Shooting technique where the camera rolls without recording live sound; no microphone is used on set, and audio is added later in post-production.
Technical Details
In MOS shots, the camera runs at variable speeds between 6 and 120 fps, as synchronization with the sound tape is not required. The clapperboard is clapped silently or replaced with an "MOS" sign. Modern digital cameras automatically flag MOS takes in the timecode with an "M" flag. The sound mixer records atmosphere (Atmo) or ambient sounds separately at 48kHz/24bit, which are later dubbed in during editing.
History & Development
In 1929, German émigré directors like Ernst Lubitsch introduced the term in Hollywood. Until the 1960s, MOS was standard for action scenes, as heavy blimps (soundproof camera housings) prevented camera movement. With the introduction of self-blimped cameras like the Arriflex 35BL (1972), the proportion of MOS decreased. Today, MOS is experiencing a renaissance through digital post-production and ADR techniques.
Practical Use in Film
Action films like "Mad Max: Fury Road" (2015) shot 80% of their driving scenes MOS, as engine noise made dialogue impossible anyway. Dance sequences are routinely shot MOS to playback, as in "La La Land" (2016). Nature shots and establishing shots are almost exclusively shot MOS. Stunt sequences require MOS, as safety equipment and wind machines are too loud. Slow-motion and time-lapse shots are technically only possible MOS.
Comparison & Alternatives
MOS differs from playback scenes, where music or dialogue is played back. Unlike sync sound recordings, the need for boom microphones and wireless microphones is eliminated. Wild track refers to separate sound recordings on set without the camera. ADR (Automated Dialogue Replacement) replaces dialogue recorded later in the studio, whereas MOS is planned from the outset without original sound. In low-budget productions, MOS is used for cost reduction, as less sound personnel are required.