为什么 AVAudioPlayer 的 currentTime 和 duration 为零？答案

【问题标题】：why currentTime and duration of AVAudioPlayer are nil?为什么 AVAudioPlayer 的 currentTime 和 duration 为零？
【发布时间】：2019-03-13 09:03:38
【问题描述】：

为什么AVAudioPlayer的currentTime和duration都是nil？

最近在创建玩家时面临一个任务链接到 mp3 工作，检查但同时跟踪持续时间和当前时间为零我尝试将 AVAudioPlayer 更改为 AVPlayer，但我有同样的问题

我需要做什么来纠正这个问题？

也许我必须在阅读时间之前下载这个 mp3？

不过这个问题最好不用下载mp3来解决

import UIKit
import AVFoundation

class PlayerViewController: UIViewController {

//Instantiate the AVFoundation audio player class
var player: AVAudioPlayer?

//Timer for tracking the progress
var timer: Timer? = nil

@IBOutlet weak var bookCoverImageView: UIImageView!
@IBOutlet weak var timeSlider: CustomSlider!
@IBOutlet weak var timeFromStartLabel: UILabel!
@IBOutlet weak var remainingTimeLabel: UILabel!
@IBOutlet weak var previousButton: UIButton!
@IBOutlet weak var nextButton: UIButton!
@IBOutlet weak var playButton: UIButton!
@IBOutlet weak var bookNameLabel: UILabel!
@IBOutlet weak var authorNameLabel: UILabel!

override func viewDidLoad() {
    super.viewDidLoad()

    _ = Timer.scheduledTimer(timeInterval: 0.1, target: self, selector: #selector(updateSlider), userInfo: nil, repeats: true)

    do {
        //Set the path to the audio file (comes from the bundle)
        let path = URL(string: "https://firebasestorage.googleapis.com/v0/b/audio-summary-v3.appspot.com/o/%D0%92%D1%8B%D1%81%D1%82%D1%83%D0%BF%D0%BB%D0%B5%D0%BD%D0%B8%D0%B5%20%D0%B2%20%D1%81%D1%82%D0%B8%D0%BB%D0%B5%20TED%20-%20%D0%94%D0%B6%D0%B5%D1%80%D0%B5%D0%BC%D0%B8%20%D0%94%D0%BE%D0%BD%D0%BE%D0%B2%D0%B0%D0%BD.mp3?alt=media&token=58cae883-36b8-445f-8338-cc04cd518eee")

        //Unpacking the path string optional
        if let unpackedPath = path {

            try player = AVAudioPlayer(contentsOf: unpackedPath)
            timer = Timer.scheduledTimer(withTimeInterval: 1.0, repeats: true) { timer in

                self.timeFromStartLabel.text = String(format: "%d:%02d", Int(self.player!.currentTime) / 60, Int(self.player!.currentTime) % 60)
                self.remainingTimeLabel.text = String(format: "%d:%02d", Int(self.player!.duration - self.player!.currentTime) / 60, Int(self.player!.duration - self.player!.currentTime) % 60)
            }
            player!.play()
            timer!.fire()
        }

    } catch {
        print(error)
    }

    do {
        try AVAudioSession.sharedInstance().setCategory(.playback, mode: .default, options: [.mixWithOthers, .allowAirPlay])
        print("Playback OK")
        try AVAudioSession.sharedInstance().setActive(true)
        print("Session is Active")
    } catch {
        print(error)
    }

这里有错误

    timeSlider.maximumValue = Float(self.player!.duration)
}

@IBAction func playButtonTapped(_ sender: Any) {
    if player!.isPlaying {
        player?.stop()
        playButton.setImage(UIImage(named: "play_button"), for: .normal)
    }
    else {
        player?.play()
        playButton.setImage(UIImage(named: "stop_button"), for: .normal)
    }
}

@IBAction func timeSliderScrolling(_ sender: Any) {
    player?.stop()
    player?.currentTime = TimeInterval(timeSlider.value)
    player?.prepareToPlay()
    player?.play()
}

@objc func updateSlider() {

这里有错误

    timeSlider.value = Float(player!.currentTime)
}

}

【问题讨论】：

使用AVURLAsset和AVPlayerItem。
我需要如何使用它？也许你可以给我链接或其他东西来研究它？

标签： swift avaudioplayer audio-streaming

【解决方案1】：

在AVAudioPlayer 上使用AVPlayer，这样您就可以使用addPeriodicTimeObserver 观察当前的播放时间。

import UIKit
import AVFoundation

class ViewController: UIViewController {
    // MARK: - Variables
    var player: AVPlayer?

    @IBAction func playAudio(_ sender: UIBarButtonItem) {
        player?.play()
    }

    override func viewDidLoad() {
        super.viewDidLoad()

        guard let path = Bundle.main.path(forResource: "myAudio", ofType:"m4a") else {
            debugPrint("File not found")
            return
        }

        let audioURL = URL(fileURLWithPath: path)
        let playerItem = AVPlayerItem(url: audioURL)
        player = AVPlayer(playerItem: playerItem)

        player!.addPeriodicTimeObserver(forInterval: CMTimeMakeWithSeconds(1, preferredTimescale: 1), queue: DispatchQueue.main) { (CMTime) -> Void in
            if self.player!.currentItem?.status == .readyToPlay {
                let time : Float64 = CMTimeGetSeconds(self.player!.currentTime());
                print("Current play time: \(time)")
            }
        }
    }
}

【讨论】：