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14 Nov 2020
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TOPIC: Forever rendering and lag.

Forever rendering and lag. 30 Nov 2020 21:38 #111133

So ever since I purchased my iMac Pro, I've always had an issue with lag during mulitcam cutting.  It's always choppy.  My iMac Pro has 64 gb of memory, a Radeon Pro Vega 64 with 16gb of ram, and my processor is 3.2ghz 8-core Intel Xeon W.  

I run editing off SSD drives with over 900 mbs transfer rate.  The choppy problem is from project to project, no matter what I do.  I've been through 5 Apple techs and they've run out of ideas.  My personal opinion is this massive machine is designed wrong, maybe wrong video drivers for FCPX.  

Here is a screen recording of the type of lag I get.  The video there is 60p 4k, 4 30p from a gopro and 60i from a Canon xf 300.  All supported cameras according to Apple. 


For the life of me I can't imagine any professional studio going through what I go through.  When it is laggy, my machine is only using 5% or so of my CPU Resources.  

I'm lost. 

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Forever rendering and lag. 30 Nov 2020 22:30 #111134

Have you optimised the go pro footage? I think every computer will have problems playing back non optimised (basically transcoded to ProRes). footage in a Multicam.
Just a guess as I don't do multi cams w GoPro footage.

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Forever rendering and lag. 01 Dec 2020 00:05 #111139

Maybe under "View" switch to "Better Performance". Personally I've made it a rule to transcode any H.264 footage, GoPro, AVCHD, etc to ProRes. Like cofe recommended, optimized. I also have never edited multicam, but I was getting some lagging since updating to 10.5 (also on a current jazzed up iMac w/external RAID) even using ProRes footage. I switched to Better Performance and all was right. Maybe it's partially a 10.5 thing. I'm also still on Catalina.

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Forever rendering and lag. 01 Dec 2020 10:50 #111147

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Cosmichrist wrote: ...When it is laggy, my machine is only using 5% or so of my CPU Resources.... 


That is possibly because it's bottlenecked on hardware-accelerated video decode. Whether done by Intel's QuickSync or (in your case) Apple's T2 chip, there is no monitoring program which shows this. You have to infer the operation by noting all other performance counters are low.

Past generations of video acceleration may handle some new codecs poorly. This includes some 10-bit 4:2:2 codecs, especially HEVC (aka H.265). GoPro and DJI often use that, don't know about the C200.

Step one is play a clip from each camera in Quicktime Player and do CMD+I. That will show the codec specifics, including bit depth, data rate and chroma sampling.

However there are no render dots above the timeline which indicates it should be fully rendered. Normally that makes playback smooth. As a test disable background rendering in FCP preferences, delete all render files with File>Delete Generated Library Files>Delete Render Files>All. Then as needed do manual renders of the timeline with CMD+A to select all clips and CTRL+R to render. In some cases FCP can lose track of existing render files.

Make sure you have installed the latest version of Apple Pro Video Formats. On Mojave and later, this is done in System Preferences>Software Updates. In some cases it can make a significant performance difference. 

However it's likely your solution will be transcode that material to either optimized or proxy media. Select all clips in the event browser with CMD+A, right-click and pick transcode. As a rule of thumb, 50% ProRes proxies are about 60% the size of H264 originals and optimized media is about 5x the size of H264 originals. For optimized media, FCP will automatically use that. For proxies you set the viewer to "view proxies".

If you have mixed 4k and 1080p material, proxies may only be needed on the 4k clips. In that case you can only generate proxies on that and (as of 10.4.9) use the new "View>Proxy Preferred" feature. That uses only the proxies you generated and retains full-res display of the 1080p clips.

Make sure you are not running the Chrome browser which can negatively impact the MacOS VideoToolBox framework. Also if you're using any wireless audio monitoring, as a test temporarily disable Bluetooth on that machine. In a few cases it may cause odd or laggy behavior.

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Last edit: by joema.

Forever rendering and lag. 03 Dec 2020 15:36 #111211

Thank you so much.  You're right about he Chrome browser.  I found that nugget on an internet search.  None of the techs at Apple have heard of it. But I just uninstalled Chrome to avoid that issue.  

I've been through five advisors with Apple, and it's unfortunate that I seem to know more about video editing than a few of them. 

The latest I got was that my issue with my footage is that I didn't capture each disk from the camera, instead I copied all my footage over then imported from a hard drive.  I feel like Apple has no idea what to do and keeps telling the the same thing. 

I have an Apple appointment so they can put hands on my machine, I hope to test my footage/drive with one or two of their other machines.  Either way, I've lost so much time with a machine that should not have these problems.  

Thanks for listening.  

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Last edit: by Cosmichrist.

Forever rendering and lag. 03 Dec 2020 16:34 #111214

I already pay for Premier,  I think I'm going to shove the same multicam project into Premier and see what happens.    

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Forever rendering and lag. 03 Dec 2020 17:36 #111215

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Please post your results. Be sure to test scrubbing forward/backward on the timeline using JKL keys. Set Premiere to 1/4 resolution which reasonable for editing. Enable the multicam viewer.

If you did not use proxies or optimized media on FCP, don't use that on Premiere. If you used proxies or optimized media on FCP, use that on Premiere.

When using JKL, watch carefully after pressing the L key three times to fast forward, then press the J key three times to reverse at the same speed. Compare how many frames per sec the viewer is updating on each NLE. Look for any major response lag to JKL and for any major frame lags on the viewer, such as it not updating for a 1-2 seconds after reversing directions.

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Forever rendering and lag. 03 Dec 2020 17:51 #111216

Thank you.  I will post when I get results.  My main hope is that I can actually play the multicam in Premiere.  It's so bad in FCPX, it's impossible to play and cut.   Thank you again.  

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