Thanks for the thoughtful reply Dan. Do you know if there is a way to view the source code for expression function definitions? Ideally I’d like my extendscript velocityAtTime function to be a 1:1 copy in order to avoid unanticipated issues due to assumptions on my part.

I was making small changes to the bounce expression below in order to call it in extendscript:

Realistic Bounce and Overshoot (motionscript.com)

About 10 lines down we see:

v = -velocityAtTime(key(n).time – .001)*e;

According to the expressions documentation the velocityAtTime function lives on the property object: Property — After E… Read more