A clapperboard, also known as a dumb slate, is a device used in filmmaking and video production to assist in synchronizing of picture and sound, and to designate and mark the various scenes and takes as they are filmed and audio-recorded. It is operated by the clapper loader. It is said to have been invented by Australian filmmaker F. W. Thring.
When sound and picture are out of synchronization, lip flap may occur.
In the silent era the principal requirement of film stock identification during a day's shoot was the slate.
The clapper as two sticks hinged together was invented by F. W. Thring (father of actor Frank Thring), who later became head of Efftee Studios in Melbourne, Australia.     The clapperboard with both the sticks and slate together was a refinement of Leon M. Leon (1903–1998), a pioneer sound engineer. 
The clapperboard combines a chalkboard slate or acrylic board with a set of clapper sticks across the top. The slate displays the name of the production, the scene and "take" about to be performed, and similar information;  a camera assistant holds the clapperboard so the slate is in view of the cameras with the clapper sticks already open, speaks out information for the benefit of the audio recording, then claps the clapper sticks shut. 
The shutting of the clapper sticks is easily identified on the visual track, and the sharp "clap" noise is easily identified on the separate audio track. The two tracks can later be precisely synchronized by matching the sound and movement. Since each take is expressly identified on both the visual and audio tracks, segments of film are easily matched with corresponding segments of audio. 
It is also known as a "dumb slate". 
Finding a way to synchronize visual and audio tracks was essential to traditional filmmaking because film stock reacts to light, not sound.  During a film shoot, the audio track was always recorded by the audio engineer with a separate system on separate media (so-called double-system recording).  (For early sound films, playback of the audio track was synchronized during post-production with sound-on-disc techniques; engineers later figured out how to directly add an audio track to a release print with sound-on-film techniques.) Failure to use clapperboards can prevent the film editor from synchronizing the visual images on film footage with the accompanying audio recordings, as actually happened with the long-delayed film Amazing Grace . 
Methods were later developed to directly record sound to film (technically, a magnetic stripe on film) as part of a single system integrated with the film camera (so-called single-system recording), which was most commonly used with small formats like Super 8 film.  However, single-system recording did not render clapperboards obsolete. First, single-system recording of sound-on-film is "decidedly inferior in audio quality" to traditional double-system recording.  Second, footage from single-system recording is difficult to shoot and edit.  Since the sound playback head cannot block the projector gate and must be placed after the gate, the soundtrack must be offset by several frames (usually 28, 26, or 18 ahead) to maintain sync with the frame in the gate.  With such footage, cutting to the next shot when an actor's lips stop moving will risk cutting off their last syllable, unless the soundtrack is copied and edited on a separate system, and actors must be directed to pause to allow for such cuts.  Because of these technical limitations, the film industry has continued to use double-system recording for professional-quality film projects. 
A traditional clapperboard (i.e., a dumb slate) consists of a wooden slate with a hinged clapper stick attached to its top. A modern clapperboard generally uses a pair of wooden sticks atop either a whiteboard or a translucent acrylic glass slate (the latter being easily legible via the light coming through it from the scene about to be shot). The clapper sticks traditionally have diagonally interleaved lines of black and white to ensure the camera can capture a clear visual image of the clap in most lighting conditions. In recent years sticks with calibrated color stripes have become available.
A digislate is a clapperboard with an inbuilt electronic box displaying SMPTE time codes. The timecode displayed on the clapperboard will have been jam synced with the internal clock of the camera, so that in theory it should be easy for the film editor to pull the timecode metadata from the video file and sound clip and synchronize them together. However, electronic timecodes can still drift during a long shooting day, so the clapper sticks on the clapperboard still need to be closed together in order to ensure there is a way of manually synchronizing the footage and audio if matching the digital timecode fails.
The slate typically includes the date, the production title, the name of the director, the name of the director of photography (DoP) and the scene information — which follows two popular systems:
A verbal identification of the numbers, known either as "voice slate" or "announcement", occurs after sound has reached speed. At the same time or shortly thereafter, the camera will start running, and the clapperboard is then filmed briefly at the start of the 'take' and the clapper sticks are clapped sharply as soon as the camera has reached sync speed. Specific procedures vary depending on the nature of the production (documentary, television, feature, commercial, etc.), and the dominant camera assisting regional conventions. 
A clapper board is generally used to identify all takes on a production, even takes that do not require synchronization, such as MOS takes, which have no sound. When a slate is used to mark an MOS take, the slate is held half open, with a hand blocking the sticks, or closed, with a hand over the sticks.
The clapper loader (or 2nd AC) is generally responsible for the maintenance and operation of the clapperboard, while the script supervisor is responsible for determining which system will be used and what numbers a given take should have. While these are usually fairly obvious once a system has been agreed upon, the script supervisor is usually considered the final arbiter in the event of an unclear situation.
Sometimes a "tail slate" or end slate is filmed at the end of a take, during which the clapperboard is held upside-down. This is done when the slate was not captured at the start of the take due to the camera being set up for the shot in such a way that the board cannot be captured, for example when a specific focus or frame is set up and cannot be altered until the take is complete. Tail slates are also commonly used when the director makes the decision that clapping a slate at the beginning of the scene would be distracting to the actor, such as when filming a highly emotional performance.
A film crew is a group of people, hired by a production company, for the purpose of producing a film or motion picture. The crew is distinguished from the cast, as the cast are understood to be the actors who appear in front of the camera or provide voices for characters in the film. The crew is also separate from the producers, as the producers are the ones who own a portion of either the film studio or the film's intellectual property rights. A film crew is divided into different departments, each of which specializes in a specific aspect of the production. Film crew positions have evolved over the years, spurred by technological change, but many traditional jobs date from the early 20th century and are common across jurisdictions and filmmaking cultures.
