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Chapter 12 Keyingandcompositing 405
Compositing
Compositing overview
Compositing refers to combining parts of two or more video clips into a single image.
There are a number of ways to combine video images in Final Cut Pro:
 Transitions: All video transitions involve combining the end of one clip with the start
of a second clip, which results in a combination of the two clips appearing at the
same time during the transition.
 Keying: All keys involve compositing a foreground image over a background image.
 Alpha channels: Many computer-generated video clips have an alpha channel—a
built-in mask—that denes precisely the areas of the clip that are composited over
a background clip. These require no key setup and generally just automatically
work. Many eects, such as Transform and Distort; generators, such as Shapes and
Timecode; and titles use alpha channels.
 Compositing: Each video clip in the Timeline has a set of Compositing settings. These
are used when you want to combine clips without using the key eects.
Use alpha channels
Alpha channels provide an easy way to composite one image over another. Using an
application like Motion, an Apple application designed to work with Final Cut Pro, you
can create still images and video clips that have alpha channels. Alpha channels can
be thought of as having a built-in keyer—when you use the key eects you are
creating a mask that is used in the same way a clip with an alpha channel is used
for compositing.
Below is an example of a clip with an alpha channel, showing the image that lls the
alpha channel.