Here, you'll add two clips to the trackgroup with a transition between them.
1 Click the topmost track on the All trackgroup to select it. The track turns
a lighter gray color when selected.
By default, the topmost track is a layer track, which is designed for
consecutive clips with no transitions between them. You want to create
a transition between two clips, so you'll need a transition track.
2 On the Mixer menu bar, open the Tracks menu and choose Convert To
Transition Track.
The track is changed to a transition track that is taller than the original,
with room for two tracks and a transition.
TIPYou can right-click the track to access the same menu options.
3 From the Tracks menu, choose New Clips > From Files.
Combining Motions with the Motion Mixer | 703