Swift 4 - avfoundation screen and audio recording using AVAssetWriter on mac os - video frozen

Question

I'm using Aperture to record audio and video from screen. We need to lower the bitrate of video, so i'm trying to rewrite it and record video with AVAssetWriter. My implementation is based on CustomCamera project and is almost working. The problem is in video, after few seconds it is frozen, althought audio is working. Could you help me please? I dont know where the problem is, maybe it is problem with buffers or garbage collector collect some variable. thanks.

Here is the code:

//
//  ViewController.swift
//  CustomCamera
//
//  Created by Taras Chernyshenko on 6/27/17.
//  Copyright © 2017 Taras Chernyshenko. All rights reserved.
//
import AVFoundation
import Photos

class NewRecorder: NSObject,
  AVCaptureAudioDataOutputSampleBufferDelegate,
AVCaptureVideoDataOutputSampleBufferDelegate {

  private var session: AVCaptureSession = AVCaptureSession()
  private var deviceInput: AVCaptureScreenInput?
  private var previewLayer: AVCaptureVideoPreviewLayer?
  private var videoOutput: AVCaptureVideoDataOutput = AVCaptureVideoDataOutput()
  private var audioOutput: AVCaptureAudioDataOutput = AVCaptureAudioDataOutput()

  //private var videoDevice: AVCaptureDevice = AVCaptureScreenInput(displayID: 69731840) //AVCaptureDevice.default(for: AVMediaType.video)!
  private var audioConnection: AVCaptureConnection?
  private var videoConnection: AVCaptureConnection?

  private var assetWriter: AVAssetWriter?
  private var audioInput: AVAssetWriterInput?
  private var videoInput: AVAssetWriterInput?

  private var fileManager: FileManager = FileManager()
  private var recordingURL: URL?

  private var isCameraRecording: Bool = false
  private var isRecordingSessionStarted: Bool = false

  private var recordingQueue = DispatchQueue(label: "recording.queue")


  func setup() {
    self.session.sessionPreset = AVCaptureSession.Preset.high

    self.recordingURL = URL(fileURLWithPath: "\(NSTemporaryDirectory() as String)/file.mp4")
    if self.fileManager.isDeletableFile(atPath: self.recordingURL!.path) {
      _ = try? self.fileManager.removeItem(atPath: self.recordingURL!.path)
    }

    self.assetWriter = try? AVAssetWriter(outputURL: self.recordingURL!,
                                          fileType: AVFileType.mp4)
    self.assetWriter!.movieFragmentInterval = kCMTimeInvalid
    self.assetWriter!.shouldOptimizeForNetworkUse = true

    let audioSettings = [
      AVFormatIDKey : kAudioFormatMPEG4AAC,
      AVNumberOfChannelsKey : 2,
      AVSampleRateKey : 44100.0,
      AVEncoderBitRateKey: 192000
      ] as [String : Any]

    let videoSettings = [
      AVVideoCodecKey : AVVideoCodecType.h264,
      AVVideoWidthKey : 1920,
      AVVideoHeightKey : 1080
      /*AVVideoCompressionPropertiesKey: [
        AVVideoAverageBitRateKey:  NSNumber(value: 5000000)
      ]*/
      ] as [String : Any]

    self.videoInput = AVAssetWriterInput(mediaType: AVMediaType.video,
                                         outputSettings: videoSettings)
    self.audioInput = AVAssetWriterInput(mediaType: AVMediaType.audio,
                                         outputSettings: audioSettings)

    self.videoInput?.expectsMediaDataInRealTime = true
    self.audioInput?.expectsMediaDataInRealTime = true

    if self.assetWriter!.canAdd(self.videoInput!) {
      self.assetWriter?.add(self.videoInput!)
    }

    if self.assetWriter!.canAdd(self.audioInput!) {
      self.assetWriter?.add(self.audioInput!)
    }

