Very slow rendering in Final Cut Pro X? A workaround
In the past couple of years of using Final Cut Pro I’ve had few problems in rendering timelines in Final Cut Pro X, but have seen reports of other people facing this issue.
Yesterday I wanted to compare the speed of an old MacBook Pro with my slightly less old iMac. I set up a timeline with one title generator and timed them both.
Mid-2011 27″ iMac 2.5 GHz Core i7 – 23.5 seconds
Mid-2009 17″ MacBook Pro 2.8 GHz Core Duo – 1 hour 19 minutes 15 seconds
Clearly something was up. Although the iMac has every possible advantage over the MacBook, this kind of difference looks like a bug. The most likely culprit is having a lower powered GPU with not enough memory.
It shows that if you do have access to a faster Mac, it is worth moving a problem project to a higher spec system. The speed difference may be orders of magnitude higher than you expect.
If you don’t have access to a faster computer…
Final Cut Pro W
The W is for ‘Workaround.’ Here’s another workaround to add to an already long list…
Seeing that the rendering got very much slower after the render was 30% done, I guessed that there is a programming problem. I tried an alternative way rendering in Final Cut Pro. If it started to slow down, I quit the application. I then restarted Final Cut and started the render again:
1. I timed the render until 36%, when it started to slow down.
2. I stopped the render (using Command-.) and quit Final Cut
3. I started a new render (which always start at 0%), timed it until it reached 36% again
4. I stopped the render (using Command-.) and quit Final Cut
5. I started a new render, timed it until it reached 50%
6. I stopped the render (using Command-.) and quit Final Cut
7. I timed one more render until it finished.
The render time – not including the quitting and restarting of Final Cut Pro – reduced from 1 hour 19 minutes to 2 minutes 20 seconds.
What about exporting movies?
This workaround may be useful while editing to get out of a big rendering problem, but doesn’t directly help when sharing Quicktime movies. Unlike Final Cut Pro 7, X doesn’t use rendered frames when generating Quicktime movies. Usually this is good news as X is faster when outputting movies than when it renders timelines. In the case of a clip, generator, or plugin causing Final Cut to slow down an unfeasible amount, export becomes a problem.
The workaround in this case is to export your timeline as a series of movies (quitting and restarting Final Cut before each export), reimporting them and joining them together in a new project!
This method took 2 minutes 55 seconds of rendering – not including restarting the app three times or exporting the combined movie, but better than waiting over an hour!
Now to report this bug to Apple…
alex4D old blog 
Alex,
I have seen a similar phenomena on a fairly hefty Pro with a powerful GPU. I think what was happening was that there were enough other big applications running, specifically Photoshop with 30 open pictures, that the file swapping code in ML4 got confused.
I cleared it with a variation on your workaround which was to shut everything down and reboot.
I have seen similar behavior in FCP7, which was fixed the same way. Sometimes with 7, it seemed to make a difference if FCP was started first, before the other aps.
Best, Dave
> >
I am sure that is not a problem of CPU power but of the RAM management of FCPX and the different Macs. I have found a way out of the problem in a the forum of the Apple Community.
Quit FCPX. Open up Terminal and copy/paste the following:
defaults write com.apple.FinalCut OZPreferenceManager::CachePercentage -int 20
It stops FCPX from taking the entire RAM of the Mac. That small line increased the performance of my computers dramatically. For those who do not want to use Terminal I have made a small application in Automator. Just ask and I will send it to you.
All best, Detlev
That would make sense. There’s a copy of Motion built into Final Cut Pro, but you can’t set its memory cache preferences.
I tried the command, restarted my Mac and unfortunately the render is currently at 67% with 21 minutes elapsed…
Hi Alex.
Try it again, but do not restart the Mac
Hi Detlev, that helped. Question how do I change it back after I enter the above in terminal? Is the “-int 20” changing it to 20 percent cache? Thanks
Detlev, no difference after entering the prefs command and then running Final Cut: render is at 67% after 21 minutes. The render usually goes more and more slowly – ending up taking over an hour. Oh well!
It sounds like a corrupt file. Or a picture far to big. Give Final Cut a chance. Rerender the video to ProRes and reduce the size of pictures. And the last chance is to render the difficult piece of pictures in Motion and export it as ProRes.
I have seen one more solution. Another Final Cut user divided his project into several compound clips and was very successful with that. With this method he was able to reduce the render time.
By the way: 67 % is very strange for me. On each of my computers the exporting of the video in FCPX is finished after 50 %. Then it jumps up to 100 %.
Detlev
I’m not exporting. I’m rendering the default copy of a single FCP Title: ‘Far Far Away’ – which has a duration of only 10 seconds. Rendering in this case goes up to 100%.
No corrupted large images, just lots of information going through the registers and memory of the GPU.
I have learned that FCPX does not make use of render files. But that it is much faster in exporting (witzour the render files). So try to make a range around your title compositing and export it. It should be faster.
Detlev
Detlev,
I covered this in my post: that exporting doesn’t include render files, that exporting is usually faster, and that you might need to export ranges.
Thanks though!
You do awesome work, Alex! Please let us know when Apple acknowledges your research, identifies their code problems, and then fixes them.
Nice work! If this is indeed due to a bug or simply poor code within FCP, it’s a major problem, and one that there is really no excuse for in any professional application. Do you have an idea of how it could be fixed by Apple?
Hey Alex:
Any updates on this? Very interested.
The 10.0.9 update still bogs down on my MacBook Pro. It just happens a little later – at 40% instead of just over 30%.
Oh well.
Same problem running Final Cut X 10.0.9 3.6 Core i5 with extra ram almost want to go back to Final Cut 7 seems like almost the same rendering time.