Capturing video and saving it via AVAssetWriter

I want to save AVAssetWriter output to the camera roll, I'm currently saving it to the documents directory.

I have tried to use the UISaveVideoAtPathToSavedPhotosAlbum(_:_:_:_:) . I am currently using AVAssetWriter to write to the .documentsdirectotry. However, when I try to write, it fails silently. To write, I'll call startRecording() and I'll call stopRecording() to finish writing.

let captureSession = AVCaptureSession()
var videoOutput = AVCaptureVideoDataOutput()
var assetWriter: AVAssetWriter!
var assetWriterInput: AVAssetWriterInput!
var isCameraSetup = false
var hasStartedWritingCurrentVideo  = false
var isWriting = false
let queue = DispatchQueue(label: "com.name.camera-queue") 


// Camera preview setup code

//Setting up Asset Writer to save videos
public func setUpAssetWriter() {
    do {
        let documentsPath = NSSearchPathForDirectoriesInDomains(.documentDirectory, .userDomainMask, true).first
        let outputURL = URL(fileURLWithPath: documentsPath!).appendingPathComponent("test.m4v")
        assetWriter = try! AVAssetWriter(outputURL: outputURL, fileType: .mp4)
        assetWriterInput = AVAssetWriterInput(mediaType: .video, outputSettings: videoOutput.recommendedVideoSettingsForAssetWriter(writingTo: .mp4))
        assetWriterInput.expectsMediaDataInRealTime = true

        if assetWriter.canAdd(assetWriterInput) {
            assetWriter.add(assetWriterInput)
        } else {
            print("no input added")
        }
        assetWriter.startWriting()
        } catch let error {
        debugPrint(error.localizedDescription)
    }
}
public func tearDownAssetWriter() {
    assetWriter = nil
    assetWriterInput = nil
}
public func startWriting(){
    if isWriting{ return }
        setUpAssetWriter()
        hasStartedWritingCurrentVideo = false
        isWriting = true
}
public func finishWriting(_ completion: @escaping (URL) -> Void) {
    if isWriting == false { return }
    isWriting = false
    assetWriterInput.markAsFinished()
    let url = self.assetWriter.outputURL
    assetWriter.finishWriting {
        completion(url)
        self.tearDownAssetWriter()
    }
    hasStartedWritingCurrentVideo = false
}

// MARK: Starts the capture session
public func start() {
    if !captureSession.isRunning {
        captureSession.startRunning()
    }
}

public func stop() {
    if captureSession.isRunning {
        captureSession.stopRunning()
    }
}
// MARK: Records after camera is set up
public func startRecording() {
    startWriting()
    isWriting = true
}

public func stopRecording() {
    assetWriterInput.markAsFinished()
    assetWriter.finishWriting {
        [weak self] in return
    }
}
}

extension VideoCapture: AVCaptureVideoDataOutputSampleBufferDelegate {
    public func captureOutput(_ output: AVCaptureOutput, didOutput sampleBuffer: CMSampleBuffer, from connection: AVCaptureConnection) {
        // Because lowering the capture device's FPS looks ugly in the preview,
        // we capture at full speed but only call the delegate at its desired
        // framerate.
        let timestamp = CMSampleBufferGetPresentationTimeStamp(sampleBuffer)
        let deltaTime = timestamp - lastTimestamp
        if deltaTime >= CMTimeMake(value: 1, timescale: Int32(fps)) {
            lastTimestamp = timestamp
            let imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer)
            delegate?.videoCapture(self, didCaptureVideoFrame: imageBuffer, timestamp: timestamp)
        }
    // Asset Writer
        guard let assetWriter = assetWriter, let assetWriterInput = assetWriterInput else { return }
        if isWriting == false{ return }
        if self.assetWriter.status == .failed {
            setUpAssetWriter()
            hasStartedWritingCurrentVideo = false
        }
        if hasStartedWritingCurrentVideo == false && output === videoOutput { return }
        if hasStartedWritingCurrentVideo == false {
            hasStartedWritingCurrentVideo = true
            let sourceTime = CMSampleBufferGetPresentationTimeStamp(sampleBuffer)
            assetWriter.startSession(atSourceTime: sourceTime)
        }
        if output === videoOutput && assetWriterInput.isReadyForMoreMediaData{
            if isWriting == false{return}
            assetWriterInput.append(sampleBuffer)
        }
    }
}

The current implementation sets up the camera and preview, but then nothing is saved to the output. It should save to the .documentDirectory, however, it's not saving. I would like to instead get it to save to the camera roll, but I'm not sure where exactly I should call UISaveVideoAtPathToSavedPhotosAlbum(_:_:_:_:). The problem is likely in my extension delegate.

Thank you in advance for your help.

I am not familiar with UISaveVideoAtPathToSavedPhotosAlbum. But browsing stack overflow and git, many people use PHPhotoLibrary and so do I. Regardless of url, code below adds the video to photoLibrary.

https://developer.apple.com/documentation/photokit/phassetchangerequest/1624057-creationrequestforassetfromvideo

1) Info.plist Add new key-value pair by + button. Select "Privary - Photo Library Usage Description" as a key. Set value something like "save video in photo library"

2) code

fileWriter.finishWriting(completionHandler: {
    let status = PHPhotoLibrary.authorizationStatus()

    //no access granted yet
    if status == .notDetermined || status == .denied{
        PHPhotoLibrary.requestAuthorization({auth in
            if auth == .authorized{
                saveInPhotoLibrary(url)
            }else{
                print("user denied access to photo Library")
            }
        })

    //access granted by user already
    }else{
        saveInPhotoLibrary(url)
    }
})

private func saveInPhotoLibrary(_ url:URL){
    PHPhotoLibrary.shared().performChanges({

        //add video to PhotoLibrary here
        PHAssetChangeRequest.creationRequestForAssetFromVideo(atFileURL: url)
    }) { completed, error in
        if completed {
            print("save complete! path : " + url.absoluteString)
        }else{
            print("save failed")
        }
    }
}

Hope this helps. GW