When you're using multiple camera devices, a transition controls the image change as you move from one camera view to another. Different transition types influence the shift between keyframes:
Linear The camera view shifts cleanly from one camera to the next, at a constant pace between frames.
Ease In Makes the transition start slowly then gain speed.
Ease Out This option slows down the transition before it stops.
Ease In-Out Combines Ease In and Ease Out, so slow at start, speeding up, then slow to stop at end.