied from apple.com


    "The new iPhone 7 shoots gorgeous 4K video. And on iMac with Retina display, both iMovie and Final Cut Pro give you the resolution — and responsiveness — to edit in 4K, turning your footage into a phenomenal viewing experience."

    If this iMac is capable of editing 4K video, how can I it be that I can't play 4K video?
     
  7. KnoeSS macrumors member

    KnoeSS

    Joined:
    Sep 5, 2016
    Location:
    The Hague, The Netherlands
    #7
    Probably because of this: iPhone recors in X264

     
  8. joema2 macrumors 65816

    joema2

    Joined:
    Sep 3, 2013
    #8
    All 4K video is not the same. You have not specified what codec your 4K video is, what bit rate, where you got it, etc. It is not possible to answer your question definitively without knowing this. However I'll speculate maybe it's H265.

    I edit and play H264 4K video on my 2015 top-spec iMac 27 every day, and it will even play on my 2013 MacBook Air.

    If by some chance you are talking about H265 4K, that is an entirely different matter. H265 is immensely more compute-intensive than H264. Even my top-spec iMac 27 cannot always play H265 4K without lag. This has little to do with the GPU per se, as H264 and H265 cannot be meaningfully accelerated by a GPU itself. The core algorithm is inherently sequential and not amenable to GPU-style parallelism.

    H264 and H265 encode/decode can only be accelerated with algorithm-specific hardware logic, such as Intel's Quick Sync, nVidia's NVENC or AMD's VCE. This logic is entirely separate from the GPU although in some cases it is packaged on the GPU card but accessed with a separate API. None of these are automatically used, but the application software must make specific API calls to use it.

    Ironically there are mobile devices with H265 hardware support integrated in a SoC (System On Chip) because the mobile market has rapid turnover and the large volume supports huge development budgets. The iPhone 6 and later use H265 for Facetime but not recording.

    To my knowledge the only camera that used H265 was the Samsung NX1 which is now discontinued. Behind the scenes there has been a huge conflict over intellectual property and licensing fees for H265/HEVC which has slowed the rollout, also Google offers their similar VP9 codec for free. These delays have allowed subsequent codec development to bring into question whether H265 is even worth it: http://www.streamingmedia.com/Artic...es/The-State-of-Video-Codecs-2016-110117.aspx
     
  9. Traktor thread starter macrumors newbie

    Joined:
    Jan 20, 2011
    Location:
    Norway
    #9
    Yes it is H265. Seems like I am out of luck then. I feel kind of cheated having dropped almost 2500 dollars for a computer I can't really use for what I wanted to. I also just bought a 4k tv that I can't really utilize now. So is the problem the CPU or GPU? Do you think the new iMac coming next year can play H265?
    --- Post Merged, Dec 1, 2016 ---
    Just downloaded hand break now. Seems like my iMac can do it in 6 hours, still a lot of time. I dont think I will keep doing this, and will probably just give up on 4K.
     
  10. joema2 macrumors 65816

    joema2

    Joined:
    Sep 3, 2013
    #10
    H265 (aka HEVC) allows the same resolution as H264 at 1/2 the bandwidth. However you don't get something for nothing. H265 is vastly more compute-intensive to encode or decode than H264. Real-time decoding generally requires dedicated hardware acceleration, not GPU acceleration. That means either Intel's Quick Sync or a GPU card with nVidia's NVENC or AMD's VCE, and software which supports that.

    IOW having the hardware doesn't help if the software doesn't support it. A good example is Adobe Premiere Pro which has not supported Quick Sync for years, yet Final Cut Pro X has. I believe Adobe recently started supporting it on Windows but not Mac.

    There are also multiple versions of all these hardware standards -- older versions of Quick Sync, NVENC and VCE support fewer codecs and encoding modes, whereas newer ones support more.

    The current Skylake CPU in many new iMacs supports H265 hardware encode/decode at 8-bits per color channel, so in theory given the right software a Skylake-equipped iMac could do hardware-supported H265 playback today.

    However it cannot do 10-bit per channel playback -- that is what Kaby Lake will do. In all cases you'd need software support for this. Knowing how your H265 video files are encoded would require investigation.

    Your first step should be evaluate all the playback software on the market and see if any Mac video player has hardware-accelerated H265 support that works on your iMac. This will involve investigation and possibly testing. Maybe VLC with some plugin would do that, or maybe you'll need to buy a player app which has Mac H265/HEVC hardware acceleration.
     

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