Answers.Body: <p>With my current understanding of how After Effects expressions work, I don't think that can be done.</p>
  <p>According to user Mylenium in <a href="https://community.adobe.com/t5/after-effects-discussions/dynamic-keyframe-value-using-expression/m-p/10130410" rel="nofollow noreferrer">this comment thread</a>,</p>
  <blockquote>
  <p>Keyframe values are read-only</p>
  </blockquote>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2021-10-29T02:41:45.803Z
Answers.LastActivityDate: 2021-10-29T02:41:45.803Z
Answers.UserDisplayName: Stimpson
Body: <p>I'm making a preset for my video projects. It's a shape layer that takes dimensions from a text layer, so the text fits accurately in the shape.</p>
  <p>For this, I'm doing the following:</p>
  <p>Shape Layer &gt; Contents &gt; Box &gt; Box shape (X, Y in pixels) &gt;</p>
  <pre><code>width = thisComp.layer(&quot;Text&quot;).sourceRectAtTime().width;
  height = thisComp.layer(&quot;Text&quot;).sourceRectAtTime().height;
  
  [width, height]
  </code></pre>
  <p>Wich, as I said, it makes the text fit in the box. It works all fine here.
  What I want to do is to animate the shape's dimensions (X and Y property, as said above) using keyframes instead of <code>linear()</code> or other expressions. I want to modify only one specified keyframe (in this case, the last one).</p>
  <p>Thanks in advance!</p>
  
Tags: <after-effects><after-effects-expressions>
Title: Change single keyframe value using expressions
UserDisplayName: spund3
ThreadText: # Change single keyframe value using expressions
  
  (Asked by: username_0 on 2021-08-20)
  
  I'm making a preset for my video projects. It's a shape layer that takes dimensions from a text layer, so the text fits accurately in the shape.
  
  For this, I'm doing the following:
  
  Shape Layer > Contents > Box > Box shape (X, Y in pixels) >
  
  ```
  width = thisComp.layer("Text").sourceRectAtTime().width;
  height = thisComp.layer("Text").sourceRectAtTime().height;
  
  [width, height]
  
  ```
  
  Wich, as I said, it makes the text fit in the box. It works all fine here.
  What I want to do is to animate the shape's dimensions (X and Y property, as said above) using keyframes instead of `linear()` or other expressions. I want to modify only one specified keyframe (in this case, the last one).
  
  Thanks in advance!
  
  **Tags:** after-effects, after-effects-expressions
  
  
  ---
  
  ## 1 answers
  
  ### Answer by username_1 on 2021-10-29. Score: 0
  
  With my current understanding of how After Effects expressions work, I don't think that can be done.
  
  According to user Mylenium in [this comment thread](https://community.adobe.com/t5/after-effects-discussions/dynamic-keyframe-value-using-expression/m-p/10130410),
  
  > Keyframe values are read-only
  
  
  ---
  
  