Playground AVPlayer playing remote mp3 with with sounds played on top of that file

AudioPlayer.swift

import AVFoundation
import PlaygroundSupport

PlaygroundPage.current.needsIndefiniteExecution = true

class AudioPlayer {
    var topAudioFiles: [AVAudioFile] = []
    var engine:AVAudioEngine
    var topAudioAudioNodes = [AVAudioPlayerNode]()
    var mixer: AVAudioMixerNode
    var timer: Timer!
    var urls: [URL] = []
    var player: AVPlayer!
    var times = [NSValue]()
    var delays = [UInt64]()
    
    init (_ url: URL, urls: [URL] = []) {
        self.urls = urls
        topAudioFiles = urls.map { try! AVAudioFile(forReading: $0) }

        player = AVPlayer(url: url)
        
        engine = AVAudioEngine()
        mixer = AVAudioMixerNode()
        
        engine.attach(mixer)
        engine.connect(mixer, to: engine.outputNode, format: nil)
        
        initTimeOffsets()
        initTopAudioNodes()
        try! engine.start()
    }
    
    // play beeps every 1 bar @ 124 bpm (1936ms offset)
    func initTimeOffsets() {
        for i in 1...50 {
            let t = Double(1936 * i) / 1000.0
            times += [NSValue(time: CMTime(seconds: t, preferredTimescale: 600))]
        }
        for i in 1...100 {
            delays += [UInt64(i * 1936 / 1000 * 44100)]
        }
    }
    
    func initTopAudioNodes() {
        for _ in topAudioFiles {
            topAudioAudioNodes += [AVAudioPlayerNode()]
        }
        for node in topAudioAudioNodes {
            engine.attach(node)
            engine.connect(node, to: mixer, format: nil)
        }
    }
    
    func playWithAudioPlayerAndNodes() {
        player.play()
        var i = 1
        
        player.addBoundaryTimeObserver(forTimes: times, queue: nil) {
            let index = i % self.topAudioAudioNodes.count
            let node = self.topAudioAudioNodes[index]
            node.scheduleFile(self.topAudioFiles[index], at: nil, completionHandler: nil)
            node.play()
            i += 1
        }
    }
}

let bundle = Bundle.main
let beepLow = bundle.url(forResource: "beeplow", withExtension: "wav")!
let beepMid = bundle.url(forResource: "beepmid", withExtension: "wav")!
let backgroundAudio = URL(string: "https://www.xxxx.com/xxxx/mp3/xxxx-xxxx-1.mp3")!
let audioPlayer = AudioPlayer(backgroundAudio, urls: [beepLow, beepMid])

audioPlayer.playWithAudioPlayerAndNodes()