connectAudioUnitWithPlayer() connecting host view controller with audio unit plugin

ViewController.swift

private func connectAudioUnitWithPlayer() {
        var componentDescription = AudioComponentDescription()
        componentDescription.componentType = kAudioUnitType_Effect
        // used https://codebeautify.org/string-hex-converter to convert strings to fourCC hex
        componentDescription.componentSubType = 0x44656d6f // "Demo"
        componentDescription.componentManufacturer = 0x44656d6f // "Demo"
        componentDescription.componentFlags = 0
        componentDescription.componentFlagsMask = 0
        
        AUAudioUnit.registerSubclass(VolumePluginAudioUnit.self, as: componentDescription, name: "demo: VolumePlugin", version: UInt32.max)
        audioPlayer.selectAudioUnitWithComponentDescription(componentDescription) {
            guard let audioUnit = self.audioPlayer.audioUnit as? VolumePluginAudioUnit else {
                fatalError("playEngine.testAudioUnit nil or cast failed")
            }
            self.pluginVC.audioUnit = audioUnit
        }
    }