Iris transitions impose a growing or shrinking shape on top of the first video. The shape either grows from, or shrinks toward, the center of the image, replacing the first video clip or image with the second.
You can select the shape of the iris, either a diamond, circle, cross, plus, star or square.
The Iris Transition can be In or Out. If it's In, the shape appears to shrink inward from the edges of the screen toward the center. If it's out, the shape appears in the center of the screen, and grows outward until the video it contains fills the whole screen.
Swap video tracks for this transition
Normally the second video clip replaces the first video clip during the transition. Check this option if you want the first to replace the second clip.