In iMovie, you can add an effect like a fade or a dissolve to blend the transition between two clips. You can also change the length of the transition after adding it.
When you make a transition longer, iMovie uses additional, unused portions of each clip to create the transition. If there isn't enough unused portions of the clips, an alert appears, and you won't be able to make the transition longer. To make the transition longer, shorten the clips on both sides of the transition.
Change the length of a transition
- Double-click a transition in the timeline.
- Enter a new duration.
- Click Apply. To change the length of all transitions, click Apply to All.
If iMovie won’t let you make the transition between two clips longer, shorten one or both clips.
Shorten clips to make a transition longer
- In the timeline, drag the end of the first clip to the left.
- Drag the beginning of the second clip to the right.
- Double-click the transition, enter the duration, then click Apply. If you still can't lengthen the transition, shorten the clips until you can enter the duration you want.