After Effects Tutorial Number 1

After Effects Tutorial | Expressions

Melanie Lerner | November 5, 2010

http://www.videocopilot.net/basic/tutorials/09.Expressions/

In this tutorial, Andrew Kremer unlocks expressions for the After Effects user. Expressions are a scripting language for the program that have many endless variables and possibilities, which lets you add in special features not found in the effects bar of the program. To add an expression you must alt + click on a stopwatch (say for position, rotation, or opacity). The expression dialogue box will then appear. The default settings should show up on screen as transform + position (if you are animating position). To change the default you can type in a new expression like wiggle (12, 5). The numerical values tell you two things. First how many times a second the wiggling will occur (in this case 12), and second how much it will occur, in this case 25 units/pixels. To close the expression box, click outside of it.

By animating the expressions in this way, however, the entire layer has an expression added onto it. If however, you want to start and stop the expression so it only occurs at certain points in the animation sequence, then you have to utilize slider control. Slider control doesn’t affect the footage, just the value you want something to have. To get slider control to appear you will have to go to the effect toolbar, click expression controls, and then slider control. You then delete the section of the code that says how often something will occur (the second number) and click and drag the pic width to the slider control bar. The pic width looks like a spiral. At this point, the expression will automatically write itself a new code. This way allows for more control so that the user can add in keyframes to start and stop the expression as he/she chooses.

You can add expressions to other things as well, such as to the opacity. You would use the same technique as before, alt + click the opacity stopwatch, then drag the pic width to the slider control. You can further link layers together so that one expression is used for all without recoding it each time by simply copying and pasting the code. When layers are linked together and you only want to change one part of one of them without affecting the others, you can add a divide or multiply sign after the code to animate differently just that one specific part.

To erase an expression you alt + click the stopwatch or alt + click the = sign. I found the tutorial was effective at demonstrating and helping better understand what are expressions and the ways in which to incorporate them into an animation project. It is, in short, a simple math formula that produces powerful results.