8 Expressions

If you can dream it, After Effects can build it. Out of the box, After Effects’ presets and effects can do a lot. With expressions, they can do so much more.

Expressions are lines of code added to any keyframable parameter. They’re a means of customizing the way After Effects works. Want to link a single Adjustment Layer to Fill effects on multiple layers? Or loop animation? Or animate a number counter? Expressions!

Expressions could be their own book—in fact, those exist. This chapter does not intend to be a comprehensive list of everything possible with expressions. Rather, it’s intended to be a place to get started and focus on a few practical case studies in which expressions may make your life easier. After finishing this chapter, you should be able to do a web search for comparable expressions that fit your needs, and understand them enough to be able to modify them to your liking.