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# isPreviewing

A Boolean value that indicates whether the layer is rendering video frames from its source.

```
var isPreviewing: Bool { get }
```

## Discussion

A preview layer begins displaying content when you call the capture session’s [`startRunning()`](/documentation/AVFoundation/AVCaptureSession/startRunning()) method. If you associate the layer with an instance of [`AVCaptureMultiCamSession`](/documentation/AVFoundation/AVCaptureMultiCamSession), the system guarantees that all video preview layers display content by the time the blocking call to [`startRunning()`](/documentation/AVFoundation/AVCaptureSession/startRunning()) or [`commitConfiguration()`](/documentation/AVFoundation/AVCaptureSession/commitConfiguration()) returns.

While a session is running, you may enable or disable a video preview layer’s connection to start or stop the flow of video to the layer. You may key-value observe the connection’s [`isEnabled`](/documentation/AVFoundation/AVCaptureConnection/isEnabled) property to observe this property changing, and synchronize any user interface changes to take place precisely when the video resumes rendering to the video preview layer.

---

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