I’m always amazed when I meet After Effects users who don’t know about or utilize expressions. I’m no scripting guru, but the few expression tricks I know get used constantly. A couple of simple expressions are extremely useful for visualists, allowing you to quickly pump out incremental clips by just changing slider values.
The creatively titled “After Effects Expressions” (Come on people, Google Juice isn’t the only rationale you need to consider when naming your blog) starts with the basics, but quickly gets into conditional expressions and slider-driven animation, which is visualist gold as far as I’m concerned.
In After Effects, an expression is a Javascript based script in that can either modify a parameter or drive the parameter entirely, like position, opacity, or perhaps a Gaussian blur level. We can add an expression to any parameter that has a stopwatch icon next to the parameter. The exclusion to this rule are Masks parameters like Mask Shape, Mask Feather, etc.
This stuff is coming from Graymachine‘s Harry J Frank, who is also involved in AE Freemart, so you can expect plenty more goodness to come.