AUAudioUnit VoiceProcessingIO不在macOS上调用inputHandler

Question

我试图在Swift中使用新的AUAudioUnit API在iOS和macOS上使用VoiceProcessingIO单元，如下所示：

var description = AudioComponentDescription()
description.componentType = kAudioUnitType_Output
description.componentSubType = kAudioUnitSubType_VoiceProcessingIO
description.componentManufacturer = kAudioUnitManufacturer_Apple
description.componentFlags = 0
description.componentFlagsMask = 0

var vpio: AUAudioUnit
vpio = try! AUAudioUnit(componentDescription: description)

print("canPerformInput:", vpio.canPerformInput)
print("isInputEnabled:", vpio.isInputEnabled)
print("canPerformOutput:", vpio.canPerformOutput)
print("isOutputEnabled:", vpio.isOutputEnabled)
print("---")

vpio.isInputEnabled = true

vpio.inputHandler = { (actionFlags, timestamp, frameCount, inputBusNumber) in
    print("inputHandler called")
}

vpio.outputProvider = { (actionFlags, timestamp, frameCount, inputBusNumber, inputData) -> AUAudioUnitStatus in
    print("outputProvider called")
    return noErr
}

try! vpio.allocateRenderResources()
try! vpio.startHardware()

此代码适用于iOS（10.2），它调用inputHandler和outputProvider：

canPerformInput: true
isInputEnabled: false
canPerformOutput: true
isOutputEnabled: true
---
inputHandler called
outputProvider called
inputHandler called
outputProvider called
...

在macOS（10.12.2）上，只调用outputProvider：

canPerformInput: true
isInputEnabled: true
canPerformOutput: true
isOutputEnabled: true
---
outputProvider called
outputProvider called
outputProvider called
outputProvider called
...

观察：在iOS上，isInputEnabled默认设置为false，必须启用（第17行）才能调用inputHandler。在macOS上，默认情况下启用它，但不调用inputHandler。像上面那样明确设置isInputEnabled也不起作用。

当使用Apple's echoTouch sample code和suggested here by theanalogkid中使用的旧API（AudioUnit，AudioComponentInstanceNew，AudioUnitSetProperty，kAudioOutputUnitProperty_SetInputCallback等...）时，VPIO可以在macOS上正常工作（除非在macOS上你不能和不要＆＃ 39; t需要设置kAudioOutputUnitProperty_EnableIO）

我在这里做错了什么，或者这可能是苹果公司的一个错误？