# MOS

Source: https://storiara.com/glossary/mos
Last updated: 2026-09-14
Author: Spencer Kaufman, Storiara

> MOS is a slate and report notation meaning a shot is filmed without sync sound. The camera rolls but the production sound mixer doesn't record for that take. It's used for inserts, cutaways, high-speed shots, and anything where the audio will be replaced or isn't needed. The letters' origin is disputed.

## When crews shoot MOS

The usual candidates are shots where production sound is useless or impossible:

- Inserts, like a hand picking up keys or a phone screen
- High-speed or overcranked shots, where the audio would be slowed down anyway
- Drone shots and car-mount driving footage with engine and wind noise
- Most [second unit](https://storiara.com/glossary/second-unit) work
- Wide establishing shots with no dialogue
- Shots with a loud practical effect where the mixer can't protect the gear

Music video performance takes are a special case: playback is running and the camera may roll MOS, but the track is synced in post from the playback timecode.

## How it goes on set

The 1st AD calls it with the roll: "This is MOS. Roll camera." There's no "roll sound" or "speed" from the mixer. The [2nd AC](https://storiara.com/roles/second-assistant-camera) puts MOS on the slate, often with a quick hand-drawn line or a sticker, and holds it in frame closed. On the camera report, the take gets MOS in the notes column.

A camera report line looks like:

| Scene | Take | Clip | Notes |
|---|---|---|---|
| 42B | 1 | A014C007 | MOS, insert on keys |
| 42B | 2 | A014C008 | MOS, circled |

## Where it trips people up

The most common problem is a surprise line. The director calls MOS for a wide, then in the moment asks an actor to shout something. Now there's no audio. A sound mixer who hears "MOS" but keeps a track rolling for reference can save that. The other problem is the clap: an AC who claps an MOS slate out of habit makes the assistant editor think there's matching audio and go looking for it.

On the [camera report](https://storiara.com/glossary/camera-report) and [sound report](https://storiara.com/glossary/sound-report), make sure MOS is marked in both places, or noted as "sound rolling for reference." Mismatched reports are what slow down dailies syncing.

## Related habits

Shooting MOS doesn't mean the sound department goes idle. It's often the window when the mixer grabs [room tone](https://storiara.com/glossary/room-tone), wild lines, or effects recordings while the camera team handles inserts.

## Frequently asked questions

### What does MOS stand for?

Nobody agrees. The popular story is a German-accented director saying "mit out sound," but there's no solid evidence for it. Other explanations include "motor only sync" and "minus optical sound." Crews just say "M-O-S."

### How do you slate an MOS shot?

Write MOS on the slate. The 2nd AC usually holds the slate with the sticks closed, or with fingers between them so nobody claps by habit, since there's no audio to sync.

### Should sound still record on MOS shots?

Sometimes. Mixers often roll anyway for reference or effects on things like a car pass. If sound is recording, it's no longer strictly MOS, so say so on the reports.