Final Cut Pro Not utilizing everything my iMac Has

Discussion in 'Digital Video' started by adamjackson, Apr 2, 2018.

  1. adamjackson macrumors 68000

    Jul 9, 2008
    I'm tired of waiting 2-3 days for my iMac to transcode 4K Video knowing it has more to offer that FCP isn't utilizing.

    iMac 5K Core i7 4Ghz w/ 32GB of RAM, Raderon 395X and 3 terabyte Fusion drive.

    [​IMG] [​IMG]


    It's been 24 hours since I started encoding 600 gigabytes of 4K files off multiple cameras. FCP is only maxing out at 100% CPU (1 out of 8 cores) as i have iStat Menus pro set to 800% as maximum and it's not touching the Radeon processor. It's not even hot air coming out of the back.

    All of the files are stored locally. I/O isn't being taxed at all. I have every application closed on this mac except Safari and FCP. I want FCP to use every bit of processing power the iMac has. It'll take a week to transcode these videos at this rate. Why is it so slow? how can I fix this?

    FCP 10.4, latest version of Mac OS.
  2. Darmok N Jalad macrumors 65816

    Darmok N Jalad

    Sep 26, 2017
    Are you encoding to H.264? If so, it might be using Intel QuickSync, which uses the Intel GT GPU. You'd have to download Intel's Power Gadget and watch the "GT" frequency to see if it's hitting the IGP.
  3. adamjackson thread starter macrumors 68000

    Jul 9, 2008
    The source files are h.265 & HEVC.

    Here's the import settings for all 715 files:


    Downloading Power Gadget Now
    --- Post Merged, Apr 2, 2018 ---
    Power Gadget while FCP is running:

  4. Darmok N Jalad macrumors 65816

    Darmok N Jalad

    Sep 26, 2017
    Yeah, it doesn't appear to be leveraging the GPU at all. Best I could find was this:
    Sounds like H.265 is MUCH slower. The author said a 10 second video took anywhere from 9 to 35 seconds to compress a frame. It sounds like if you're willing to sacrifice the file-saving benefits of H.265, you can stick to H.264. Otherwise I think you just get to sit and wait.
  5. joema2 macrumors 68000


    Sep 3, 2013
    Your 2015 iMac is probably using all available and necessary hardware resources. High CPU or GPU levels do not always reflect efficient use of hardware. See below tests I just ran.

    Also the CPU's Quick Sync activity may not be picked up by iStat Menus. Quick Sync is a separate logic block mostly unrelated to the on-chip GPU or CPU cores. I don't know if Quick Sync activity is visible to any monitoring software.

    HEVC/H265 is extremely compute-intensive, far more than H264. If not handled at least partially by hardware acceleration, encoding this is mind-numbingly slow, even on a 10-core iMac Pro.

    Your 2015 iMac has a Sky Lake CPU which has less extensive HEVC support than Kaby Lake. The 2017 iMac uses a Kaby Lake CPU which on my FCPX tests is about 2x faster than the 2015 model at encode/decode of H264. I assume it's also faster at HEVC/H265 but I haven't done back-to-back tests of that. Quick Sync differences between Sky Lake vs Kaby Lake :

    I did the below encoding tests on my top-spec 2017 iMac 27 using FCPX 10.4 and macOS 10.13.4. Media is a 30 second 4k H264 8-bit 4:2:0 clip from a Sony A7RIII.

    FCPX export to 4k H264, single-pass: 00:23 (CPU level = low)
    Premiere Pro CC 2017.1.2, single-pass: 1:16 (CPU level = high)

    FCPX export to 4k H264, multi-pass: 00:37 (CPU level = low)
    Premiere Pro CC 2017.1.2, multi-pass: 2:34 (CPU level = high)

    FCPX export to 4k HEVC 8-bit: 1:04 (CPU level = low)
    Premiere Pro CC 2017.1.2: 2:21 (CPU level = high)

    So you can see Premiere has very high CPU levels but it doesn't equate to best encoding performance. It is not using Quick Sync efficiently, so burns a lot of CPU cycles. The CPU meters are pegged but the actual rate of work is slow. By contrast, FCPX has low CPU levels in these tests but encoding performance is much better. Much of the work is done by Quick Sync and that's not reflected in any performance graph.

    You can cross-check your performance by taking a 30 sec 4k H264 clip and encoding that to 8-bit HEVC in FCPX and comparing it to my above times. That will indicate whether and how much difference exists between the 2015 and 2017 iMac for HEVC encoding.

    IF there's a major difference (say, 2x) you can get a 2017 iMac, or you could try encoding to H264 instead. HEVC is incredibly difficult to handle, especially in large batches. You shouldn't expect encoding or transcoding HEVC/H265 to be fast on anything except special transcoding hardware:
  6. adamjackson thread starter macrumors 68000

    Jul 9, 2008
    @joema2 - Very helpful! I've definitely noticed since shooting on a Hero6 + iPhone 8 which both default to HEVC in 4K @ 60FPS, my workflow has slowed down considerably from Import to Editing. Transcoding just feels extremely bottle-necked even though this was the fastest late-2015 iMac you could get. I don't make money on my video work....well $350 a month on YouTube so an iMac Pro isn't justified financially. I guess I have two choices, stop shooting HEVC or buy a faster machine :p

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