VOICE OVER

Voice-over (also known as off-camera or off-stage commentary) 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.

Voice-overs are used in video games and on-hold  messages, as well as for announcements and information at events and tourist destinations. It may also be read live for events such as award presentations. 

Voice-over is added in addition to any existing dialogue and is not to be confused with voice acting or the process of replacing dialogue with a translated version, the latter of which is called dubbing or revoicing.

Techniques

Character device - Charactering techniques in voice-overs are used to give personalities and voice to fictional characters.

Creative device - In film, the filmmaker distributes the sound of a human voice (or voices) over images shown on the screen that may or may not be related to the words that are being spoken. Consequently, voice-overs are sometimes used to create ironic counterpoint. Also, sometimes they can be random voices not directly connected to the people seen on the screen. In works of fiction, the voice-over is often by a character reflecting on his or her past, or by a person external to the story who usually has a more complete knowledge of the events in the film than the other characters.

Voice-overs are often used to create the effect of storytelling by a character/omniscient narrator. voice-over can be used to aid continuity in edited versions of films, in order for the audience to gain a better understanding of what has gone on between scenes.

Educational device - The voice-over has many applications in non-fiction as well. Television news is often presented as a series of video clips of newsworthy events, with voice-over by the reporters describing the significance of the scenes being presented; these are interspersed with straight video of the news anchors describing stories for which video is not shown.

Commercial Device - The commercial use of voice-over in television advertising has been popular since the beginning of radio broadcasting.

In the early years, before effective sound recording and mixing, announcements were produced "live" and at-once in a studio with the entire cast, crew and, usually, orchestra. A corporate sponsor hired a producer, who hired writers and voice actors to perform comedy or drama.

Manufacturers will often use a distinctive voice to help them with brand messaging, often retaining talent to a long-term exclusive contract.

Translation - In some countries, voice-over provided by an artist is commonly used on television programs as a language localization technique, as an alternative to full dub localization.