How to continuously record Audio and play Audio from same file in Swift?

Question

I want to create something like a hearing aid app, where once i hit a the "startRecording" UIButton, it continuously records what I'm saying, and simultaneously plays it back to me at the same instant, in my earphones. It's basically to help people with hearing disabilities to hear the sounds from the surrounding environment, better and louder through earphones.

I am trying to implement it using the AVAudioKit, with the AudioRecorder and AudioPlayer working together with the same filepath "filename", in a while loop.

I get the error for line: audioPlayer.delegate = self

Thread 1: Fatal error: Unexpectedly found nil while unwrapping an Optional value.

            @IBOutlet weak var startRecording: UIButton!

var recordingSession : AVAudioSession!
var audioRecorder : AVAudioRecorder!
var audioPlayer : AVAudioPlayer!
var fileNameString : String = "test.m4a"




@IBAction func buttonPressed(_ sender: Any) {

    print("button pressed")
    let filename = getDirectory().appendingPathComponent("\(fileNameString)")


    if audioRecorder == nil{ // DAF needs to be started



        let settings = [AVFormatIDKey: Int(kAudioFormatAppleLossless),
                        AVEncoderAudioQualityKey: AVAudioQuality.max.rawValue,
                        AVEncoderBitRateKey: 320000,
                        AVNumberOfChannelsKey: 1,
                        AVSampleRateKey: 12000.0] as [String : Any]

        do{

            audioRecorder = try AVAudioRecorder(url: filename, settings: settings)
            audioRecorder.delegate = self
            //audioRecorder.record()

            do{
                audioPlayer = try AVAudioPlayer(contentsOf: filename, fileTypeHint: nil)
            }
            catch let error{
                print("\(error)")
            }
            audioPlayer.delegate = self
            audioPlayer.prepareToPlay()

            while true {
                audioRecorder.record()
                sleep(1)
                audioPlayer.play()
            }

            //startRecording.setTitle("Stop ", for: .normal)


        } catch{

            print ("failed")

        }

    }
    else { // DAF started, needs to stop

        audioRecorder.stop()
        audioRecorder = nil

        startRecording.setTitle("Start", for: .normal)

        playRecording()


    }

Answer 1

AVAudioRecording to a file and reading from that file to play will result in too much latency for real-time audio, due to the API writing and reading files using fairly large blocks or buffers of samples.

A better iOS API is to use for your purpose is the Audio Unit API with the RemoteIO Audio Unit. Using the RemoteIO Audio Unit can result in very low latencies from microphone to speaker (or headset). This is a C callback API however, as Apple currently does not recommend using Swift inside a real-time audio context.