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FCP X sluggish with XAVC 4K

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Brett Sherman
FCP X sluggish with XAVC 4K
on Mar 1, 2018 at 1:14:52 pm

One of my main bottlenecks is how sluggish FCP X handles some Sony formats. Namely on the A6500 and A7SII. I shoot 4K 30P 100kbps on these cameras. Playing back in FCP X is really sluggish. The same is not true of the C200 MP4 150kbps, so clearly it is capable of decoding H.264 4K material efficiently. There's just something about the Sony codec that it doesn't like. Any ideas (besides transcoding everything)?

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Brett Sherman
One Man Band (If it's video related I'll do it!)
I work for an institution that probably does not want to be associated with my babblings here.


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Joe Marler
Re: FCP X sluggish with XAVC 4K
on Mar 1, 2018 at 3:32:51 pm

Both FCPX and Premiere CC can be sluggish on many different 4k H264 codecs, even on fairly high-end hardware.

If you are on a 2013 Mac Pro which does not have Quick Sync or any other encode/decode acceleration, in general H264 editing or transcoding will be quite sluggish. It might even be slower than a 2015 MacBook Pro.

I haven't tested C200 material, but all 8-bit XAVC 4k from the A6300, A6500, A7R2 and A7R3 is similar. Likewise 8-bit 4k H264 material from our Panasonic DVX-200 and GH5 is also similar, also from our DJI Inspire 2 drone. So it's not unique to Sony or the XAVC-S variant of H264.

The fastest machine I've tested on 4k H264 editing response in FCPX is the 2017 i7 iMac. It is about 2x faster than the equivalent 2015 model, about 2x faster than a 12-core D700 Mac Pro. Those are rough approximations based on decoding and creating optimized media or encoding from ProRes to 4k H264 output.

Harder to measure is editing smoothness in the timeline. But the 2017 iMac is much smoother on 4k H264 than the 2015 or earlier iMac.

The 10-core Vega 64 iMac Pro is not dramatically faster on 4k H264 than the 2017 iMac in most cases and even slower in a few scenarios, although faster than the 2013 Mac Pro. This is apparently because Xeon doesn't have Quick Sync and Apple is using AMD's UVD/VCE hardware instead. It's faster than software decoding but (at least in FCPX 10.4) it's not as fast as Quick Sync. Hopefully this can be optimized in future versions: https://en.wikipedia.org/wiki/Unified_Video_Decoder

There are many different encoding parameters for H264: bit rate, frame rate, bit depth, chroma sampling, GOP size, GOP pattern, I or P frame interval, etc. This article shows how many variations there are: http://www.tiliam.com/Blog/2015/07/06/effective-use-long-gop-video-codecs

Some of these can be examined with tools like MediaInfo but it doesn't reveal this for all variants. The XAVC-S material is all *inter*-frame; I don't know about the C200's 150 mbps internal 4k codec.

You can also have *intra* frame H264 encoding which is typically much quicker to decode. E.g, the 4k intra-frame 300 mbps material from a Canon XC15 is very smooth to edit. If the C200 codec is intra-frame that could explain why it's so much smoother, but at 150 mbps I suspect it's inter-frame just like Sony's XAVC-S.

On my 2017 top-spec iMac, a single stream of XAVC-S 4k h264 is fairly quick in FCPX 10.3.4. By "quick" I mean 1x playback never drops frames, JKL lag is fairly low, fast forward and reverse playback is usable though not perfectly smooth. The 10-core Vega 64 iMac Pro running 10.4 is roughly the same, maybe slightly more laggy. On my 2015 top-spec iMac it's much more laggy.

Multicam requires proxies or optimized media, even on a 2017 iMac or iMac Pro. This is for XAVC-S or most other 4k H264 interframe material I've tested. This isn't unique to FCPX -- Premiere CC is worse (on Macs) as it apparently doesn't use Quick Sync acceleration. Supposedly starting in 2016 Premiere (on Windows) started using Quick Sync, five years after it was released with Sandy Bridge CPUs.


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Brett Sherman
Re: FCP X sluggish with XAVC 4K
on Mar 1, 2018 at 10:31:13 pm
Last Edited By Brett Sherman on Mar 1, 2018 at 10:34:06 pm

[Joe Marler] "Some of these can be examined with tools like MediaInfo but it doesn't reveal this for all variants. The XAVC-S material is all *inter*-frame; I don't know about the C200's 150 mbps internal 4k codec."

Any 150 mpbs 4K has to be inter-frame. I'm sure it has a slightly different H.264 implementation than XAVC 4K. But not that would explain the massive performance difference between the two formats. Quicktime doesn't like it either. There seems to be something in particular that the Mac doesn't like about it.

--------------------------
Brett Sherman
One Man Band (If it's video related I'll do it!)
I work for an institution that probably does not want to be associated with my babblings here.


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Joe Marler
Re: FCP X sluggish with XAVC 4K
on Mar 1, 2018 at 11:07:52 pm

[Brett Sherman] "Any 150 mpbs 4K has to be inter-frame. I'm sure it has a slightly different H.264 implementation than XAVC 4K. But not that would explain the massive performance difference between the two formats."

If you could point me to about 5 sec of that material I'd be happy to test it on FCPX and Premiere on both iMac Pro and 2017 iMac.


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