Problem with RAM preview of fractal noise

I've got a fairly simple comp containing only five layers. The top four are embedded comps, with the bottom layer being a plane with an animated fractal noise effect.  If I hide the top layers and leave only the plane visible so I can test my fractal noise settings, the RAM preview doesn't behave properly.  It appears to make the preview all right, but playing it back isn't smooth at all.  It's just as stuttery as the un-previewed parts of the comp.  However, once I un-hide even one of the other comp layers above it and RAM preview again, the preview plays back smoothly.  Has anyone encountered this before?  I've done plenty of tests with animated fractal noise layers, and I don't recall ever having this problem playing back a RAM preview of one.

This is happening in HitFilm Express 2017 version 5.0.0121 (Update 7) running on a Mac Mini, OS X Yosemite, 8GB RAM.

If anyone wants to test this, I'm using the Fluid fractal noise type, all default settings, except I have the Seed keyframed to go from 4500 to 4502 over 8 seconds.  I tried changing to other fractal noise types, and while some of them had less lag than others, they all weren't perfectly smooth unless one of the upper layers was also visible when generating the RAM preview.  I even copied that plane layer into a brand new comp all by itself, but it exhibited the same behavior.  However, once I added a grade layer above it, its RAM preview played smoothly.


  • Very weird. Not had that, but do have performance problems just playing a RAM Preview clip in a loop. When it loops, it skips the first 1/4 to 1/3 of a second, even though the performance overhead of simply moving the playhead back to the beginning should be negligible. 

    Does yours stutter even on the first playing, or when looping? Or is it always bad, then worse when looping?

    Yours sounds like something worth reporting. I have reported my findings.

  • edited September 2017

    In my earlier tests I was only making a RAM preview of a small portion of the comp just to check the speed of the fractal noise movement, and I wasn't looping playback of the previewed area.  I just tested it again with the full comp length previewed.  It stutters from the very start of playback, and doesn't seem to change when looping.

  • You did not mention the rez so I just did HD 1080 29.97.

    In a quick test it looks like the fractal noise is still computing even after a ram preview and playing the ram preview. On my machine Window, 4Ghz 4770k, GTX 980 the fractal noise will play real time without ram preview. Fractal noise is compute heavy and the GPU utilization is pegged to the wall (97). When playing a ram preview I would expect the GPU use to drop to near nothing as it is while playing anything else. In this test it does not and the GPU compute stays the same as without ram preview. It is as though the fractal noise compute is not respecting the ram preview and is always done.

    I'll play some more but just reporting a quick observation for now.

  • One additional test confirmation. Putting a video clip above the fractal noise at 50% opacity and doing the ram preview I just what I expect. Playing after building a ram preview has GPU utilization drop to a few percent when playing ram preview.

    So it seems that a standalone fractal noise effect on a plane does not respect the ram preview function.

  • Nice detective work. :)

  • Ditto!  I hadn't thought to look at GPU usage, but after installing a better resource monitor than the default one on my Mac, I see pretty much the same thing you reported, Norman, though on mine the GPU usage during RAM preview playback of nothing but fractal noise is about half of what it was during the creation of the preview.  Still, it shouldn't even be that high.

  • edited September 2017

    I also tried two fractal noise planes in the comp and ram preview is still not respected. So it does not seem to be a single layer with fractal noise but just fractal noise itself so long as nothing else like normal media exists in the comp. Well, all I've tried is a simple media file (AVC in MP4) on top of the fractal planes. I'll let FxHome worry about all permutations. Where there is one thing that does not respect ram preview there can be others.

  • As I mentioned in my original post, simply adding a grade layer is sufficient to fix the problem.

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