User Guide

CHAPTER 4
134
Managing Layers
You can specify whether the layers overlap or are arranged end to end. For overlapping
layers, you determine how long the layers overlap and whether they cut or crossfade from
one to the next. If you specify a crossfade, After Effects creates opacity keyframes that
control how the layers fade into each other.
Overlapping layers can have opacity keyframes set automatically
to create a crossfade.
For a layer to be sequenced, its duration must be less than the length of the composition
so that it leaves time for other layers. If you plan to sequence still-image footage that you
haven’t imported yet, choose File > Preferences > Import before you import, and specify
a short Still Footage duration. If you’ve already imported still images that are the length of
the composition, you can trim all of them at once by selecting all of the still image layers,
positioning the current-time marker to set the duration you want them to have, and
pressing Alt+] (Windows) or Option+] (Mac OS).
To arrange layers in a sequence:
1 In the Timeline window, hold down Ctrl (Windows) or Command (Mac OS) and select
layers in sequential order, beginning with the layer you want to appear first.
2 Choose Animation > Keyframe Assistant > Sequence Layers.
3 In the Sequence Layers dialog box, do one of the following, and then click OK:
• To arrange the layers end to end, leave the Overlap option unselected.
• To overlap ends of layers, select the Overlap option and type a duration in timecode for
how long the layers should overlap.
4 If you selected the Overlap option in step 3, choose a Crossfade option to specify which
layers’ opacity After Effects adjusts to create crossfades.
• If none of the selected layers uses an alpha channel or mask, choose Front Layer Only.
• If any of the selected layers uses an alpha channel or a mask, choose Front & Back Layers.
UG.book Page 134 Wednesday, February 21, 2001 12:05 PM