The three most recent installments of Chris and Trish Meyer’s After Effects Apprentice series have covered three different approaches to grouping layers in After Effects. Each approach has its own strengths and weaknesses; mastering all three means you can choose the right approach for a particular task—or combine them for the ultimate in power and flexibility. Here’s an overview from the third in the series, After Effects Apprentice 09: Expressions.
Expressions allow you tie an individual parameter of one layer either to the identical parameter of another layer, or to a different parameter of the same or different layers—even across compositions. This makes it the most targeted and most flexible approach to grouping in that you can target specific properties, and leave others untouched.
One of the biggest advantages of expressions includes the ability to keyframe just one property or layer and have others follow (and update) automatically. However, this is just one use of expressions; many other functions are possible, including the ability to automatically loop or randomize the animation of a layer.
Watch the entire course: After Effects Apprentice 09: Expressions.