About the Two-Up Display in the Canvas
You can drag the pointer in the Transition Editor to trim the transition and change the
duration of the transition or the actual location, or edit point, where the transition
occurs between two clips. When you do this, a dual frame display appears in the
Canvas to show how your change affects the clips surrounding this transition.
 The frame on the left: This displays the current frame at the transition’s start point in
the outgoing clip.
 The frame on the right: This displays the current frame at the transition’s end point in
the incoming clip.
The name of each clip is at the top of each display and the timecode for the transition’s
start or end point is visible at the bottom of each display.