AVAudioFile init 在模拟器上工作但在设备上崩溃

Question

我想构建一个 iOS 应用（使用 Swift 3 和 Xcode 8.2.1），从 iPhone 的麦克风记录并将记录保存到 .caf 文件。

---

首先，我在我的项目的 Info.plist 文件中添加了以下几行：

<key>NSMicrophoneUsageDescription</key>
<string>Some description to explain why access is required</string>

然后，我创建了一个简单的UIViewController，它设置了一个AVAudioEngine，并在点击Record 和Stop 按钮时安装/删除音频水龙头。

ViewController.swift

import UIKit
import AVFoundation

class ViewController: UIViewController {

    var engine = AVAudioEngine()
    var file: AVAudioFile?
    var player = AVAudioPlayerNode()

    override func viewDidLoad() {
        super.viewDidLoad()

        guard let url = urlFor(filename: "test.caf") else { return }
        do {
            file = try AVAudioFile(forWriting: url, settings: engine.inputNode!.inputFormat(forBus: 0).settings, commonFormat: engine.inputNode!.inputFormat(forBus: 0).commonFormat, interleaved: false)
        } catch {
            print("Error: \(error)")
        }

        engine.attach(player)
        engine.connect(player, to: engine.mainMixerNode, format: engine.mainMixerNode.outputFormat(forBus: 0))

        do {
            try engine.start()
        } catch {
            print("Error: \(error)")
        }
    }

    @IBAction func record(sender: AnyObject) {
        engine.inputNode?.installTap(onBus: 0, bufferSize: 1024, format: engine.mainMixerNode.outputFormat(forBus: 0)) { (buffer, time) -> Void in
            do {
                try self.file?.write(from: buffer)
            } catch {
                print("Error: \(error)")
            }
        }
    }

    @IBAction func stop(sender: AnyObject) {
        engine.inputNode?.removeTap(onBus: 0)
        // Print the url of the saved file
        let urls = FileManager.default.urls(for: .applicationSupportDirectory, in: .userDomainMask)
        print(urls[urls.endIndex - 1])
    }

    func urlFor(filename: String) -> URL? {
        // Get url of saved file
        if let dir = NSSearchPathForDirectoriesInDomains(FileManager.SearchPathDirectory.documentDirectory, FileManager.SearchPathDomainMask.allDomainsMask, true).first {
            let path = dir.appending(filename)
            return URL(fileURLWithPath: path)
        }
        return nil
    }

}

---

该应用程序在模拟器上运行良好：我可以录制我的声音，获取录制文件的 url 并测试我的声音是否已正确录制。但是，该应用程序在我在设备上启动后立即崩溃（在 iOS 10.2.1 上使用 iPhone 6s 进行了测试）。控制台给了我以下日志：

2017-02-08 17:09:14.330151 AudioEngineSimpleApp[7100:2659416] Audio files cannot be non-interleaved. Ignoring setting AVLinearPCMIsNonInterleaved YES.
2017-02-08 17:09:14.333715 AudioEngineSimpleApp[7100:2659416] [central] 54:   ERROR:    [0x1b7440c40] >avae> AVAudioFile.mm:160: AVAudioFileImpl: error -54
2017-02-08 17:09:14.333796 AudioEngineSimpleApp[7100:2659416] [central] 54:   ERROR:    [0x1b7440c40] >avae> AVAudioFile.mm:122: ReadMagicCookie: error -50
2017-02-08 17:09:14.334369 AudioEngineSimpleApp[7100:2659416] *** Terminating app due to uncaught exception 'com.apple.coreaudio.avfaudio', reason: 'error -50'

这个问题似乎与 Stack Overflow 线程 AVAudioPlayer working on Simulator but not on Real Device 有关，但我不知道如何将其响应实现到我自己的代码中以解决我的问题。

Answer 1

我已经重构了我的代码，并用以下 url 属性替换了旧的 urlFor(filename: String) -> URL? 方法：

let url = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first!.appendingPathComponent("test.caf")

---

因此，以下代码在设备上正常工作：

import UIKit
import AVFoundation

class ViewController: UIViewController {

    @IBOutlet weak var recordButton: UIButton!
    let url = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first!.appendingPathComponent("test.caf")
    //let url = URL(fileURLWithPath: NSTemporaryDirectory().appending("test.caf")) also works
    var engine = AVAudioEngine()

    override func viewDidLoad() {
        super.viewDidLoad()

        recordButton.setTitle("Record", for: .normal)

        let file: AVAudioFile
        do {
            file = try AVAudioFile(forWriting: url, settings: engine.inputNode!.outputFormat(forBus: 0).settings)
        } catch {
            print("Error: \(error)")
            return
        }

        engine.inputNode?.installTap(onBus: 0, bufferSize: 1024, format: engine.inputNode!.outputFormat(forBus: 0)) { (buffer, time) -> Void in
            do {
                try file.write(from: buffer)
            } catch {
                print("Error: \(error)")
            }
        }
    }

    @IBAction func toggleAction(_ sender: AnyObject) {
        engine.isRunning ? stopRecording() : startRecording()
    }

    func startRecording() {
        do {
            // Start engine
            try engine.start()

            // Toggle button title
            recordButton.setTitle("Stop", for: .normal)
        } catch {
            print("Error: \(error)")
        }
    }

    func stopRecording() {
        // Stop engine
        engine.stop()

        // Toggle button title
        recordButton.setTitle("Record", for: .normal)

        print(url)
    }

}