# audioLatencyMs, the hidden macOS AirPlay latency setting

> What the undocumented com.apple.airplay audioLatencyMs preference does, where macOS reads it, how to set and remove it in Terminal, and what to watch out for.

Updated 2026-10-06. Canonical page: https://lagless.app/guides/audiolatencyms-explained/

> `audioLatencyMs` is an undocumented integer preference in the `com.apple.airplay` domain that overrides the 2000 ms buffer macOS uses for AirPlay system audio. It's read by the root process `AirPlayXPCHelper`, so it must be written as root, and it only applies after that process restarts. Values below 350 ms are not safe.

## Where macOS reads it

`AirPlayXPCHelper` runs as root and reads the preference from root's preferences (`/var/root/Library/Preferences/com.apple.airplay.plist`), then from `/Library/Preferences`. Your own user preferences are never consulted, which is why `defaults write` without `sudo` does nothing. Its log confirms the override: `Overriding audio latency: 350 ms`. Both findings come from the [Preroll research notes](https://github.com/ksha23/preroll/blob/main/NOTES.md) and match our own logs.

## Setting it by hand

```
sudo defaults write com.apple.airplay audioLatencyMs -int 350
sudo killall -9 AirPlayXPCHelper
```

The engine is built once per process, so the second line restarts it; launchd starts it again on demand. Your AirPlay speaker disconnects, so choose it again from Control Center. Preroll notes that a plain `killall` sometimes leaves the process running, hence `-9`.

## Checking it

```
sudo defaults read com.apple.airplay audioLatencyMs
```

## Removing it

```
sudo defaults delete com.apple.airplay audioLatencyMs
sudo killall -9 AirPlayXPCHelper
```

## Things to watch

- **Never go below 350 ms.** [At 250 ms the speaker goes silent.](/guides/airplay-silent-at-250-ms/)
- **Every change drops the speaker.** That's the restart, not a fault.
- **It's undocumented.** Apple can change or remove it in any macOS release.

[Lagless](/) wraps exactly these steps in a menu bar app: one approval instead of `sudo` each time, a range check, the speaker's live delay, and an undo.

## Questions

### Is it safe to use?

It's a preference macOS already supports, and removing it restores the default. The risk is choosing a value too low, which mutes AirPlay until you raise it.

### Does it work for AirPlay from inside apps?

It changes the system-wide AirPlay audio path. Apps that send AirPlay themselves manage their own timing.

## Sources

- [Preroll research notes](https://github.com/ksha23/preroll/blob/main/NOTES.md)
- AirPlayXPCHelper log on macOS 15.7.4