• Adobe After Effects Expressions

  I must be busy this morning, 2 posts!

  Posted by Olly Bea on April 11, 2008 at 10:56 am

  Hi

  I have this expression for opacity:

  g = thisComp.layer(“Bass 3”).effect(“Both Channels”)(“Slider”);

  if (g<5 || g>5) 100 – time*20 else 0

  I am trying to get the layer’s opacity to turn on (100%) then fade out over 5 secs if the value from the audio (converted audio keyframes) is greater than 5. But if the value from the converted audio is less than 5, opacity stays at 0%. Does anyone know where I am going wrong?

  Thanks, Olly

  P.S. Sorry Bert Brown I tried that link and the code didn’t seem to work.

  Olly Bea replied 18 years, 1 month ago 2 Members · 2 Replies
• 2 Replies

• 

  Filip Vandueren

  April 11, 2008 at 1:37 pm

  Hi olly,

  The trouble with expressions is, they recalculate every frame, so the expression does not know that there was a peak a few frames ago.
  The solution is to actively look back at every frame for the last 5 seconds to see if there was a frame that peaked.
  This seems to work:

  
prop=thisComp.layer("Audio Amplitude").effect("Both Channels")("Slider");

  threshold=5;
  fadeOut=5; // in seconds

  t=time;
  while (t>time-fadeOut) {
  if (prop.valueAtTime(t)>=threshold) {
  break;
  }
  t-=thisComp.frameDuration;
  }

  linear (time, t, t+fadeOut, 100, 0)

• 

  Olly Bea

  April 11, 2008 at 2:26 pm

  that works brilliantly! Thanks loads

Reply to this Discussion! Login or Sign Up