os x: get default audio input device volume

audioInputVolume.swift

func getDefaultAudioInputVolume() -> Float32? {
        var audioVolumeAddr = AudioObjectPropertyAddress(
            mSelector: kAudioHardwareServiceDeviceProperty_VirtualMasterVolume,
            mScope: kAudioObjectPropertyScopeInput,
            mElement: kAudioObjectPropertyElementMaster
        )

        guard let audioInputDevice = getDefaultAudioInputDevice() else {
            return nil
        }

        var audioInputVolume: Float32 = 0
        var propertySize = UInt32(MemoryLayout.size(ofValue: audioInputVolume))

        let error = AudioObjectGetPropertyData(AudioObjectID(audioInputDevice),
                                               &audioVolumeAddr,
                                               0,
                                               nil,
                                               &propertySize,
                                               &audioInputVolume)

        if error != kAudioHardwareNoError {
            return nil
        }

        return audioInputVolume
    }