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# autoExposureDuration

A special value that may be passed as the duration parameter of a device’s `setExposureModeCustom...` methods to allow the system’s auto-exposure system to manage the exposure duration.

```
class let autoExposureDuration: CMTime
```

## Discussion

This value may be passed to [`setExposureModeCustom(duration:iso:completionHandler:)`](/documentation/AVFoundation/AVCaptureDevice/setExposureModeCustom(duration:iso:completionHandler:)) or [`setExposureModeCustom(lensAperture:duration:iso:completionHandler:)`](/documentation/AVFoundation/AVCaptureDevice/setExposureModeCustom(lensAperture:duration:iso:completionHandler:)) to enable “priority” modes, where some parameters are locked to specified values (given “priority”), whereas the ones specified as “auto” will be continually adjusted by the system to maintain image brightness.

---

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