---
title: rdd18InstanceUID
framework: AVFoundation
role: symbol
role_heading: Type Property
platforms: [iOS 27.0+, iPadOS 27.0+, Mac Catalyst 27.0+, macOS 27.0+, tvOS 27.0+]
path: avfoundation/avcaptureancillarydatauserkey/rdd18instanceuid
---

# rdd18InstanceUID

An AVCaptureAncillaryDataEncoder key corresponding with the optional RDD18 user defined metadata Instance UID

## Declaration

```swift
static let rdd18InstanceUID: AVCaptureAncillaryDataUserKey
```

## Discussion

Discussion Clients may set the Instance UID with AVCaptureAncillaryDataEncoder/setUserInstanceUID:userUdamVersion: