Varying curvepath speed...

Recently I did an animation with a camera that follows a curvepath. However, I would like to change the speed with which the camera follows the path at different points. I know I can set the number of frames it takes to traverse the path in the curve settings, but I want to make it go faster at specific points and slower at others.

My initial thought was, “Oh, I’ll go into the IPO editor and stretch/squish parts of the the curve there to change the speed at various spots.”

But, it seems that animations based on curvepaths don’t use keyframes, and therefore their data isn’t stored in the IPO graphs.

What to do?

The path length is an “auto-animation” tool. It is a simple way to get an animation up and running, but as you have found out, when you want more control, you need to alter the curve. There is no curve by default, so you have to create one.

With the curve selected, open an IPO window.
By default, the IPO window will say “Object”, but click the drop down and change to path.
You should see a single IPO channel called speed.
CTRL-Click inside the IPO window then CTRL-Click again and you will have a speed curve for your animation.

At this point, you can no longer control the animation via the pathlen in the curve. You will control the animation via the speed channel IPO curve.