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Dynamic keyframe value using expressions
Hi everyone,
Due to having less work because of the pandemic, I’ve been focussing more on learning expressions in After Effects. I’m new to expressions, so sorry if I’m wasting your time!
I’ve been trying to create a dynamic preset. Almost everything worked well, but I’m facing one problem now, which seems quite easy but I can’t figure it out. I’ll try to explain it as best as possible.
I have a responsive text box, which is tied to the text layer with sourceRectattime(). The animation I’m looking to do is making the text come up inside of the text box, but I want this animation to be dynamic. I already have a layer that calculates what the value needs to be, but I can’t find out how to link this to the keyframes I want to link the value to.
Below a screenshot with the explanation of my problem.

The “Height position” is simply a layer that calculates the height of the text block using sourceRectattime() minus the “offset paths” value, so it shows the exact value of the text height.
So, I’m searching an answer to the questions how I can give a keyframe a dynamic value with expressions.
I hope someone can help me out ☺