如何监控设备的音频输出以判断声音是否来自扬声器/耳机插孔？

Question

我需要在设备开始输出音频时立即启动操作。我正在使用 AVPlayer 并正在从 Parse 流式传输音频文件。使用等待 (AVPlayer.currentTime() != nil) 和 (AVPlayer.rate > 0) 等其他方法不够准确，我需要确切知道从设备输出音频的时间。我尝试使用 AVAudioEngine，然后附加一个具有 AVAudioNodeBus 的 AVAudioNode，但我无法让它工作。任何建议或技术都会非常好，谢谢！

这是我的 AudioEngine 代码。我在实例级别实例化 AudioEngine。创建standardFormat 时，我不知道standardFormatWithSampleRate 或通道块使用什么。当我尝试 installTapOnBus 时，我不知道该块使用什么，所以我输入了 nil，但这也会触发错误。任何帮助将不胜感激，我对 iOS 开发人员非常陌生，并且已多次阅读 Apple 的文档，但我无法完全理解它，也无法在网上找到任何最近的示例。

class TableViewController: UITableViewController, AVAudioPlayerDelegate {

var iDArray = [String]()
var NameArray = [String]()


var durationInSeconds = Double()

var currentSong = String()




override func viewDidLoad() {
    super.viewDidLoad()



    let ObjectIDQuery = PFQuery(className: "Songs")
    ObjectIDQuery.findObjectsInBackgroundWithBlock {
        (objectsArray: [PFObject]?, error: NSError?) -> Void in

        //objectsArray!.count != 0
        var objectIDs = objectsArray!

        for i in 0...objectIDs.count-1 {
                self.iDArray.append(objectIDs[i].valueForKey("objectId") as! String)
                self.NameArray.append(objectIDs[i].valueForKey("SongName") as! String)

                self.tableView.reloadData()
            }

    }

    do {
        try AVAudioSession.sharedInstance().setCategory(AVAudioSessionCategoryPlayback)
        print("AVAudioSession Category Playback OK")
        do {
            try AVAudioSession.sharedInstance().setActive(true)
            print("AVAudioSession is Active")
        } catch let error as NSError {
            print(error.localizedDescription)
        }
    } catch let error as NSError {
        print(error.localizedDescription)
    }



}

func grabSong () {


    let songQuery = PFQuery(className: "Songs")
    songQuery.getObjectInBackgroundWithId(iDArray[SelectedSongNumber], block: {
        (object: PFObject?, error : NSError?) -> Void in


        if let audioFile = object?["SongFile"] as? PFFile {
            let audioFileUrlString: String = audioFile.url!
            let audioFileUrl = NSURL(string: audioFileUrlString)!


            AudioPlayer = AVPlayer(URL: audioFileUrl)
            AudioPlayer.play()

    })

}

func audioFunction() {

    var audioPlayerNode = AVAudioNode()
    var audioBus = AVAudioNodeBus()


    var standardFormat = AVAudioFormat(standardFormatWithSampleRate: <#T##Double#>, channels: <#T##AVAudioChannelCount#>)


    AudioEngine.attachNode(audioPlayerNode)

    audioPlayerNode.outputFormatForBus(audioBus)

    audioPlayerNode.installTapOnBus(audioBus, bufferSize: 100, format: standardFormat, block: nil)

    if AudioEngine.running == true {
        print("the audio engine is running")
    } else {
        print("the audio engine is NOTTT running")
    }

}


func attachNode(audioNode : AVAudioNode) {
    AudioEngine.attachNode(audioNode)

    AudioEngine.outputNode
    print(AudioEngine.outputNode.description)

    if AudioEngine.running == true {
        print("the audio engine is running")
    } else {
        print("the audio engine is NOTTT running")
    }
}

override func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {

    return iDArray.count
}


override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
    let cell = tableView.dequeueReusableCellWithIdentifier("Cell")
    cell?.textLabel!.text = NameArray[indexPath.row]

    return cell!
}



override func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {

   SelectedSongNumber = indexPath.row
    grabSong()
}

}

我应该改用 AVAudioSession 吗？还是 AVCaptureSession？

Answer 1

我会在AVPlayer 上使用音频点击来了解音频何时实际播放/即将播放。基本上，您会在音频播放到扬声器/耳机插孔之前收到音频点击回调。

一些复杂情况：我不确定如何获取某些流媒体类型（pls、icecast）的 AVAsset 曲目，但远程（和本地）mp3 文件可以正常工作。

var player: AVPlayer?

func doit() {
    let url = NSURL(string: "URL TO YOUR POSSIBLY REMOTE AUDIO FILE")!
    let asset = AVURLAsset(URL:url)
    let playerItem = AVPlayerItem(asset: asset)

    let tapProcess: @convention(c) (MTAudioProcessingTap, CMItemCount, MTAudioProcessingTapFlags, UnsafeMutablePointer<AudioBufferList>, UnsafeMutablePointer<CMItemCount>, UnsafeMutablePointer<MTAudioProcessingTapFlags>) -> Void = {
        (tap, numberFrames, flags, bufferListInOut, numberFramesOut, flagsOut) -> Void in

        // Audio coming out!
        let status = MTAudioProcessingTapGetSourceAudio(tap, numberFrames, bufferListInOut, flagsOut, nil, numberFramesOut)
        print("get audio: \(status)\n")
    }

    var callbacks = MTAudioProcessingTapCallbacks(
        version: kMTAudioProcessingTapCallbacksVersion_0,
        clientInfo: UnsafeMutablePointer(Unmanaged.passUnretained(self).toOpaque()),
        `init`: nil,
        finalize: nil,
        prepare: nil,
        unprepare: nil,
        process: tapProcess)

    var tap: Unmanaged<MTAudioProcessingTap>?
    let err = MTAudioProcessingTapCreate(kCFAllocatorDefault, &callbacks, kMTAudioProcessingTapCreationFlag_PostEffects, &tap)

    if err != noErr {
        // TODO: something
    }

    let audioTrack = playerItem.asset.tracksWithMediaType(AVMediaTypeAudio).first!
    let inputParams = AVMutableAudioMixInputParameters(track: audioTrack)
    inputParams.audioTapProcessor = tap?.takeUnretainedValue()

    let audioMix = AVMutableAudioMix()
    audioMix.inputParameters = [inputParams]

    playerItem.audioMix = audioMix

    player = AVPlayer(playerItem: playerItem)
    player?.play()
}