Apple Final Cut Pro 7 - Manual (Page 1244)

The Choke slider adjusts the overall size of the matte, without changing the shape; the
Feather slider blurs the edges of the matte.
The finished matte image
The parameters of the Garbage Matte filters can be keyframed, in the same way as the
parameters of any other filter. This can come in handy if you need to use one of the
Garbage Matte filters to crop out the outside edge of a green screen in a shot where the
camera is panning.
Example: Keyframing Garbage Mattes
In the following example, two sets of keyframes are created to compensate for a simple
pan in the clip being keyed.
To keyframe Garbage Mattes
1 With the playhead on the first frame of a clip, apply and adjust the Four-Point Garbage
Matte filter.
For more details about using this filter, see “Example: Using the Four-Point Garbage Matte
Filter.”
2 Once you’ve created the proper shape for the first frame of the clip, click the keyframe
buttons for the Point 1, Point 2, Point 3, and Point 4 parameters.
Click keyframe buttons
to create keyframes.
Create keyframes for
all four points.
1244 Chapter 72 Keying, Mattes, and Masks