Change BPM in real time with AVAudioEngine using Swift - swift

Question

Hello I am trying to implement simple audio app using AVAudioEngine, which plays short wav audio files in a loop at some bpm, that can be changed in real time (by slider or something).
Current solution logic:
set bpm=60
create audioFile from sample.wav
calculate bufferSize: AVAudioFrameCount(audioFile.processingFormat.sampleRate * 60 / Double(bpm))
set bufferSize to audioBuffer
load file audioFile into audioBuffer.
schedule audioBuffer to play
This solution works, but the issue is - if I want to change bpm I need to recreate buffer with different bufferSize, so it will not be in real time, since I need to stop player and reschedule buffer with different bufferSize.
Any thoughts how it can be done ?
Thanks in advance !
Code (main part):
var bpm:Float = 30
let engine = AVAudioEngine()
var player = AVAudioPlayerNode()
var audioBuffer: AVAudioPCMBuffer?
var audioFile: AVAudioFile?
override func viewDidLoad() {
super.viewDidLoad()
audioFile = loadfile(from: "sound.wav")
audioBuffer = tickBuffer(audioFile: audioFile!)
engine.attach(player)
engine.connect(player, to: engine.mainMixerNode, format: audioFile?.processingFormat)
do {
engine.prepare()
try engine.start()
} catch {
print(error)
}
}
private func loadfile(from fileName: String) -> AVAudioFile? {
let path = Bundle.main.path(forResource: fileName, ofType: nil)!
let url = URL(fileURLWithPath: path)
do {
let audioFile = try AVAudioFile(forReading: url)
return audioFile
} catch {
print("Error loading buffer1 \(error)")
}
return nil
}
func tickBuffer(audioFile: AVAudioFile) -> AVAudioPCMBuffer {
let periodLength = AVAudioFrameCount(audioFile.processingFormat.sampleRate * 60 / Double(bpm))
let buffer = AVAudioPCMBuffer(pcmFormat: audioFile.processingFormat, frameCapacity: periodLength)!
try! audioFile.read(into: buffer)
buffer.frameLength = periodLength
return buffer
}
func play() {
player.scheduleBuffer(audioBuffer, at: nil, options: .loops, completionHandler: nil)
player.play()
}
func stop() {
player.stop()
}