After Effects allows you to add some expressions to certain properties of layers. These After Effects expressions are basically like a code which affects the behavior of the layer on which an expression is applied. You can apply expressions to the Position, Rotation, opacity, etc of a layer.
There are number of expressions available which you can use and each expression has its own characteristics. So, to create a camera shack or wiggle effect in After Effects, you can use an expression. This expression is applied on the Position property of the layer which you want to shake or wiggle.
First of all, where do we type these expressions. To create a camera shack, expression should go inside the position property of the layer. So, select the layer which you want to shack and hit P on your keyboard. This will open the position property of that layer.
Now, Hold ALT on your keyboard and click on the stopwatch at the position property.
As you ALT+Click on the stop watch, Position Expressions settings and text box will appear.
Now delete transform.position from the text box, and type the wiggle expression instead which is wiggle(x,y) where x and y are in digits, x stands for number of times you want the layer to shack and y stands for the number of frames in which you want that layer to shack.
For example, if i want my layer to shack 5 times in every 15 frames, then my wiggle expression will be wiggle(5,15) adding this expression will tell my layer position properties to move that layer 5 times in any random position in every 15 frames interval.
Make sure you use the expression in correct format. Don’t forget to apply the parenthesis or brackets in your expression as without them, the expression will not work.
Though you can also create camera shack or wiggle effects using the position keyframes and moving the layers manually, it will take lots of time and the end result will not be that impressive as a simple wiggle expression will generate. Apart from that, try experimenting, change the values yourself, notice the results and keep on experimenting. After Effects is all about experimentation.