A clapperboard is a device used in film, television, and advertising production to assist with the process of synchronizing the sound and film recordings. Because sound and film are usually recorded separately, they must be matched carefully during the editing process, or the resulting production will feel slightly off to viewers. When the synchronization is extremely poor, it may become almost comic, but even small discrepancies can be very disorienting for viewers.
There are two components to a clapperboard: the clapper, and a slate. The clapper consists of two pieces of wood or plastic which can be snapped together to make a distinctive clacking noise which is easy to find on the sound recording. By matching the sound of the clack to the physical action on the film, the editor can synchronize the sound and film recordings. Clapperboards are sometimes also given away as mementos of film productions.
The slate is used to record information about the production, including the name of the production, the director, the director of photography, and the scene. The take number and camera angle are also written out on the slate. This information assists people in the editing room, allowing them to quickly know what they are looking at by reading the clapperboard.
To use a clapperboard, the film crew sets up the scene, writes out the information on the clapperboard, holds up the clapperboard, and then turns on the camera. Usually, the information on the slate is read out, and then the clapper is snapped. After this, the actors can start performing. The sound on the set is picked up and recorded onto one device, while the film of the scene is stored in the camera.
Clapperboards don't necessarily have to be clacked to mark a scene. Some moviemakers use digital slates, in which a timer is synchronized with the camera. When the clapperboard is held up at the beginning of the scene, the camera records the time on the board, allowing the editor to find the same point in the film or digital recording to synchronize with the sound later.
All of the information on the clapperboard is also recorded in the continuity book for the production, so that people on the crew and in the editing room can look up details later. For example, an editor who wants to find a specific scene to work on could check the continuity book to find out where it should be located.