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14 Nov 2020
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TOPIC: Pre rendering files on timeline has no effect

Pre rendering files on timeline has no effect 06 Oct 2020 13:57 #110366

  • tomasz.derlacki
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I'm having an issue with the render function. After adding effects etc I used to be able to select and pre render chosen clips so I could play them back smoothly on the time line. This is not working. I can render the whole time line and this has no effect. Some clips will always take 2 extra seconds to display regardless if the effects are on or off. Have you got any suggestions on how to fix this. I have re installed fcpx and I have the latest version now.

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Pre rendering files on timeline has no effect 07 Oct 2020 11:18 #110387

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I just noticed this for the first time ever. I think 10.4.10 introduced a bug here.

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Pre rendering files on timeline has no effect 07 Oct 2020 12:30 #110389

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tomasz.derlacki wrote: ....After adding effects etc I used to be able to select and pre render chosen clips so I could play them back smoothly on the time line. This is not working...


In general it should work, but there have long been problems with FCPX properly using render files. In some cases it produces render files then won't use them. In other cases it loses render files when no edits are made or when simply toggling between proxy and orig. media mode (when both have valid render files) or when re-launching FCPX. In certain cases you can render the timeline, it won't use the render files, then you re-launch FCPX, render timeline again and it will use them. In yet other cases you render the timeline and the render dots stay present. This seems partially related to which effects are used and the order in the effects stack. There is a group of "poorly behaved" built-in effects which apparently trigger this, but the underlying problem is likely broader.

The problem is severe when using a compute-intensive effect such as Neat Video and a poorly-behaved built-in effect in the stack prevents re-use of those render files for export. In those cases the export time may suddenly increase by a factor of 50, despite the timeline being fully rendered.

There is yet another case for "fast path" export whereby if the timeline, render format and export format are all ProRes 422, it's supposed to simply grab the render files and write to output without any encoding. For unknown reasons it sometimes fails to do this.

So in general there are two broad cases: (1) Do existing render files speed up timeline operations, and (2) Do existing render files speed up export. In some cases the render files will speed up timeline operations but FCPX fails to use them for export. Within those broad categories there are many sub-cases involving exact circumstances of render file durability, and whether they are used.

I've had multiple long conversations with Apple Pro Apps escalation support, both verbally and in writing on this. For some of those Apple Engineering was being consulted during the call. They refuse to admit it's a problem, so I basically gave up for now. I provided them in writing a very easy, concise replication scenario, so there is no question of misunderstanding or ambiguity. This situation apparently requires escalation to the product management level.

It's possible there is yet a new issue on 10.4.10, but so far I haven't seen it. I just noticed if a built-in "Basic Lower Third" title is placed over a clip with Neat Video, even with no other 3rd party or built-in effects, the render files will be used for timeline operations but not for export. IOW during export FCPX will re-compute all clips with Neat Video, even if valid render files exist.

www.fcp.co/forum/4-final-cut-pro-x-fcpx/...roject-switch#104227

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Pre rendering files on timeline has no effect 09 Oct 2020 18:36 #110412

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I have an open case with Apple Support now to address this very issue. Mine originated with the fact that the timeline always shows a need to re-render each time you re-open the project after a close even though the project was completely rendered before closing. This was demonstrated to Apple Engineering with only standard Apple titles, generators and SFX. It was easily recreatable.

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Pre rendering files on timeline has no effect 09 Oct 2020 18:53 #110413

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Could you give the steps to reproduce this? Thanks.

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Pre rendering files on timeline has no effect 09 Oct 2020 19:05 #110414

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I don't really pay attention to the time it takes to do the final render but the more to the performance of the timeline. I want to watch the footage with added effects and transitions to gauge the flow but then hit some snags on certain clips and transitions. Pre rendering them makes no difference at all to how they perform on the timeline. I have tried deleting rendered files and re rendering with no effect. Re installed fcp but that did not help.

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Pre rendering files on timeline has no effect 09 Oct 2020 22:50 #110417

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Tom Wolsky wrote: Could you give the steps to reproduce this? Thanks.


There are various manifestations of this but one of the simplest scenarios is below. I discussed this at length with Pro Apps Escalation Support, who after discussing it with Apple Engineering said any alleged use of render files to accelerate export was undocumented and a bug could not be filed.

I reminded them various aspects of this behavior have already been published, such as the article by Peter Wiggins: www.fcp.co/final-cut-pro/tutorials/2177-...-speed-up-the-export

They said this doesn't matter, there is no documented behavior that render files accelerate export, therefor there is nothing to fix or improve.

- Import a 60 sec 4k ProRes 422 clip
- Add Color Wheel effect and make any adjustment. Render dots appear.
- Do timed export to 4k ProRes 422 on a fast SSD (at least 900 MB/sec). On my 10-core Vega 64 iMac Pro, this takes about 22 sec
- Render timeline using CTRL+R. Render dots vanish.
- Repeat above export. On my machine the export time diminishes from 22 sec to 6.9 sec, or about 3x faster. This is 100% reproducible. The more compute-intensive the effect, the greater the *export* performance benefit of pre-rendering the timeline.

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Pre rendering files on timeline has no effect 10 Oct 2020 00:14 #110418

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Thanks joema. And this is now broken in 4.10? I can’t test it with 4.8 unfortunately.

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Last edit: by Tom Wolsky.

Pre rendering files on timeline has no effect 10 Oct 2020 00:49 #110419

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Tom Wolsky wrote: Thanks joema. And this is now broken in 4.10? I can’t test it with 4.8 unfortunately.


No, it's been this way quite a while. I tested each version since 10.4.6 and it happens on all of them. I don't know how far back the behavior goes.

To be clear -- the specific scenario I posted above is not a bug -- it simply illustrates the "fast path" optimization for exporting a fully-rendered ProRes 422 timeline to ProRes 422 output, vs a non-rendered timeline. The significance is Apple strongly claimed there was no such optimization and even if it existed it's undocumented, therefore no related behavior is subject to an improvement request. IOW if sometimes an export is 5x slower due to failure to use render files, Apple doesn't accept that as a bug.

I simply used this scenario because it's the simplest I could think of. Below is a slightly more complex one that is a true bug, and happens on all versions I tested since 10.4.6. Maybe it existed before then. For testing purposes, background render is disabled in all these cases.

- Import a ProRes 422 test file
- Adjust color with color wheels
- Add the built-in Aged Paper effect
- Do a timed export to ProRes 422
- Render timeline with CTRL+R; note render dots vanish
- Do timed export to ProRes 422 -- it is no faster; fails to use render files for export.
- Re-launch FCPX. Note render dots are back -- it lost the files. That is 100% reproducible on the first re-launch.
- Render timeline again with CTRL+R; render dots vanish
- Do timed export to ProRes 422 -- it is now much faster. THIS time it uses the render files.

Above is one small example. There are many variations of this. In a severe situation it can unpredictably cause render or export performance to become 50x slower.

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Last edit: by joema.

Pre rendering files on timeline has no effect 10 Oct 2020 01:11 #110420

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Thanks again. Presumably Apple acknowledges the problem of the lost render files, which has never been dealt with.

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Pre rendering files on timeline has no effect 10 Oct 2020 01:33 #110421

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Tom Wolsky wrote: Thanks again. Presumably Apple acknowledges the problem of the lost render files, which has never been dealt with.


I'm not sure of that. I should probably open another support case to discuss that with them, maybe I'll have more success this time.

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