Answers.Body: <p>This YouTube tutorial explains how to do this:</p>
  <p><strong><a href="https://www.youtube.com/watch?v=nUcBPjlFSTI" rel="nofollow noreferrer">After Effects Quick Tip - How to Add Auto Opacity To Layers and Footage
  </a></strong></p>
  <ol>
  <li>Add an expression to the layer's <code>Opacity</code> property by alt-clicking the stopwatch.</li>
  <li>Paste this expression into the box:</li>
  </ol>
  <pre><code>fadeDuration = .5;
  Math.min(linear(time,inPoint,inPoint + fadeDuration, 0, 100), linear(time,outPoint - fadeDuration,outPoint,100,0))
  </code></pre>
  <p>The layer will now fade in for half a second, and then fade out for half a second based on its in and out points.</p>
  <p>If want to specify the length in <strong>frames</strong> instead of <strong>seconds</strong>, change the first line of the expression to be this:</p>
  <pre><code>fadeDuration = thisComp.frameDuration * 5;
  </code></pre>
  <p>Now the layer will fade in and fade out over a period of <strong>5</strong> frames.</p>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2021-02-14T07:22:36.897Z
Answers.LastActivityDate: 2021-02-14T07:22:36.897Z
Answers.UserDisplayName: Allen Ellis
Body: <p>I want to get the time / duration of the layer, when I stretch or lengthen the layer to produce an effect, for example I want the opacity of a layer to go to 0% 5 frames before the end of the layer, and if I lengthen or I cut that layer that those 5 frames are the same at the end of the layer, regardless of the length of the layer</p>
  
Tags: <after-effects><after-effects-expressions>
Title: Detect duration of layer
UserDisplayName: manuel-ae
ThreadText: # Detect duration of layer
  
  (Asked by: username_0 on 2021-02-10)
  
  I want to get the time / duration of the layer, when I stretch or lengthen the layer to produce an effect, for example I want the opacity of a layer to go to 0% 5 frames before the end of the layer, and if I lengthen or I cut that layer that those 5 frames are the same at the end of the layer, regardless of the length of the layer
  
  **Tags:** after-effects, after-effects-expressions
  
  
  ---
  
  ## 1 answers
  
  ### Answer by username_1 on 2021-02-14. Score: 0
  
  This YouTube tutorial explains how to do this:
  
  **[After Effects Quick Tip - How to Add Auto Opacity To Layers and Footage](https://www.youtube.com/watch?v=nUcBPjlFSTI)**
  
  1. Add an expression to the layer's `Opacity` property by alt-clicking the stopwatch.
  2. Paste this expression into the box:
  
  ```
  fadeDuration = .5;
  Math.min(linear(time,inPoint,inPoint + fadeDuration, 0, 100), linear(time,outPoint - fadeDuration,outPoint,100,0))
  
  ```
  
  The layer will now fade in for half a second, and then fade out for half a second based on its in and out points.
  
  If want to specify the length in **frames** instead of **seconds**, change the first line of the expression to be this:
  
  ```
  fadeDuration = thisComp.frameDuration * 5;
  
  ```
  
  Now the layer will fade in and fade out over a period of **5** frames.
  
  
  ---
  
  