Generator with Effect doesn't update correctly during playback

[latenitefilms]

Apple Feedback Assistant ID: FB12359441

THE PROBLEM:
I have a static Solids > Custom Generator and a WAV file inside a Synchronised Clip. The Generator has an Effect applied to it. The Effect uses an FxPlug4 Filter with kFxPropertyKey_VariesWhenParamsAreStatic set to YES.

When editing the footage on the timeline and during playback/rendering/exporting, Final Cut Pro will display the wrong frames - it is using a cached version of the frames, rather than re-rendering the Generator, even though the Generator has an effect on it that varies even when the parameters are static.

However, if you skim the clip in the timeline, it shows the correct frames. It also shows the correct frames if you playback frame-by-frame (i.e. hold down the right arrow key).

THE WORKAROUND:
This problem doesn’t happen if you apply keyframes to the Color Published Parameter. Using keyframes seems to “trick” the Generator into rendering each frame.

WHAT RESULTS I EXPECT:
I expect that if you have kFxPropertyKey_VariesWhenParamsAreStatic set to YES, it will force any asset (i.e. video clip, generator, compound clip, multi-cam clip, synchronised clip) to render each frame and not use a cached value.

NOTES:
This was originally discussed in FB12179665, and closed as “change required from 3rd party”, which I believe is incorrect, and it’s still a Final Cut Pro bug.