Who will explain the empty mirror to me?

A story is often inconsistent with the movie time, so editing can make an event appear longer or shorter. Omitting editing is a way to express things in a shorter time than actually. One of the commonly used methods is the empty box.

Empty mirror refers to the process before and after two cameras when an actor/character leaves the camera and the camera is in an "empty" state. They are usually time-consuming and repetitive behaviors with no practical (story/plot-driven) effect. For example, the character is taking stairs and climbing mountains.

Because ordinary movies don't let the audience watch the character walk up the stairs for half an hour (unless it has special significance), if you just want to bring out the information that a person is walking up the stairs, then let the character walk up at the bottom of the stairs until he leaves the camera (at this time, the camera is fixed instead of following the role), and then take an empty mirror on the top floor (nobody's floor), and then let the character appear on the stairs and walk up under the same camera. This treatment can save the time of taking the stairs, and the application of empty mirror will not make the connection between the two lenses (the bottom and top of the stairs) too abrupt.

If necessary, you can refer to this explanation, but it is in English (but it is not difficult to have pictures and text explanations, so you can have a look): /title/ ellipse+editing.

In addition, if you are interested in movies, you can read this book: The Art of Film: Form and Style by David Bordwell and Christine Thompson, which is available on Taobao and online.

My Chinese may be a little poor, so get used to it first.