The following properties return Core Foundation objects:

• kAudioUnitProperty_ClassInfo - Returns a CFDictionaryRef.

• kAudioUnitProperty_ParameterValueStrings - Returns a CFArrayRef.

• kAudioUnitProperty_FactoryPresets - Returns a CFArrayRef.

• kAudioUnitProperty_ElementName - Returns a CFStringRef.

• kAudioUnitOfflineProperty_PreflightName - Returns a CFStringRef.

• kMusicDeviceProperty_BankName - Returns a CFStringRef.

The following properties return Core Foundation objects embedded as fields in C structures:

• kAudioUnitProperty_PresentPreset - Returns an AUPreset, where presetName is a CFStringRef containing the preset name.

• kAudioUnitProperty_ParameterStringFromValue - Returns a AudioUnitParameterStringFromValue struct where outString is a CFStringRef (may be NULL).

• kAudioUnitProperty_ParameterIDName - Returns a AudioUnitParameterNameInfo struct where outName is a CFStringRef.

• kAudioUnitProperty_ParameterClumpName - Returns a AudioUnitParameterNameInfo struct where outName is a CFStringRef.

• kAudioUnitProperty_CocoaUI - Returns a AudioUnitCocoaViewInfo struct where the CFStringRef class name(s) are returned in the mCocoaAUViewClass field.

The number of class names in the mCocoaAUViewClass field can be found by using the following code. dataSize is the maximum size of the property returned by calling AudioUnitGetPropertyInfo for the kAudioUnitProperty_CocoaUI property.

UInt32 numberOfClasses = (dataSize - sizeof(CFURLRef)) / sizeof(CFStringRef);

Handling Parameter Names

Ownership is based on the kAudioUnitParameterFlag_CFNameRelease flag. This flag is normally always set.

• kAudioUnitProperty_ParameterInfo - Returns a AudioUnitParameterInfo struct. Only release unitName and cfNameString CFStringRefs if the kAudioUnitParameterFlag_CFNameRelease flag is set. See Listing 1.

The Audio Unit Host should check for this flag and if set, should release the audio unit parameter name when it is done using it. If this flag is not set, the Host can assume that the Audio Unit will release its parameter names.

Listing 1  Illustrating use of kAudioUnitParameterFlag_CFNameRelease.

AudioUnitParameterInfo auinfo;
UInt32 propertySize = sizeof(AudioUnitParameterInfo);
OSStatus err = AudioUnitGetProperty(mAudioUnit,
                                    kAudioUnitProperty_ParameterInfo,
                                    mScope,
                                    mParameterID,
                                    &auinfo,
                                    &propertySize);
if (err) { // handle error };

... 

if (auinfo.flags & kAudioUnitParameterFlag_CFNameRelease) {
    if (auinfo.flags & kAudioUnitParameterFlag_HasCFNameString && auinfo.cfNameString != NULL)
        CFRelease(auinfo.cfNameString);
    if (auinfo.unit == kAudioUnitParameterUnit_CustomUnit && auinfo.unitName != NULL)
        CFRelease(auinfo.unitName);
}