Change single keyframe value using expressions

Question

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!

Answer 1

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,

Keyframe values are read-only