Masks in Motion

Masks in Motion

Ahead of Chapter 7’s more detailed discussion of rotoscoping,
here are the basics to put a mask in motion.
Alt/Option+M sets a mask keyframe to all unlocked layer
masks. Mask movement can be eased temporally, but there
are no spatial curves; each mask point travels in a completely
linear fashion from one keyframe to the next. An
arced motion requires many more keyframes.

You can only adjust a mask point on one keyframe at a
time, even if you select multiple Mask Path keyframes
before adjusting.
To arc or offset the movement of a mask animation, you
can duplicate the masked layer and use it as an alpha track
matte for an unmasked source of the same layer (see Chapter
7 for more); you can then keyframe and transform its
position and anchor point like any animated layer, with
curved paths and offsets.
Move, Copy, and Paste Masks
Copy a mask path from any compatible source
. A Mask Path property from a separate Mask or Layer
. A Mask Path keyframe from the same or a separate
Mask
. A Mask Path from a separate Adobe application such as
Illustrator or Photoshop
and paste it into an existing Mask Path channel, or paste it
to the layer to create a new Mask. If there are any keyframes,
they are pasted in as well, beginning at the current
time; make sure they don’t confl ict with existing keyframes
in the Mask Shape.
To draw an entirely new shape for an existing, keyframed
Mask Path, use the Target menu along the bottom of
the Layer panel to choose the existing mask as a target,
and start drawing. This replaces the existing shape