expression: evolving loop

Adobe After Effects Expressions

expression: evolving loop

Posted by Christian Graupner on May 24, 2014 at 5:49 pm

sorry I am new here, not really experienced with expressions and I use a quite of version of afx ( 7 !)

A) the first simple (not for me) question is :
is it possible to write an expression for a loop which is shifting with every repeat.
example : first the movie runs from frame 0 to 12 , then from 2 to 14 , then 4 to 16 , 6 to 18 and so on. the segment length ( 12 in the example) and step width( 2 in the example ) should be adjustable.

B) if yes, could somebody help me out and provide the code ?
feel free to let me know your ‘conditions’

thanks a lot in advance

christian

Christian Graupner replied 10 years, 5 months ago 2 Members · 5 Replies
5 Replies

Dan Ebberts
May 24, 2014 at 6:49 pm

If you have a time-remapped layer, and apply this time remapping expression, I think it will loop the way you have described:

segDur = 13;
segOffset = 2;

f = timeToFrames(time);
segNum = Math.floor(f/segDur);
segPhase = f%segDur;
framesToTime(segOffset*segNum + segPhase)

Dan
Christian Graupner
May 24, 2014 at 8:17 pm

that works brilliant …. thanks so much . when you come to berlin I ll cook a meal for you 😉

btw: would it work as ‘pingpong’ too?
( would run from 0 to 12, from 12reversed to 2 , then from 2 to 14 , back to 4 and so on)

best
christian
Dan Ebberts
May 25, 2014 at 7:06 pm

I think that would be something like this:

segDur = 13;
segOffset = 2;
totalDur = segDur*2-4;

f = timeToFrames(time);
segNum = Math.floor(f/totalDur);
segPhase = f%totalDur;
if(segPhase < segDur)
framesToTime(segOffset*segNum + segPhase)
else
framesToTime(segOffset*segNum + 2*segDur- segPhase – 2)

Dan
Christian Graupner
May 26, 2014 at 1:14 am

of course it works ! in my eyes your are a genius! thank you so much..

all the best

christian
Christian Graupner
April 5, 2016 at 6:16 pm

Hi Dan

Curious if you do see a possibility to make this evolving fwd<>bwd loop behave like a pendulum. I mean that it speeds up exponentially ( ?) to the middle and slows down in the extremes .

in the box below I post your code for the evolving fwd / bwd loop with the straight speed …

segDur = 13; segOffset = 2; totalDur = segDur*2-4;
f = timeToFrames(time); segNum = Math.floor(f/totalDur); segPhase = f%totalDur; if(segPhase < segDur) framesToTime(segOffset*segNum + segPhase) else framesToTime(segOffset*segNum + 2*segDur- segPhase - 2)

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