Adobe After Effects CS3 - Manual (Page 118)

AFTER EFFECTS CS3
User Guide
113
See also
“Preview video and audio” on page 120
Nesting, precomposing, and pre-rendering
About nesting and precomposing
Nesting is the inclusion of one composition within another. The nested composition appears as a layer in the
containing composition.
If you want to group some layers that are already in a composition, you can precompose those layers. Precomposed
layers are placed in a new composition (sometimes called a precomposition), and the new composition becomes the
source for a single layer in the original composition. The new composition appears in the Project panel and is
available for rendering or use in any other composition.
You can also nest compositions by adding an existing composition to another composition, just as you would add a
footage item to a composition.
Note: To open a precomposition, Alt-double-click (Windows) or Option-double-click (Mac OS) it in the Timeline panel.
To open the composition that contains the current precomposition, click the Open Parent Composition
button at the
top of the Timeline panel.
Precomposing and nesting are very useful for managing and organizing complex compositions.
By precomposing and nesting, you can do the following:
Apply complex changes to an entire composition You can create a composition that contains multiple layers, nest
the composition within the overall composition, and animate and apply effects to the nested composition so that all
of the layers change in the same ways over the same time period.
Reuse anything you build You can build an animation in its own composition and then drag that composition into
other compositions as many times as you want.
Update in one step When you make changes to a nested composition, those changes affect every composition in
which it is used, just like changes made to a source footage item affect every composition in which it is used.
Alter the default rendering order of a layer You can specify that After Effects render a transformation (such as
rotation) before rendering effects, so that the effect applies to the rotated footage.
Add another set of transform properties to a layer The layer that represents the composition has its own properties,
in addition to the properties of the layers that it contains. This allows you to apply an additional set of transforma-
tions to a layer or set of layers.
For example, you can use nesting to make a planet both rotate and revolve (moving like the Earth, which spins on its
own axis and also travels around the Sun). To do this, you animate the Rotation property of the planet layer,
precompose that layer, modify the Anchor Point property of the precomposition layer, and then animate the
Rotation property of the precomposition layer.
Because a precomposition is itself a layer, you can control its behavior using layer switches and composition switches
in the Timeline panel. You can choose whether changes made to the switches in the containing composition are
propagated to the nested composition. To prevent layer switches from affecting nested compositions, choose Edit >
Preferences > General (Windows) or After Effects > Preferences > General (Mac OS), and then deselect Switches
Affect Nested Comps.