Weird cache bug with adjustment layer

Hi everyone. I often use adjustment layers to apply motion blur (Fusion optical flow + vector motion blur) or other third-party plugins. The problem is that when I close and reopen the project, sometimes the animation or motion blur gets messed up—some frames freeze or show a frame from a completely different clip. Restarting Davinci doesn’t help because it seems to remember the cache error. The only fixes are duplicating the adjustment layer and then deleting the duplicate (which somehow fixes the original) or completely clearing the cache. You can see the issue in the video.

Any ideas what could be causing this?

Davinci Studio 19.1.4
MacOS Sequoia 15.3.2

Since adjustment layers essentially work with a composite image of what is bellow it, not actual clips themselves, I would imagine the adjustments are applied to the composite image that gets cashed for each frame as you play.

Some effects, especially in fusion which are not just something on top that is easy on processing, but require access to actual files, and are heavy on the processor will likely glitch unless they are pre-rendered and backed in.

Similar behavior happens when you use „Background “as media source in fusion. Option in the MediaIn node. Its a composite image from edit page and it’s cashed each frame. When scrubbing or processing faster than it can cache, it starts to glitch. And some effects like IntelliTracker do not work at all, because they require access to whole clip. Similar thing happens when you load audio in fusion, its only as good as cache, which is temporary.

Fusion doesn’t really have access to edit page, it sources clips from media pool based on reference about what you are selecting in the edit page. Even when you make fusion clip or compound clip, those get duplicated automatically and placed in media pool as well as your timeline, so that fusion can access them as a single clip.
When there is need to access edit page, the only way its via cached frames. So “background” as media source in the MediaIn node and probably adjustment clip as well, will likely work with cached frames. And that makes them less reliable, especially for some type of effects.

I suggest you apply the effect either on the clip itself, or build custom fusion transitions where clips are accessed directly.

If you are applying retiming or speed change effects, than definitely you should make sure you are not doubling on what is happening in fusion. Fusion should apply optical flow etc first if you are retiming with it, and then you apply it in the edit page. So they are independent. And for that you would not use adjustment clip for the reasons I mentioned.

If you are retiming and adding motion blur on top, then either do retiming and make a compound or fusion clip to bake in the animation before opening in fusion to do motion blur or apply third party plug ins in color page for motion blur to respect order of processing.

If you are doing transitions between different clips with this effect, probably better to do by building a custom transition effect so fusion can access the original clips.

Also some of the FX like open FX can be cached by right clicking on them and cashing them. Especially useful in user cache mode. So you can manually cache what you need.

In regards to optical flow + vector motion blur, its not very good, and in some cases it will case artifacts which is typical for simple optical flow. Optical flow generates motion vectors by tracking where pixels are moving. Start to end. When movement is linear than optical flow creates smooth results.

When there is movement in opposite directions, like something passing in front or behind or two movements in opposite direction, like camera movement left, something In the scene moving to the right, than generated motion vectors conflict with each other when optical flow is used. And can cause well known artifacts.

The avoid this you either have to work with stereoscic tools and using backward and forward motion vectors that can be layered over each other, so they don’t conflict, or you need to use algorithms that try to do the same automatically.

My go to filter is RSMB or Real Smart Motion Blur third party plug in from ReVision effects. Well worth it. Its powerful, a lot faster to render and generates a lot better results. That would be my recommendation. Or to generation motion blur from actual animated movement, such as using transform tools.

You could also try motion blur Resolve FX filter or motion plane in the color page. You will need studio version of resolve, I think. Its basically optical flow a bit more optimized for motion blur effects, but still a lot less impressive than RSMB.

BorisFX also has some kind of MotionBlur ML in their continuum line of products. They claim its motion blur with machine learning so it reduces those optical flow artifacts, but I haven’t tested it that much. In my initial tests it generates similar results as RSMB but its slower to render and less convenient to work with in fusion.

The problem is that when I close and reopen the project, sometimes the animation or motion blur gets messed up—some frames freeze or show a frame from a completely different clip. Restarting Davinci doesn’t help because it seems to remember the cache error. The only fixes are duplicating the adjustment layer and then deleting the duplicate (which somehow fixes the original) or completely clearing the cache.

Yes, Resolve has had these unacceptable Cache related issues for YEARS, release after release.....

Does this issue happen with Resolve 20 beta 1?