Creating masks from motion paths

You can copy Position, Anchor Point, or an effect's point position keyframes and paste those keyframes to a selected mask. This is useful to create animations that follow the edges of a mask. When you create masks from motion paths, make sure that you copy keyframes from a single position property only--do not copy the keyframes of any other property. For information on motion paths, see Setting layer position.

To create a mask from a motion path:

1. In the Composition window, display the motion path from which you want to create the mask.
2. In the Timeline window, select the successive keyframes along the motion path you want to use as a mask. Click the Position property name to select all the keyframes. Shift-click successive keyframes to select only a few keyframes.
3. Choose Edit > Copy.
4. In the Timeline window, select the layer you want to apply the mask to and expand its properties, or open the layer in its Layer window.
5. Do one of the following:
• To use the motion path as a new mask, choose Layer > Mask > New Mask.
• To use the motion path as a replacement for an existing mask, select the mask you want to replace.
6. In the Timeline, expand the Mask property for the mask you want to create or replace and select the Mask Shape value name.
7. Choose Edit > Paste.