Synchronization is the coordination of events to operate a system in unison. For example, the conductor of an orchestra keeps the orchestra synchronized or in time. Systems that operate with all parts in synchrony are said to be synchronous or in sync—and those that are not are asynchronous.
A timecode is a sequence of numeric codes generated at regular intervals by a timing synchronization system. Timecode is used in video production, show control and other applications which require temporal coordination or logging of recording or actions.
A movie camera is a type of photographic camera that rapidly takes a sequence of photographs, either onto film stock or an image sensor, in order to produce a moving image to display on a screen. In contrast to the still camera, which captures a single image at a time, the movie camera takes a series of images by way of an intermittent mechanism or by electronic means; each image is a frame of film or video. The frames are projected through a movie projector or a video projector at a specific frame rate to show the moving picture. When projected at a high enough frame rate, the persistence of vision allows the eyes and brain of the viewer to merge the separate frames into a continuous moving picture.
A clapper loader or second assistant camera is part of a film crew whose main functions are that of loading the raw film stock into camera magazines, operating the clapperboard (slate) at the beginning of each take, marking the actors as necessary, and maintaining all records and paperwork for the camera department. The name "clapper loader" tends to be used in the United Kingdom and Commonwealth, while "second assistant camera" tends to be favored in the United States, but the job is essentially the same whichever title is used. The specific responsibilities and division of labor within the department will almost always vary depending on the circumstances of the shoot.
The role of an assistant director on a film includes tracking daily progress against the filming production schedule, arranging logistics, preparing daily call sheets, checking cast and crew, and maintaining order on the set. They also have to take care of the health and safety of the crew. The role of an assistant to the film director is often confused with assistant director but the responsibilities are entirely different. The assistant to the film director manages all of the directors in development, pre-production, while on set, through post-production and is often involved in both personal management as well as creative aspects of the production process.
A take is a single continuous recorded performance. The term is used in film and music to denote and track the stages of production.
Filmmaking or film production is the process by which a motion picture is produced. Filmmaking involves a number of complex and discrete stages, starting with an initial story, idea, or commission. It then continues through screenwriting, casting, pre-production, shooting, sound recording, post-production, and screening the finished product before an audience that may result in a film release and an exhibition. Filmmaking occurs in a variety of economic, social, and political contexts around the world. It uses a variety of technologies and cinematic techniques.
Principal photography is the phase of producing a film or television show in which the bulk of shooting takes place, as distinct from the phases of pre-production and post-production.
Sync sound refers to sound recorded at the time of the filming of movies. It has been widely used in movies since the birth of sound movies.
In filmmaking, dailies are the raw, unedited footage shot during the making of a motion picture. The term comes from when movies were all shot on film because usually at the end of each day, the footage was developed, synced to sound, and printed on film in a batch for viewing the next day by the director, selected actors, and film crew members. After the advent of digital filmmaking, "dailies" were available instantly after the take and the review process was no longer tied to the overnight processing of film and became more asynchronous. Now some reviewing may be done at the shoot, even on location, and raw footage may be immediately sent electronically to anyone in the world who needs to review the takes. For example, a director can review takes from a second unit while the crew is still on location or producers can get timely updates while travelling. Dailies serve as an indication of how the filming and the actors' performances are progressing. The term was also used to describe film dailies as "the first positive prints made by the laboratory from the negative photographed on the previous day".
MOS is a standard filmmaking jargon acronym used in production reports to indicate an associated film segment has no synchronous audio track.
A script supervisor is a member of a film crew who oversees the continuity of the motion picture including wardrobe, props, set dressing, hair, makeup and the actions of the actors during a scene. The notes recorded by the script supervisor during the shooting of a scene are used to help the editor cut the scene. They are also responsible for keeping track of the film production unit's daily progress. The script supervisor credit typicallysing credits of a motion picture. Script supervisors are a department head and play a crucial role in the shooting of a film. It is the script supervisor's job to monitor the camera shots, seeking to maintain coherence between the scenes.
Double-system recording is a form of sound recording used in motion picture production whereby the sound for a scene is recorded on a machine that is separate from the camera or picture-recording apparatus.
Used in television production and filmmaking post-production, a 2-pop is a 1 kHz tone that is one frame long and placed 2 seconds before the start of a program. It is a simple and effective method of ensuring synchronization between sound and picture in a video or film.
In the post-production process of film editing and video editing, a cut is an abrupt, but usually trivial film transition from one sequence to another. It is synonymous with the term edit, though "edit" can imply any number of transitions or effects. The cut, dissolve, and wipe serve as the three primary transitions. The term refers to the physical action of cutting film or videotape, but also refers to a similar edit performed in software; it has also become associated with the resulting visual "break".
Articles related to the field of motion pictures include:
Multi-image is the now largely obsolete practice and business of using 35mm slides (diapositives) projected by single or multiple slide projectors onto one or more screens in synchronization with an audio voice-over or music track. Multi-image productions are also known as multi-image slide presentations, slide shows and diaporamas and are a specific form of multimedia or audio-visual production.
A sound follower, also referred to as separate magnetic, sepmag, magnetic film recorder, or mag dubber, is a device for the recording and playback of film sound that is recorded on magnetic film. This device is locked or synchronized with the motion picture film containing the picture. It operates like an analog reel-to-reel audio tape recording, but using film, not magnetic tape. The unit can be switched from manual control to sync control, where it will follow the film with picture.
This glossary of motion picture terms is a list of definitions of terms and concepts related to motion pictures, filmmaking, cinematography, and the film industry in general.