Post Production: Understanding Match Action
Editors make a comfortable income putting one frame next to another, and one trick of the trade to make their editing flow is to cut with match action. This technique helps mask the fact that you're going from one shot to another.
What Is Matching Action?
When you have two shots that are different takes and different angles, matching action makes it look like one continuous action. It masks the fact that there is a cut. For instance, the character in a wide shot sweeps his hand past the edge of a table, and you cut to a close-up shot of the same action.
Jarring cuts are the opposite of matching action. This can be effective if you are trying to make your audience uncomfortable (as in suspense) or if you want to draw attention to the fact that the audience is watching a movie. However, most of the time people prefer to cover the cut.
If you're cutting from a wide shot to a close-up, lay down your wide shot first, then when you're trying to match the action with the close shot, you'll actually want to go back a few frames earlier on the close-up. Intellectually this seems to go against what you're trying to accomplish, but it allows your eye to "catch up." It takes a fraction of a second for your eye to adapt to the difference of the wider shot to the close action. Try it. It may surprise you, but it works.
When you're moving from a close shot to a wide one, you will slow down your eye if you have the overlap mentioned above. To edit, first lay down your close shot, then, when you have the shot lined up (that is, when the hand is at the same point moving past the table), you should cut out a few frames from the head of the wide shot. Any overlap from close to wide will create a lag in your action.
If This Doesn't Work
Generally, matching action depends on the two shots imitating the same action, but also to have two angles that are different enough that it's not just 'jumping in' like a faulty zoom. Nonetheless, sometimes, no matter how much you've planned, the cuts won't work. First, you can cut-away to 'the kitchen sink'. This is an old school technique where editors, facing two completely unmatchable cuts, would cut to something else in the room, then cut back to the other action. Generally, it's best to cut-away to something that's valuable to the scene. (Just make sure the director gets a shot of something in the room that you can cut-away to.) Finally, if you can't solve it, dissolve it. There's a feature in your edit system called a dissolve. This can take you from one location or time to another, but it can also help solve bad cuts. Artificial looking, this is usually a last ditch effort.
The key to good editing is having the director get the shots you need when the cast and crew are on the set.