AVAssetWriterInput -黑色屏幕，46小时长

Question

我正在尝试使用一个AVCaptureSession并将其编码到mp4。这看起来应该很简单，我正在尝试编码一个960x540视频流，我并不担心这个问题的音频。

当我运行以下代码并使用Xcode从文档容器中抓取out2.mp4时，很快就会看到一个黑色屏幕，持续时间为46小时。至少决议看起来是对的。这是来自ffmpeg -i out2.mp4的输出

Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'out2.mp4':
  Metadata:
    major_brand     : mp42
    minor_version   : 1
    compatible_brands: mp41mp42isom
    creation_time   : 2015-11-18 01:25:55
  Duration: 46:43:04.21, start: 168178.671667, bitrate: 0 kb/s
    Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, smpte170m/bt709/bt709), 960x540, 1860 kb/s, 27.65 fps, 29.97 tbr, 600 tbn, 1200 tbc (default)
    Metadata:
      creation_time   : 2015-11-18 01:25:55
      handler_name    : Core Media Video

为什么我不能在这个场景中将示例缓冲区附加到AVAssetWriterInput中？

var videoInput: AVAssetWriterInput?
var assetWriter: AVAssetWriter?

override func viewDidLoad() {
    super.viewDidLoad()
    self.startStream()
    NSTimer.scheduledTimerWithTimeInterval(5, target: self, selector: "swapSegment", userInfo: nil, repeats: false)
}

func swapSegment() {
    assetWriter?.finishWritingWithCompletionHandler(){
        print("File written")
    }
    videoInput = nil
}

func pathForOutput() -> String {
    let urls = NSFileManager.defaultManager().URLsForDirectory(.DocumentDirectory, inDomains: .UserDomainMask)
    if let documentDirectory: NSURL = urls.first {
        let fileUrl = documentDirectory.URLByAppendingPathComponent("out1.mp4")
        return fileUrl.path!
    }
    return ""
}

func startStream() {
    assetWriter = try! AVAssetWriter(URL: NSURL(fileURLWithPath: self.pathForOutput()), fileType: AVFileTypeMPEG4)

    let videoSettings: [String: AnyObject] = [AVVideoCodecKey: AVVideoCodecH264, AVVideoWidthKey: 960, AVVideoHeightKey: 540]
    videoInput = AVAssetWriterInput(mediaType: AVMediaTypeVideo, outputSettings: videoSettings)
    videoInput!.expectsMediaDataInRealTime = true
    assetWriter?.addInput(videoInput!)
    assetWriter!.startWriting()
    assetWriter!.startSessionAtSourceTime(kCMTimeZero)

    let videoHelper = VideoHelper()
    videoHelper.delegate = self
    videoHelper.startSession()
}

func captureOutput(captureOutput: AVCaptureOutput!, didOutputSampleBuffer sampleBuffer: CMSampleBufferRef, fromConnection connection: AVCaptureConnection!) {
    if let videoOutput = captureOutput as? AVCaptureVideoDataOutput {
        videoInput?.appendSampleBuffer(sampleBuffer)
    }
}

Answer 1

也许您的演示时间与您的sourceTime (kCMTimeZero)无关。您可以使用第一个缓冲区表示时间戳作为源时间。

附注：大概46小时左右是你的设备正常运行时间。