当应用程序在后台时，iOS 12.4 AVAudioRecorder.record 返回 false

Question

首先，此错误仅在 iOS 上最新的 12.4 版本中出现。该问题不会在模拟器中发生，必须在设备上运行。问题是一旦应用程序进入后台，对 AVAudioRecorder 上的记录的调用将返回 false。在所有以前的 iOS 版本中，这不会发生。 info.plist 使用 NSMicrophoneUsageDescription 标记进行更新，应用程序的功能包括音频背景模式。

我写了一个小的 ViewController 来显示这个问题。重建步骤：

1) Update the info.plist file with the NSMicrophoneUsageDescription tag so that the app gets permission to use the microphone 2) Update the app capabilities to set Audio background mode 3) Run the application 4) Send the application to the background 5) The current recording will finish, but the call to start a new recording will fail.

class ViewController: UIViewController, AVAudioRecorderDelegate {
   var recordLabel: UILabel!
   var recordingSession: AVAudioSession!
   var audioRecorder: AVAudioRecorder!
   var count: Int = 0

   override func viewDidLoad() {
       super.viewDidLoad()

       recordingSession = AVAudioSession.sharedInstance()

       do {
           try recordingSession.setCategory(.playAndRecord, mode: .default)
           try recordingSession.setActive(true)
           recordingSession.requestRecordPermission() { [unowned self] allowed in
               DispatchQueue.main.async {
                   if allowed {
                       self.loadRecordingUI()
                   } else {
                       print("No permissions!!!")
                   }
               }
           }
       } catch {
           print("Exception in viewDidLoad!!!")
       }
   }

   func loadRecordingUI() {
       super.viewDidLoad()

       recordLabel = UILabel(frame: CGRect(x: 0, y: 0, width: 300, height: 21))
       recordLabel.center = CGPoint(x: 160, y: 285)
       recordLabel.textAlignment = .center
       recordLabel.text = "Waiting...."
       self.view.addSubview(recordLabel)

       setupRecorder()
       startRecording();
   }

   func setupRecorder() {
       let audioFilename = getDocumentsDirectory().appendingPathComponent("recording.m4a")

       let settings = [
           AVFormatIDKey: Int(kAudioFormatMPEG4AAC),
           AVSampleRateKey: 12000,
           AVNumberOfChannelsKey: 1,
           AVEncoderAudioQualityKey: AVAudioQuality.high.rawValue
       ]

       do {
           audioRecorder = try AVAudioRecorder(url: audioFilename, settings: settings)
           audioRecorder.delegate = self
       } catch {
           print("Exception thrown in setupRecorder")
       }
   }

   func startRecording() {
       count += 1

       let ret = audioRecorder.record(forDuration: 10)  //record for 10 seonds

       let txt = "Record returned " + ret.description + " for #\(count)"
       recordLabel.text = txt
       print(txt)
   }

   func getDocumentsDirectory() -> URL {
       let paths = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)
       return paths[0]
   }

   func audioRecorderDidFinishRecording(_ recorder: AVAudioRecorder, successfully flag: Bool) {
       startRecording()  //immediately start recording again
   }
}

由于设置了应用程序在后台录制的功能，我希望在 AVAudioRecorder 上录制的调用返回 true

Answer 1

我就此向 Apple 提交了反馈（audioRecorder.record() 在后台返回 false）并得到答案，这是一个新的隐私保护限制，即他们不会修复它。

“提到的行为是一种改变，但它是正确的行为，尝试在后台开始之前没有录制的音频录制（然后被电话或 Siri 打断）将不起作用（基本上是尝试开始从后台随机录制将不再起作用）。这是 12.4 中引入的新的隐私保护限制。”