Swift: Audioaufnahmen mit AVAudioRecorder

class AudioViewController : UIViewController, AVAudioRecorderDelegate
{
    // [...]
 
    var audioRecorder: AVAudioRecorder!
     
    func initAudioRecorder()
    {
        let settings: [String : Any] = [
            AVSampleRateKey: 16000.0,
            AVFormatIDKey: kAudioFormatMPEG4AAC,
            AVNumberOfChannelsKey: 1,
            AVEncoderAudioQualityKey: AVAudioQuality.low.rawValue
        ]
         
        let audioSession = AVAudioSession.sharedInstance()
        do {
            try audioSession.setCategory(AVAudioSessionCategoryRecord)
            try audioRecorder = AVAudioRecorder(url: getFileurl()!, settings: settings)
            try audioSession.setActive(true)
        }
        catch let error as NSError {
            print("AVAudioRecorder error: \(error.localizedDescription)")
        }
     
        audioRecorder.delegate = self
        audioRecorder.isMeteringEnabled = true
        audioRecorder.prepareToRecord()
         
        let displayLink:CADisplayLink = CADisplayLink(target: self, selector: #selector(updateMeters))
        displayLink.add(to: RunLoop.current, forMode: RunLoopMode.commonModes)
    }
     
    func updateMeters()
    {
        audioRecorder.updateMeters()
         
        if audioRecorder.isRecording
        {
            let time = NSInteger(audioRecorder.currentTime)
            // ...
        }
 
        // TOOD: do any updates e.g. for the UI (update displayed record time, ...)
    }
 
    @IBAction func startRecord(_ sender: AnyObject)
    {
        audioRecorder.record()
    }
 
    @IBAction func stopRecord(_ sender: AnyObject)
    {
        audioRecorder.stop()
    }
     
    func audioRecorderDidFinishRecording(_ recorder: AVAudioRecorder, successfully flag: Bool)
    {
        // Add audio to attachments
        let audioData = try? Data(contentsOf: getFileurl()!)
        if audioData != nil
        {
            // TOOD: handle audio data
        }
    }
     
    func getFileurl() -> URL?
    {
        let fileManager = FileManager.default
        let urls = fileManager.urls(for: .documentDirectory, in: .userDomainMask)
        let documentDirectory = urls[0] as URL
        let audioURL = documentDirectory.appendingPathComponent("audio.m4a")
         
        return audioURL
    }
}