• Adobe After Effects Expressions

  Changing Keyframe Time Through Expressions

  Posted by Amir Aizat on August 7, 2016 at 6:01 pm

  Hello, I’m trying to create a template for my team’s video editors working with Premiere Pro.

  It’s supposed to be a transition with adjustable speed by keying s, m, or f in Premiere’s Live Text templates feature.

  English is not my first language, and I am a rookie with expressions (self-taught to boot) so please bear with me.

  The transition has 4 keyframes, 2 in and 2 out. Fast transition will result in -1s for keyframe 2 and +1s for keyframe 3 and the opposite for slow transition. Medium speed will not change the timing of the keyframes. The reason I want to manipulate keyframes instead of using the ease expression is because I want to preserve my speed graph.

  So far I came up with this:

  //Transition Speed
var mod2 = thisComp.layer("Speed (s/m/f)");
var mod2spd = mod2.text.sourceText;

  var ti = thisComp.layer ("Transition A");
  var tp = ti.transform.position;
  var tpk2 = tp.key(2).time;
  var tpk3 = tp.key(3).time;

  if (mod2spd == "s" || mod2spd == "S")
  tpk2+1, tpk3-1
  else if (mod2spd == "m" || mod2spd == "M")
  tpk2, tpk3
  else if (mod2spd == "f" || mod2spd == "F")
  tpk2-1, tpk3+1
  else
  tpk2, tpk3

  valueAtTime
  Obviously I received the orange error message but the error message isn’t helping either, it says “Error at line 0 in the property “Position” of layer 3 (‘Transition A’) in comp ‘Helper Transition’. Object of type Function found where a Number, Array, or Property is needed., an expression was disabled as a result of an error.”

  Can someone explain my mistake and how do I achieve what I wanted to make?

  Thank you.

  Amir Aizat replied 10 years ago 2 Members · 2 Replies
• 2 Replies

• 

  Dan Ebberts

  August 7, 2016 at 6:52 pm

  You can’t change keyframe times with expressions, but this position expression for your transition layer should do what you want:

  
mod2 = thisComp.layer("Speed (s/m/f)");
mod2spd = mod2.text.sourceText.toLowerCase();

  t1 = key(1).time;
  t2 = key(2).time;
  t3 = key(3).time;
  t4 = key(4).time;

  doingIn = time < (t2+t3)/2;

  t = time;
if (mod2spd == "s"){
if(doingIn){
t = linear(time,t1,t2+1,t1,t2);
}else{
t = linear(time,t3-1,t4,t3,t4);
}
}else if (mod2spd = "f"){
if(doingIn){
t = linear(time,t1,t2-1,t1,t2);
}else{
t = linear(time,t3+1,t4,t3,t4);
}
}
valueAtTime(t)


  Dan
• 

  Amir Aizat

  August 7, 2016 at 7:03 pm

  Hi Dan,

  That is amazing! I’ve learned something new today, and I’ve always learned from your other examples.

  Many thanks!

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