如何开始在后台播放AVPlayer的音轨？

let audioSession = AVAudioSession.sharedInstance()
do {
    try audioSession.setCategory(.playback, mode: .default, options: [])
    try audioSession.setActive(true)
} catch {
    print("Failed to set audio session category.")
}

let audioURL = URL(string: "https://example.com/audio.mp3")!
let playerItem = AVPlayerItem(url: audioURL)
let player = AVPlayer(playerItem: playerItem)

func applicationDidEnterBackground(_ application: UIApplication) {
    player.play()
}

func remoteControlReceived(with event: UIEvent?) {
    if event?.type == .remoteControl {
        switch event!.subtype {
        case .remoteControlPlay:
            player.play()
        case .remoteControlPause:
            player.pause()
        case .remoteControlStop:
            player.pause()
            player.seek(to: CMTime.zero)
        default:
            break
        }
    }
}