• Adobe After Effects Expressions

  How to match Rotation of Position Keyframes and Trapcode Stroke Offset

  Posted by Ness Lange on March 11, 2021 at 3:04 am

  I’ve been creating a circular motion of an emitting light, that moves forward on every beat thanks to Soundkey integrating function (Rising values depending on beat):

  a = 150;
  f = 1/30;
  t = thisComp.layer("Keys").effect("Sound Keys")("Output 1");
  x = a*Math.sin(f*2*Math.PI*t)+thisComp.width/2;
  y = a*Math.cos(f*2*Math.PI*t)+thisComp.height/2;
  [x,y]

  I’ve linked this with the Trapcode particular, thus a nice particle trail emerges.

  I could have also used Dan Ebberts speed method. Maybe I have to because here comes the issue: I’ve applied Trapcode stroke to the circle and want the taper to move with the particles.

  Therefor I want to animation the offset, the reason being it drives the taper. However if I feed SoundKeys into the offset, they are out of phase:

  Expression Offset: 

  1/30*2*Math.PI*thisComp.layer("Keys").effect("Sound Keys")("Output 1");

  Hence the angular momentum must be different. But why?

  This might all seem abstract so I’ll attach a picture of what I am wanting to do:

  

  Ness Lange replied 5 years, 5 months ago 1 Member · 1 Reply
• 1 Reply

• 

  Ness Lange

  March 12, 2021 at 11:58 pm

  So it just harmonizes with:

  f*100*thisComp.layer("Keys").effect("Sound Keys")("Output 1");

  Don’t know why exactly this relation. Probably because of the way the’offset’ is defined.

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