Re: Slow something down using expressions

As you've discovered, controlling speed with expressions is not a simple task. It's a little tricky to explain, but basically when you do a calculation based on an instantaneous speed value (like a keyframed slider), the result you get at any given frame is what you would get if the speed had always been that value. The result is a phase mismatch that will cause your animation to behave in unexpected ways.

The solution can be complicated. You need to calculate the cumulative affect your slider control has had on all previous frames. It can be a fairly simple calculation if you only use linear keyframes, but if you use any easing, you'll need to do a frame-by-frame integration/accumulation, starting at the layer's In Point, and moving forward to the current frame.

Dan