---
title: AURenderCallback
framework: audiotoolbox
role: symbol
role_heading: Type Alias
path: audiotoolbox/aurendercallback
---

# AURenderCallback

Called by the system when an audio unit requires input samples, or before and after a render operation.

## Declaration

```swift
typealias AURenderCallback = (UnsafeMutableRawPointer, UnsafeMutablePointer<AudioUnitRenderActionFlags>, UnsafePointer<AudioTimeStamp>, UInt32, UInt32, UnsafeMutablePointer<AudioBufferList>?) -> OSStatus
```

## Parameters

- `inRefCon`: Custom data that you provided when registering your callback with the audio unit.
- `ioActionFlags`: Flags used to describe more about the context of this call (pre or post in the notify case for instance).
- `inTimeStamp`: The timestamp associated with this call of audio unit render.
- `inBusNumber`: The bus number associated with this call of audio unit render.
- `inNumberFrames`: The number of sample frames that will be represented in the audio data in the provided ioData parameter.
- `ioData`: The AudioBufferList that will be used to contain the rendered or provided audio data.

## Return Value

Return Value A result code.

## Discussion

Discussion If you named your callback function MyAURenderCallback, you would declare it like this: Discussion You can use this callback function with both the audio unit render notification API (see the AudioUnitAddRenderNotify(_:_:_:) function) and the render input callback (see the kAudioUnitProperty_SetRenderCallback property). As a notification listener, the system invokes this callback before and after an audio unit’s render operations. As a render operation input callback, it is invoked when an audio unit requires input samples for the input bus that the callback is attached to.

## See Also

### Rendering the Audio

- [AudioUnitRender(_:_:_:_:_:_:)](audiotoolbox/audiounitrender(_:_:_:_:_:_:).md)
- [AudioUnitAddRenderNotify(_:_:_:)](audiotoolbox/audiounitaddrendernotify(_:_:_:).md)
- [AudioUnitRemoveRenderNotify(_:_:_:)](audiotoolbox/audiounitremoverendernotify(_:_:_:).md)
- [AudioUnitRenderActionFlags](audiotoolbox/audiounitrenderactionflags.md)