    //self.deviceInput = try? AVCaptureDeviceInput(device: self.videoDevice)
    self.deviceInput = AVCaptureScreenInput(displayID: 724042646)
    self.deviceInput!.minFrameDuration = CMTimeMake(1, Int32(30))
    self.deviceInput!.capturesCursor = true
    self.deviceInput!.capturesMouseClicks = true

    if self.session.canAddInput(self.deviceInput!) {
      self.session.addInput(self.deviceInput!)
    }

    self.previewLayer = AVCaptureVideoPreviewLayer(session: self.session)

    //importent line of code what will did a trick
    //self.previewLayer?.videoGravity = AVLayerVideoGravity.resizeAspectFill

    //let rootLayer = self.view.layer
    //rootLayer.masksToBounds = true
    //self.previewLayer?.frame = CGRect(x: 0, y: 0, width: 1920, height: 1080)

    //rootLayer.insertSublayer(self.previewLayer!, at: 0)

    self.session.startRunning()

    DispatchQueue.main.async {
      self.session.beginConfiguration()

      if self.session.canAddOutput(self.videoOutput) {
        self.session.addOutput(self.videoOutput)
      }

      self.videoConnection = self.videoOutput.connection(with: AVMediaType.video)
      /*if self.videoConnection?.isVideoStabilizationSupported == true {
        self.videoConnection?.preferredVideoStabilizationMode = .auto
      }*/
      self.session.commitConfiguration()

      let audioDevice = AVCaptureDevice.default(for: AVMediaType.audio)
      let audioIn = try? AVCaptureDeviceInput(device: audioDevice!)

      if self.session.canAddInput(audioIn!) {
        self.session.addInput(audioIn!)
      }

      if self.session.canAddOutput(self.audioOutput) {
        self.session.addOutput(self.audioOutput)
      }

      self.audioConnection = self.audioOutput.connection(with: AVMediaType.audio)
    }
  }

  func startRecording() {
    if self.assetWriter?.startWriting() != true {
      print("error: \(self.assetWriter?.error.debugDescription ?? "")")
    }

    self.videoOutput.setSampleBufferDelegate(self, queue: self.recordingQueue)
    self.audioOutput.setSampleBufferDelegate(self, queue: self.recordingQueue)
  }

  func stopRecording() {
    self.videoOutput.setSampleBufferDelegate(nil, queue: nil)
    self.audioOutput.setSampleBufferDelegate(nil, queue: nil)

    self.assetWriter?.finishWriting {
      print("Saved in folder \(self.recordingURL!)")
      exit(0)
    }
  }
  func captureOutput(_ captureOutput: AVCaptureOutput, didOutput
    sampleBuffer: CMSampleBuffer, from connection: AVCaptureConnection) {

    if !self.isRecordingSessionStarted {
      let presentationTime = CMSampleBufferGetPresentationTimeStamp(sampleBuffer)
      self.assetWriter?.startSession(atSourceTime: presentationTime)
      self.isRecordingSessionStarted = true
    }

    let description = CMSampleBufferGetFormatDescription(sampleBuffer)!

    if CMFormatDescriptionGetMediaType(description) == kCMMediaType_Audio {
      if self.audioInput!.isReadyForMoreMediaData {
        //print("appendSampleBuffer audio");
        self.audioInput?.append(sampleBuffer)
      }
    } else {
      if self.videoInput!.isReadyForMoreMediaData {
        //print("appendSampleBuffer video");
        if !self.videoInput!.append(sampleBuffer) {
          print("Error writing video buffer");
        }
      }
    }
  }
}

Answer 1

So I fixed it by moving this code

if self.session.canAddInput(self.deviceInput!) {
  self.session.addInput(self.deviceInput!)
}

after the call self.session.beginConfiguration(), so

self.session.beginConfiguration()
  if self.session.canAddInput(self.deviceInput!) {
    self.session.addInput(self.deviceInput!)
  }

  if self.session.canAddOutput(self.videoOutput) {
    self.session.addOutput(self.videoOutput)
  }

  self.videoConnection = self.videoOutput.connection(with: AVMediaType.video)

  self.session.commitConfiguration()