Apple Final Cut Pro 7 - Manual (Page 774)

2 Drag the wipe matte clip to the Wipe Matte clip well.
This clip determines the wipe between the two Timeline clips. Any white areas in this clip
will display the first clip. Any black areas in this clip will display the second clip.
In the resulting effect, the media element wipes across the screen to reveal the next shot
from right to left.
Custom Transition Using One Clip
You can use the animated luma values of just a single clip to create complex animated
transition effects.
To create a custom transition using one clip
µ
Drag a wipe matte clip to the Wipe Matte clip well.
This clip determines the wipe between the two Timeline clips. Any white areas in this clip
will display the first clip. Any black areas in this clip will display the second clip.
Alpha Transition Using the Mid-point Offset Slider
Instead of using the wipe matte to determine the change from the first Timeline clip to
the second Timeline clip, your main media element clip could momentarily fill the frame
at some point during the transition. Using the Mid-point Offset slider, you can time the
cut from the first clip to the second clip to occur exactly at the moment the frame is filled
with the media element.
774 Chapter 47 Adding Transitions