---
title: kAudioUnitProperty_MIDIOutputCallbackInfo
framework: audiotoolbox
role: symbol
role_heading: Global Variable
path: audiotoolbox/kaudiounitproperty_midioutputcallbackinfo
---

# kAudioUnitProperty_MIDIOutputCallbackInfo

A read-only CFArray object valid on the audio unit global scope.

## Declaration

```swift
var kAudioUnitProperty_MIDIOutputCallbackInfo: AudioUnitPropertyID { get }
```

## Discussion

Discussion The host will also need to determine how many MIDI output streams the audio unit can generate (and the name for each of these outputs). Each MIDI output is a complete MIDI data stream, such as embodied by a MIDIEndpointRef in CoreMIDI. To do, the host uses this property and retrieves an array of CFStringRefs. the size of the array is the number of MIDI Outputs the audio unit supports each item in the array is the name for that output at that index The host should release the array when it is finished with it. Once the host has determined the audio unit supports this feature, it then instantiates a callback with the unit that the unit will call with MIDI data (see kAudioUnitProperty_MIDIOutputCallback).

## See Also

### Properties

- [kAudioUnitProperty_ElementCount](audiotoolbox/kaudiounitproperty_elementcount.md)
- [kAudioUnitProperty_SupportedNumChannels](audiotoolbox/kaudiounitproperty_supportednumchannels.md)
- [kAudioUnitProperty_AudioChannelLayout](audiotoolbox/kaudiounitproperty_audiochannellayout.md)
- [kAudioUnitProperty_AudioUnitMIDIProtocol](audiotoolbox/kaudiounitproperty_audiounitmidiprotocol.md)
- [kAudioUnitProperty_AUHostIdentifier](audiotoolbox/kaudiounitproperty_auhostidentifier.md)
- [kAudioUnitProperty_BypassEffect](audiotoolbox/kaudiounitproperty_bypasseffect.md)
- [kAudioUnitProperty_ClassInfo](audiotoolbox/kaudiounitproperty_classinfo.md)
- [kAudioUnitProperty_ClassInfoFromDocument](audiotoolbox/kaudiounitproperty_classinfofromdocument.md)
- [kAudioUnitProperty_CocoaUI](audiotoolbox/kaudiounitproperty_cocoaui.md)
- [kAudioUnitProperty_ContextName](audiotoolbox/kaudiounitproperty_contextname.md)
- [kAudioUnitProperty_CPULoad](audiotoolbox/kaudiounitproperty_cpuload.md)
- [kAudioUnitProperty_DependentParameters](audiotoolbox/kaudiounitproperty_dependentparameters.md)
- [kAudioUnitProperty_ElementName](audiotoolbox/kaudiounitproperty_elementname.md)
- [kAudioUnitProperty_FactoryPresets](audiotoolbox/kaudiounitproperty_factorypresets.md)
- [kAudioUnitProperty_FastDispatch](audiotoolbox/kaudiounitproperty_fastdispatch.md)