Expressions in After Effects – Part 1

Posted 3rd December 2010 by Andrew

In two of my recent blog posts titled ‘Happy Thanksgiving from Media Lightbox’ and ‘Happy Halloween from Media Lightbox’ I created two animations both made in Adobe After Effects.

As like all (or at least most) of the videos/animations I make, I try to learn something new and then put it into practise, which is what I was able to do with these two animations. The thing I leant a little more about in these animations were Expressions in After Effects.

What are Expressions in After Effects?
First off ‘what are Expressions in After Effects?’ I hear you ask… well, Expressions are tools. Just as you use the rotation tool and the Pen tool, you can use Expressions to control animation and composition in After Effects. Most tools in After Effects you will click on their icons and use them by pointing and clicking etc but with Expressions you type commands on the keyboard. These commands must be written in a language and the language that After Effects uses is called JavaScript.

Why use Expressions in After Effects?
Good question… as a designer I normally run away at the first sign of coding talk and I’ve dodged Expressions for quite some time but after dipping my toe in with these last two animations am hungry to learn more. To answer the question better I will tell you what I used Expressions for in these two animations.

First up the Halloween animation (as can be seen below) at the start of this animation a bat comes into the screen flapping it’s wings and moving up and down a little, both these actions were done using Expressions. I.e. I told After Effects to continually move the bats wings up and down and then move the bat up and down a little too. At the end of the animation another Expression was used to make the group of bats fly round the haunted house in a random order.

The Thanksgiving animation (as can be seen below) used similar Expressions as the Halloween animation i.e. the Turkey moves it’s wings up and down and the boat moves up and down too.

Now I could have key framed each of these up and down movements for each element in After Effects but it would taken me literally hours of work and it if it needed changed i.e. the wings need to move quicker etc you would have to go through all the key frames again! What Expressions do or at least what mine done in the examples above is with one line of code I made the wings move up and down forever!… and at the speed I wanted!… if I wanted to change the speed it would only takes seconds!

This is a very basic use of Expressions but it’s a start!… the use of Expressions is endless. In Monday’s post I will tell you what Expressions I used for these animations and also list some good Expression resources which have helped me.

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