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25 Jan 2021
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Transcoding is slow but FCP is taking very little CPU time 22 Jul 2021 23:33 #115516

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I've got a bunch of GoPro an Canon video files on an external HD. I'm running Mac OS 11.3.

They seem to be transcoding very slowly, or at least slower than what I've come to expect.

I understand that this could just be me being impatient but I'm wondering if there is a problem because both FCP and VTDecoderPCService are very low, FCP is 15-20%.

I'd like the transcoding task to use my entire computer since I'm not doing anything else on it, other than posting this of course :) . So is there anyway to get FCP to allocate more resources or is what I'm seeing normal?

Thanks for any help!

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Transcoding is slow but FCP is taking very little CPU time 23 Jul 2021 00:25 #115517

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....a bunch of GoPro an Canon video files on an external HD. I'm running Mac OS 11.3. They seem to be transcoding very slowly, or at least slower than what I've come to expect.

I understand that this could just be me being impatient but I'm wondering if there is a problem because both FCP and VTDecoderPCService are very low, FCP is 15-20%...

What year, model and config of Mac? What version of FCP? What type of external hard drive? Transcoding to what codec?

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Transcoding is slow but FCP is taking very little CPU time 23 Jul 2021 02:34 #115518

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....a bunch of GoPro an Canon video files on an external HD. I'm running Mac OS 11.3. They seem to be transcoding very slowly, or at least slower than what I've come to expect.

I understand that this could just be me being impatient but I'm wondering if there is a problem because both FCP and VTDecoderPCService are very low, FCP is 15-20%...

What year, model and config of Mac? What version of FCP? What type of external hard drive? Transcoding to what codec?

Not sure that how that makes any difference since the point is that FCP is using very little CPU time. If there is no way to get FCP to use more resources then the configuration doesn't matter.

However the Mac is an iMac iMac (Retina 5K, 27-inch, 2020) 3.8GHz 8-core Intel Core i7 65GB 2667MHz DDR4 AMD Radeon Pro 5700 XT 16GB

10TB WD HD

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Transcoding is slow but FCP is taking very little CPU time 23 Jul 2021 03:11 #115519

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...Not sure that how that makes any difference since the point is that FCP is using very little CPU time. If there is no way to get FCP to use more resources then the configuration doesn't matter.

However the Mac is an iMac iMac (Retina 5K, 27-inch, 2020) 3.8GHz 8-core Intel Core i7 65GB 2667MHz DDR4 AMD Radeon Pro 5700 XT 16GB

10TB WD HD

In general for this case you want CPU to be low. The FCP software code path is likely calling the VideoToolBox framework which in turn is using Intel's Quick Sync decode/encode hardware. That usually doesn't show up on in Activity Monitor, as it's "fixed function" hardware. IOW it's not CPU, it's not GPU, but specific circuitry to decode and encode certain Long GOP codecs.

If you want to see high CPU, do the same task in Premiere Pro. The CPU cores will be pegged at the max, fans will be loud, and it is much slower. If Quick Sync was discretely instrumented and the performance counters were revealed by Activity Monitor you could see that, but it's not and you can't.

If the export codec is ProRes or 4:2:0 H264 or 8-bit HEVC, it is normally fairly fast, e.g, roughly real time for 4k conversions. If the export codec is 10-bit HEVC it is extremely slow on x86 Macs, but fast on Apple Silicon Macs. That is caused by limitations in Intel's video acceleration hardware.

To illustrate how critical the exact year and model of Mac, in my tests FCP on the 2017 iMac 27 using Intel's "Kaby Lake" CPU is 200% faster than the 2015 iMac 27 using the "Skylake" CPU -- simply because Quick Sync was improved between those two CPU versions. The 2015 4-core iMac 27 was in turn about 200% faster than a 12-core D700 Mac Pro on the same H264 transcode task, simply because the Mac Pro didn't have Quick Sync.

Since you didn't state what export codec you're using it's hard to tell. If you are transcoding to ProRes 422, it is mostly a decode problem. If you are transcoding to 8-bit 4:2:0 H264 or HEVC, FCP must handle both decode and encode, and the specific acceleration hardware is the bottleneck, but it's generally about 5x faster than a software-only code path. If you are transcoding to 10-bit HEVC, the current Intel Quick Sync hardware evidently doesn't support that and it will be very slow (but CPU cores will all be very high).

If you could state the transcode speed, that would help. IOW for 60 sec of 4k/30 material, how long does transcoding that take? If the material is 60 fps or 120 fps, state that -- it requires transcoding 2x or 4x the frames per second as 30 fps.

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