如何在 Swift 2 / AVPlayer 中恢复背景音频？

Question

我正在学习 Swift 作为我的第一门编程语言。

在中断（例如通话）后，我努力恢复背景音频播放数小时

会发生什么：

1. 当应用程序进入后台时音频继续播放（有效）
2. 当被通话中断时，获取开始中断通知 （作品）
3. 通话结束时，获取中断通知 结束（工作）
4. 继续播放音频（不起作用 - 什么也听不见）

非常感谢任何帮助！谢谢

注意事项：

1. 该应用程序已注册背景音频并在中断前正常播放
2. 我尝试过有和没有时间延迟来恢复播放 - 都不起作用

代码：

import UIKit
import AVFoundation

var player: AVQueuePlayer!

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        do {
            try AVAudioSession.sharedInstance().setCategory(AVAudioSessionCategoryPlayback)
            try AVAudioSession.sharedInstance().setActive(true, withOptions: .NotifyOthersOnDeactivation)
        } catch { }
        let songNames = ["music"]
        let songs = songNames.map { AVPlayerItem(URL:
            NSBundle.mainBundle().URLForResource($0, withExtension: "mp3")!) }
        player = AVQueuePlayer(items: songs)

        let theSession = AVAudioSession.sharedInstance()
        NSNotificationCenter.defaultCenter().addObserver(self,
            selector:"playInterrupt:",
            name:AVAudioSessionInterruptionNotification,
            object: theSession)

        player.play()
    }

    func playInterrupt(notification: NSNotification) {

        if notification.name == AVAudioSessionInterruptionNotification
            && notification.userInfo != nil {

            var info = notification.userInfo!
            var intValue: UInt = 0
            (info[AVAudioSessionInterruptionTypeKey] as! NSValue).getValue(&intValue)
            if let type = AVAudioSessionInterruptionType(rawValue: intValue) {
                switch type {
                case .Began:
                    print("aaaaarrrrgggg you stole me")
                    player.pause()

                case .Ended:
                    let timer = NSTimer.scheduledTimerWithTimeInterval(3, target: self, selector: "resumeNow:", userInfo: nil, repeats: false)
                }
            }
        }
    }
    func resumeNow(timer : NSTimer) {
        player.play()
        print("attempted restart")
    }
}

Answer 1

终于明白了！

解决方案：通过将 setCategory 行更改为添加 mixable 选项：

AVAudioSession.sharedInstance().setCategory(AVAudioSessionCategoryPlayback,
                                            withOptions: .mixWithOthers )

Answer 2

我写了这样的代码并成功恢复了电话结束时的音频。我基于 Xcode 6.4 构建并在我的 iPhone 4S 上运行该应用程序。

var player: AVQueuePlayer! = nil

override func viewDidLoad()
{
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.
}

override func viewDidAppear(animated: Bool)
{
    super.viewDidAppear(true)

    var song = AVPlayerItem(URL: NSBundle.mainBundle().URLForResource("AlmostAYearAgo", withExtension: "mp3")!)
    player = AVQueuePlayer(items: [song])

    let theSession = AVAudioSession.sharedInstance()

    NSNotificationCenter.defaultCenter().addObserver(self, selector: "playInterrupt:", name: AVAudioSessionInterruptionNotification, object: theSession)

    player.play()
}

override func didReceiveMemoryWarning()
{
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}

func playInterrupt(notification: NSNotification)
{
    if notification.name == AVAudioSessionInterruptionNotification && notification.userInfo != nil
    {
        var info = notification.userInfo!
        var intValue: UInt = 0

        (info[AVAudioSessionInterruptionTypeKey] as! NSValue).getValue(&intValue)

        if let type = AVAudioSessionInterruptionType(rawValue: intValue)
        {
            switch type
            {
            case .Began:
                print("aaaaarrrrgggg you stole me")
                player.pause()
            case .Ended:
                let timer = NSTimer.scheduledTimerWithTimeInterval(3, target: self, selector: "resumeNow:", userInfo: nil, repeats: false)
            }
        }
    }
}

func resumeNow(timer : NSTimer)
{
    player.play()
    print("attempted restart")
}

Answer 3

结束中断后我重新加载播放器解决问题：

    func interruptionNotification(_ notification: Notification) {
    guard let type = notification.userInfo?[AVAudioSessionInterruptionTypeKey] as? UInt,
      let interruption = AVAudioSessionInterruptionType(rawValue: type) else {
        return
    }
    if interruption == .ended && playerWasPlayingBeforeInterruption {
      player.replaceCurrentItem(with: AVPlayerItem(url: radioStation.url))
      play()
    }
  }

Answer 4

对我来说，它增加了解决问题的延迟：

@objc func handleInterruption(_ notification: Notification) {
    // audio interuption - restart audio player for any type (began or ended) to make sure it keeps going
    guard let type = notification.userInfo?[AVAudioSessionInterruptionTypeKey] as? UInt,
        let interruption = AVAudioSession.InterruptionType(rawValue: type) else {
            NSLog("*** Incorrect notification format")
            return
    }

    if interruption == .began {
        NSLog("audio interruption: began")
    } else if interruption == .ended {
        NSLog("audio interruption: ended")
        if isRunning {
            // Sadly this lengthy delay hack is necessary, otherwise sounds won't play :(
            DispatchQueue.main.asyncAfter(deadline: .now() + 3.0) {
                self.start() // sets up the audio session, connects nodes, starts the engine, plays the player, and sets isRunning to true
            }
        }
    }
}

而且延迟确实需要这么长。 2s 没用。

Answer 5

Simon，请绝对确认。我花了2天时间寻找它！如果你只使用：

AVAudioSession.sharedInstance().setCategory(AVAudioSessionCategoryPlayback) 那么不管你做什么，如果你使用它，你的播放器将不会继续播放音频：

AVAudioSession.sharedInstance().setCategory(AVAudioSessionCategoryPlayback, withOptions: AVAudioSessionCategoryOptions.MixWithOthers)

然后它就像完美一样工作，并且在应用程序处于后台时接到电话后会恢复。

谢谢！