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Render files disappearing

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chris walker
Render files disappearing
on May 20, 2017 at 6:16:05 pm

I had asked earlier how to speed up the final export of a project, using an underpowered computer, when using proxies to edit 4k material on a 1080p timeline. One solution was to periodically switch the view to optimized/original and render out already edited portions so that less transcoding has to be done upon final export. The problem with that, though, is that many of my render files keep disappearing! For example I just rendered out a five minute section, it was definitely fully rendered, playing back smoothly and with no orange line indicating rendering was needed. Then, without doing any further editing of any time, I shut down fcpx. When I opened it up again, some of the shots I had just rendered had the orange line again, indicating a render is needed! And they did in fact need re-rendering. Why is this? What can I do about it? I thought maybe if I rendered a shot that was covering up a clip on the main storyline, for some reason that would require a re-render if I shut down and started again, so I tried the render with all the shots being on the main storyline. Same problem, some renders remain and others disappear.
I would greatly appreciate some help with this. If I can't get these renders to remain my final export can take 48 hours or more.


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Noah Kadner
Re: Render files disappearing
on May 20, 2017 at 7:42:08 pm

rendering bits of the timeline in general doesn't really save you much in the long run. What saves you much over the long run is optimizing everything that's in a project to proxy or optimized media

Noah

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Joe Marler
Re: Render files disappearing
on May 20, 2017 at 9:00:01 pm

[chris walker] "I had asked earlier how to speed up the final export of a project, using an underpowered computer, when using proxies to edit 4k material on a 1080p timeline. "

For reference, that was this thread: https://forums.creativecow.net/thread/344/46986#46991

[chris walker] "One solution was to periodically switch the view to optimized/original and render out already edited portions so that less transcoding has to be done upon final export. The problem with that, though, is that many of my render files keep disappearing!"

By "render out" you mean render the timeline section with CTRL-R. What you describe is not the render files disappearing (although it looks like that) but they have been invalidated by some operation or action. The render files are a cache of rendered timeline content. Like any cache they can be invalidated by various events. This can be related to certain effect, but FCPX's decision to re-render is not under control of the effect code. IOW FCPX is responsible for data integrity and it decides the render cache no longer accurately represents the timeline and must be rebuilt. It is very common to see cases where some seemingly innocuous action causes the render bar to go orange. It's conceivable some of these might be over-conservatism on the part of FCPX and maybe given further algorithmic refinement it could be improved, but that is only speculation.

On my machine the render cache is not invalidated by restarting FCPX -- for straight video with no effects, or just built-in color correction. But adding stabilization then rendering the timeline, then restarting FCPX will invalidate the cache necessitating a re-render. I don't know why that is. Nothing changed on the timeline. Maybe they are using some in-memory cache for certain effects that is not backed by disk storage.

I understand your situation but I don't think you can totally rely on the render cache being 100% predictable. From my previous tests it seems that exporting 4k H264 content from a 1080p timeline to 1080p H264 was about 25% faster than exporting to 1080p ProRes, at least on my 2015 iMac 27. Of course if you are facing a 48 hour export that might not be sufficient even if H264 was acceptable.

I recollect you were exporting 80 min. of 4k material from a 1080p timeline to 1080p ProRes. Are you saying without the render cache, that takes 48 hours? My 2015 iMac 27 would take about 33 minutes to do that, which implies it's not your machine but possibly computationally-intensive effects on that timeline. E.g, if I used stabilization, Neat Video and Digital Anarchy's Flicker Free on 80 min. of 4k it might also take 48 hr.

Is it possible you can do a test export with all effects removed to see what % of the problem is from effects vs the basic video? Starting with 10.3.x, there is a new feature to remove all effects from all clips. So you can duplicate the project, then remove all effects from the duplicate then add them back selectively: 

https://support.apple.com/kb/PH12615?locale=en_US

You previously indicated that using 80 min of 1080p content the export time was "reasonable". I'd expect 4k to be at least 4x your previous export time -- if all other conditions were maintained constant. It's conceivable some effect is having a non-linear performance degradation at the higher resolution. You'll have to test this to isolate it.


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