---
title: activeExternalSyncVideoFrameDuration
framework: avfoundation
role: symbol
role_heading: Instance Property
path: avfoundation/avcapturedeviceinput/activeexternalsyncvideoframeduration
---

# activeExternalSyncVideoFrameDuration

The receiver’s external sync frame duration (the reciprocal of its frame rate) when being driven by an external sync device.

## Declaration

```swift
var activeExternalSyncVideoFrameDuration: CMTime { get }
```

## Discussion

Discussion Set up your input to follow an external sync device by calling follow(_:videoFrameDuration:delegate:). note: The value of this readonly property is kCMTimeInvalid unless the AVExternalSyncDevice is actively driving the AVCaptureDeviceInput. This is reflected by the status being either AVExternalSyncDeviceStatusActiveSync or AVExternalSyncDeviceStatusFreeRunSync.

## See Also

### Synchronizing with external devices

- [isExternalSyncSupported](avfoundation/avcapturedeviceinput/isexternalsyncsupported.md)
- [follow(_:videoFrameDuration:delegate:)](avfoundation/avcapturedeviceinput/follow(_:videoframeduration:delegate:).md)
- [unfollowExternalSyncDevice()](avfoundation/avcapturedeviceinput/unfollowexternalsyncdevice().md)
- [externalSyncDevice](avfoundation/avcapturedeviceinput/externalsyncdevice.md)