Using transitions, you can phase out one clip while phasing in the next or you can stylize the beginning or end of a single clip. A transition can be as subtle as a cross dissolve, or emphatic, such as a page turn or spinning pinwheel. You generally place transitions on a cut between two clips, creating a double‑sided transition. However, you can also apply a transition to just the beginning or end of a clip, creating a single‑sided transition, such as a fade to black.
When a transition shifts from one clip to the next, it overlaps frames from both clips. The overlapped frames can either be frames previously trimmed from the clips (frames just past the In or Out point at the cut), or existing frames repeated on either side of the cut. It’s important to remember that when you trim a clip, you don’t delete frames. Instead, the resulting In and Out points form a window over the original clip. A transition uses the trimmed frames to create the transition effect. If the clips don’t have trimmed frames, the transition repeats frames.
A. First clip with trimmed frames at end B. Movie containing both clips and transition C. Second clip with trimmed frames at beginning
A. First clip showing last frame repeated B. Movie containing both clips and transition C. Second clip showing first frame repeated
To see if a transition is single-sided or double-sided and if it has repeated frames, double-click it in the Quick view/Expert view timeline, and view its properties in the Transition contextual control.