This is yet another place where modern editors have things much easier than in the old days, when trimming frames meant cutting celluloid strips of film. Today, a couple of taps on the keyboard can manipulate In and Out points and trim individual frames in a scene so that there's really no excuse for not dialing in your edits.

Many of today's leading software packages go even further, providing dual-window displays, so the editor can see previews of both incoming and outgoing shots running in real time. This is a great feature when you want to see how trimming affects the shots on both sides of an edit point .

If you watch the great films of yesterday and today, you'll discover they all have something in common. Whether the pace of the scenes is fast or slow, film editors use these matching action techniques to keep their stories moving along. They align the mood of the performances with the pacing of the edits to give every scene (or sequence of scenes) it's own natural rhythm.

Recognizing and finding the ideal visual rhythm for a sequence of shots, and editing it so that it flows smoothly from scene to scene is the difference between someone who just strings scenes together, and a real visual storyteller.

[Sidebar: Breaking the Line]
Another element of matching action is the understanding that movements taking place on the screen will always have a perceived direction.
If the movie violates that notion, our brains have trouble connecting things. Imagine that you and your video club are videotaping a school play entitled Vegetables Are Our Friends. Since there are lots of volunteers, you decide that in addition to the video cameras in the audience, you'll place a camera upstage, behind the scenery, pointing towards the audience.
It's time for Mr. Tomato's big entrance. He enters from the left, and moves to the right. Both upstage and downstage cameras are rolling and have Mr. Tomato in a loose closeup.
In post-production, you'd notice that if you cut between those two shots, Mr. Tomato would be moving left to right in the audience shots, but moving right to left in the upstage camera shots.
That's what's called "breaking the line." Viewers expect actions on screen to have a directional flow. Keeping the camera perspective on one side of an imaginary line that runs parallel to the action maintains that sense of flow.
If you need to break the line, use a neutral shot with the character facing directly towards or away from the camera as a buffer, so that the scene's directional flow momentarily stop…