Apple Final Cut Pro X (10.0.9) - Manual (Page 212)

Chapter 10 Add transitions, titles, effects, and generators 212
Adjust transitions with multiple images
Several transitions include areas that are filled with still images from the clips on either
side of the transition. For example, this is the Pan Far Right transition (one of the Bulletin
Board transitions).
This image is set by handle
number 4 in the Timeline.
The areas are numbered and correlate to numbered points around the transition in the Timeline.
Adjust transitions with numbered points
1 Select the transition with numbered points in the Timeline.
2 Move the playhead over the transition until you see an area with the same number as one of the
numbered handles in the Timeline.
3 Drag the numbered handle to select the image to fill the area.
4 Continue until you have selected images for all of the areas.