来自AVAudioFile的AVAsset的持续时间为0

Question

我正在尝试从麦克风录制音频+，然后将其与来自多个位置的视频相结合，以创建具有麦克风音频的单个视频。

使用AVCaptureDevice + AVCaptureSession有点不稳定，我想做语音识别，所以我转到用AVCaptureSession做视频捕获，我试着用AVAudioEngine做音频(因为我的理解是把SFSpeechRecognizer连接到AudioTap上很容易)

代码如下：

class AudioCaptureSession {

    var engine = AVAudioEngine()
    var outputFile : AVAudioFile!

    func initAudioEngine() {
        engine.stop()
        engine.reset()
        engine = AVAudioEngine()

        do {
            try AVAudioSession.sharedInstance().setCategory(AVAudioSessionCategoryPlayAndRecord)
            let ioBufferDur = 128.0/44100.0
            try AVAudioSession.sharedInstance().setPreferredIOBufferDuration(ioBufferDur)
        } catch {
            print("AVAudioSession setup error: \(error)")
        }
        let outputPath = NSTemporaryDirectory().appending(kTempAudioFilename)
        let outputFile = URL(fileURLWithPath: outputPath, isDirectory: false)
        if FileManager.default.fileExists(atPath: outputPath) {
            do {
                try FileManager.default.removeItem(at: outputFile)
            } catch {
                print("Filemanager can't delete the audio file: \(error)")
            }
        }
        do {
            print("Settings: \(engine.mainMixerNode.outputFormat(forBus: 0).settings)")
            try self.outputFile = AVAudioFile(forWriting: outputFile, settings: engine.mainMixerNode.outputFormat(forBus: 0).settings)
        } catch {
            print("Can't make file for writing: \(error)")
        }
        let input = engine.inputNode!
        let format = input.inputFormat(forBus: 0)
        engine.connect(input, to: engine.mainMixerNode, format: format)
        engine.prepare()
        try! engine.start()

    }

    func startRecord() {
        let mixer = engine.mainMixerNode
        let format = mixer.outputFormat(forBus: 0)

        mixer.installTap(onBus: 0, bufferSize: 1024, format: format) { (buffer: AVAudioPCMBuffer!, time: AVAudioTime!) -> Void in
            do {
                try self.outputFile.write(from: buffer)
            } catch {
                print("Can't write audio to file: \(error)")
            }
        }
    }

    func stopRecord() {
        print("Audio len: \(self.outputFile.length)")
        engine.mainMixerNode.removeTap(onBus: 0)
        do {
            let f = try AVAudioFile(forReading: outputFile.url)
            print("Length of reading file: \(f.length)")
            print("Pos: \(f.framePosition)")
        } catch {
            print("Error getting file for reading: \(error)")
        }
        let asset = AVAsset(url: outputFile.url)
        print("Stop recording asset duration: \(asset.duration)")

    }
}

启动+停止后的示例输出为：

Audio len: 105840
Length of reading file: 0
Stop recording asset: CMTime(value: 0, timescale: 44100, flags: __C.CMTimeFlags(rawValue: 1), epoch: 0)

所以你可以看到，outputFile知道它有N个单位的长度，但是如果我打开一个文件读取，它认为它是0，并且AVAsset也认为它有0个持续时间。我想知道这个文件是不是没有保存？还是别的什么？我完全不知所措，因为我所看到的一切都是“生成一个AVAudioFile，file.write(缓冲区)，使用文件”，这显然是不起作用的。我必须导出它吗？还是别的什么？

Answer 1

AVAudioFile没有显式的close，所以当您完成对它的写入时，需要通过设置self.outputFile = nil让它超出作用域。