Voice-over is a production technique where a voice—that is not part of the narrative (non-diegetic)—is used in a radio, television production, filmmaking, theatre, or other presentations. The voice-over is read from a script and may be spoken by someone who appears elsewhere in the production or by a specialist voice actor. Synchronous dialogue, where the voice-over is narrating the action that is taking place at the same time, remains the most common technique in voice-overs. Asynchronous, however, is also used in cinema. It is usually prerecorded and placed over the top of a film or video and commonly used in documentaries or news reports to explain information.