Loop mp3 with AVAudio

Question

I try to loop an mp3 file, where I can change its pitch while playing. I can change the pitch but I cannot loop the file. This is my code:

import AVKit

class ViewController: UIViewController {

    @IBOutlet weak var speedSlider: UISlider!
    @IBOutlet weak var speedLabel: UILabel!
    let pitchControl = AVAudioUnitTimePitch()
    let engine = AVAudioEngine()
    
    override func viewDidLoad(){
        super.viewDidLoad()
        do{ try playSound(soundName: "audiSound1")} catch{}
    }

    @IBAction func speedSlided(_ sender: Any) {
        pitchControl.pitch = speedSlider.value
        speedLabel.text = String(speedSlider.value)
    }
    
    func playSound(soundName: String) throws{
        guard let url = Bundle.main.url(forResource: soundName, withExtension: "mp3") else { return }
        let file = try AVAudioFile(forReading: url)
        let audioPlayer = AVAudioPlayerNode()
        engine.attach(audioPlayer)
        engine.attach(pitchControl)
        engine.connect(audioPlayer, to: pitchControl, format: nil)
        engine.connect(pitchControl, to: engine.mainMixerNode, format: nil)
        audioPlayer.scheduleFile(try! AVAudioFile(forReading: url), at: nil)
        try engine.start()
        audioPlayer.play()
    }
}

To make it loop, I tried using an AVAudioPCMBuffer(), see:

import AVKit

class ViewController: UIViewController {

    @IBOutlet weak var speedSlider: UISlider!
    @IBOutlet weak var speedLabel: UILabel!
    let pitchControl = AVAudioUnitTimePitch()
    let engine = AVAudioEngine()
    
    override func viewDidLoad(){
        super.viewDidLoad()
        do{ try playSound(soundName: "audiSound1")} catch{}
    }

    @IBAction func speedSlided(_ sender: Any) {
        pitchControl.pitch = speedSlider.value
        speedLabel.text = String(speedSlider.value)
    }
    
    func playSound(soundName: String) throws{
        guard let url = Bundle.main.url(forResource: soundName, withExtension: "mp3") else { return }
        let file = try AVAudioFile(forReading: url)
        let audioPlayer = AVAudioPlayerNode()
        
        //New:
        let audioFileBuffer = AVAudioPCMBuffer(pcmFormat: file.fileFormat, frameCapacity: AVAudioFrameCount(file.length))
        try? file.read(into: audioFileBuffer!)

        engine.attach(audioPlayer)
        engine.attach(pitchControl)
        engine.connect(audioPlayer, to: pitchControl, format: nil)
        engine.connect(pitchControl, to: engine.mainMixerNode, format: nil)
        audioPlayer.scheduleBuffer(audioFileBuffer!,at: nil, options: .loops, completionHandler: nil) //Changed
        try engine.start()
        audioPlayer.play()
    }
}

But when I run the project, it gives me a Thread 1: "required condition is false: isPCMFormat" Error :/ The exact error message is:

2021-04-06 20:31:51.824454+0200 avas[67546:8825321] [avae] AVAEInternal.h:76 required condition is false: [AVAudioBuffer.mm:175:-[AVAudioPCMBuffer initWithPCMFormat:frameCapacity:]: (isPCMFormat)] 2021-04-06 20:31:51.832637+0200 avas[67546:8825321] *** Terminating app due to uncaught exception 'com.apple.coreaudio.avfaudio', reason: 'required condition is false: isPCMFormat'

I have no idea how I can make it loop in another (working) way. Can someone help me? :)

Thank you so much!

score 0 · Answer 1 · answered Apr 06 '21 at 19:42

This works:

import AVKit

class ViewController: UIViewController {

    @IBOutlet weak var speedSlider: UISlider!
    @IBOutlet weak var speedLabel: UILabel!
    let pitchControl = AVAudioUnitTimePitch()
    let engine = AVAudioEngine()
    
    override func viewDidLoad(){
        super.viewDidLoad()
        do{ try playSound(soundName: "audiSound1")} catch{}
    }

    @IBAction func speedSlided(_ sender: Any) {
        pitchControl.pitch = speedSlider.value
        speedLabel.text = String(speedSlider.value)
    }
    
    func playSound(soundName: String) throws{
        guard let url = Bundle.main.url(forResource: soundName, withExtension: "mp3") else { return }
        let file = try AVAudioFile(forReading: url)
        let audioPlayer = AVAudioPlayerNode()
        let audioFormat = file.processingFormat
        let audioFrameCount = UInt32(file.length)
        let audioFileBuffer = AVAudioPCMBuffer(pcmFormat: audioFormat, frameCapacity: audioFrameCount)
        
        try! file.read(into: audioFileBuffer!)
        let mainMixer = engine.mainMixerNode
        
        engine.attach(audioPlayer)
        engine.attach(pitchControl)
        engine.connect(audioPlayer, to: mainMixer, format: audioFileBuffer?.format)
        engine.connect(audioPlayer, to: pitchControl, format:audioFileBuffer?.format)
        engine.connect(pitchControl, to: engine.mainMixerNode, format: nil)
        
        try engine.start()
        audioPlayer.play()
        audioPlayer.scheduleBuffer(audioFileBuffer!, at: nil, options: .loops, completionHandler: nil)
    }
}

Loop mp3 with AVAudio

1 Answers1