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An Expression Control to determine the value of a specific keyframe for an effect parameter ?
I have transition comps I like to reuse that include a few layers and several filter effects and for convenience I “publish” (and sometimes consolidate) parameters to a top level null by pickwhipping them to Expression Controls applied to the null (and perhaps adding a multiplier to the pickwhipped generated expression etc) – my understanding and use of AE expressions is quite basic (crude, perhaps ; ).
The comps include some fairly simple and predictable kind of animation of parameters you would expect in a transition effect. Basically there is a really obvious start, mid, and end point to the animation that tends to line up predictably between the various effects and parameters
Here’s what I would like to be able to do… Using the example of a transition that includes a glow effect of some kind… I would like to have an expression control slider (which I would not actually keyframe) that behaves as a Peak Glow Intensity and it would set the value for the middle keyframe of a 3 keyframe animation that created the glow pulse in the comp – and perhaps for another param I would want another expression control slider that represented the start and end value of a 3 point animation (so it would need to set the value of those 2 keyframes). Is there a straightforward way to do this using expressions ? Can markers be used somehow for this purpose ? It would be great if I could build my transition comps so there were START / MID / END markers (or if not Markers perhaps “Master” keyframes at the top level) that I could drag to different time points and the animation would update to follow. Maybe I’m taking the wrong approach and I should not be creating keyframes for the individual effect params at all but rather driving the animation entirely with expressions where the animation could be controlled from another top level layer? Any suggestions (including referrals to relevant published documentation) welcome… Thanks
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2 Replies
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if you wanted to use markers, then you could also set the values with comments in the markers rather than using the sliders, which makes a pretty simple expression.
start = thisComp.marker.key(1);
mid = thisComp.marker.key(2);
end = thisComp.marker.key(3);if (time<=start.time) start.comment;
if (time>start.time && time<= mid.time) linear(time,start.time,mid.time,start.comment,mid.comment);
if (time>mid.time && time< end.time) linear(time,mid.time,end.time,mid.comment,end.comment);
if (time>=end.time) end.comment;to add comments to a comp marker, simply double click the marker and enter a value.
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thanks very much for the suggestion – I’ll experiment with that a bit
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