Effect w/ different frame rate than layer

[ug_ffm]

Hi,

I have some 50 fps footage to which I would like to apply a 12.5 fps turbulent displacement effect.
(But keeping the original footage frame rate – so in effect that a different displacement is applied every 4th source footage frame only – and not on every source frame, yet also retaining all source frames – so limiting anything to 12.5 fps would not accomplish the task.)

Does anyone have an idea how I could do this?

The only way I figured was to keyframe the displacement evolution at 12.5 fps and switch off keyframe interpolation.

That does not seem very elegant, though, especially when I want to change displacement evolution paramteters, too …

Thank you very much in advance! I appreciate any hints

[Rick Gerard · Accepted solution]

Since there is no frame rate option in turbulent displace I am guessing that you want to cycle the evolution of a specific number of degrees at 1/4 the frame rate so the displacement stutters instead of being smooth.

If that is correct and you want to keep the same angle offset every time you could simply set two keyframes, one at frame 0 and one at frame 4, change both keyframes to Hold Keyframes, then add this expression:

loopOut("offset")

The offset function will just add to the value of rotation until the layer ends.

The value of the second keyframe will determine the angle change every 4 keyframes. You can just drag the second keyframe up or down the timeline to change the amount of stuttering you get, and if you have the second keyframe selected while the comp is previewing you can double click the second keyframe and change the angle offset.

If you want more control than that it's going to take a more complicated expression.

[Martin_Ritter]

Not sure if this works, but you can reduce fps with posterizeTime(framesPerSecond) expression.

Good luck!

[ug_ffm]

Dear Martin,

that wouldn't work, unfortunately, because the posterizeTime seems to posterize /everything/ – effects, layer content, even transforms …)

But thanks for the idea anyway!

[ug_ffm]

Dear Rick,

brilliant – because so simple.

Thank you very, very much!!