---
title: kAudioUnitProperty_RenderContextObserver
framework: audiotoolbox
role: symbol
role_heading: Enumeration Case
path: audiotoolbox/kaudiounitproperty_rendercontextobserver
---

# kAudioUnitProperty_RenderContextObserver

The block that the system calls when the rendering context changes.

## Declaration

```occ
kAudioUnitProperty_RenderContextObserver
```

## Discussion

Discussion If your Audio Unit creates auxilliary realtime rendering threads, set the value of this key to the AURenderContextObserver block you want the system to execute. The system executes your block when the rendering context changes. important: The block you provide is for system use only. Audio Unit hosts must not attempt to interact with the audio unit through this block.

## See Also

### Host App Workgroup

- [AURenderContextObserver](audiotoolbox/aurendercontextobserver.md)
- [AudioUnitRenderContext](audiotoolbox/audiounitrendercontext.md)