1: Create new project
Go to File> New Project. Choose an Aspect Ratio of 16:9 and a Frame Rate of 30 fps. Choose No Theme. Untick ‘Automatically add Cross Dissolve’.
2: Import clips
Go to File>Import>Movies. Browse to the Transition Sources folder on our disc. Click ‘Create new Event’. Tick ‘Optimize video’. Click Import.
3: Project Properties
To change the default transition from 15 frames, go to File>Project Properties. Drag the Transition Duration slider to 2:00 seconds. Click OK.
4: Adjust Preferences
Our source clips vary in length. To make them all last 5 seconds, go to iMovie>Preferences. Set ‘Clicking in Event Browser selects’ to 5:00.
5: Add clips
Click on each clip in turn and drag a 5-second selection to the Project window. As each clip runs for 5 seconds, we have a total project duration of 20 seconds.
6: Add transition
Drag a Cross Dissolve between the first two clips. It will reduce the length of the overlapping clips to 3 seconds each. Total project duration loses 2 seconds.
7: Reduced duration
Adding two more transitions, they eat into the duration of the adjacent clips to create 2-second dissolves. This reduces the total duration from 20 seconds to 14.
8: Open Inspector
You can change the way the transitions overlap with the clips to lengthen the total duration of the project. Double-click on a transition to open the Inspector.