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Converting expressions to keyframes
In some situations, it may be useful to convert an expression to keyframes. For example, if
you want to freeze the values in an expression for a period of time, you can convert the
expression to keyframes and then adjust the keyframes accordingly; if an expression takes
a long time to evaluate, you can convert it to keyframes so that it renders faster. When you
convert to keyframes, After Effects evaluates the expression, creating a keyframe at every
frame, and then disables the expression.
To convert an expression to keyframes:
In the Timeline window, select the property in which the expression is written and choose
Animation > Keyframe Assistant > Convert Expression to Keyframes.
Creating expressions with the pick whip
Use the pick whip to create expressions that link the values of one property or effect to
another. For example, link the Rotation property of layer 1 to the Rotation property of layer
2 to make layer 1's rotation values the same as layer 2's; or, link a camera's Point of Interest
property to the Position property of another 3D layer to make the camera follow the layer
as it moves through space.
Selecting properties and values with the pick whip
To use the pick whip, click the pick whip icon ( ) and drag it to another property or to a
specific property value. Once you select a property or value, After Effects automatically
inserts the appropriate expression in the expression field at the location of the cursor; if
text is already selected in the expression field, that text is replaced by the new expression
text. If the cursor is not in the expression field, all text in the field is replaced by the new
text.
Determining which values are used in an expression
Different properties in After Effects have different value dimensions (1D, 2D, 3D, or 4D)
depending on the number of value parameters they have. In the expression language,
property values are either single values (numbers) or arrays (see "Numbers and arrays" on
page 251). Arrays, such as position values, are always enclosed in square brackets and
separated by commas; a single value, such as an opacity value, does not use brackets.
Following are examples of different property-value dimensions:
1D values: Rotation ° and Opacity %
•
2D values: Scale [x=width, y=height], Position [x, y], and Anchor Point [x, y]
•
3D values: Scale [width, height, depth], Position [x, y, z], and Anchor Point [x, y, z]
•
4D values: Color [red, green, blue, alpha]
•
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