为什么AVAssetWriter创建的文件大小为0？

Question

I'm trying recording video which filtered by custom CIFilters. And succeeded to create file and previewing. But exported file size is ZERO and couldn't open. But no error occured in debbuger and no crash. Why happens this ??

My code is here.

import UIKit
import AVFoundation
import RxCocoa
import RxSwift

class CameraViewController: UIViewController, AVCaptureVideoDataOutputSampleBufferDelegate {

    private let disposeBag = DisposeBag()

    let camPreview = UIView()
    let imageView = UIImageView()
    var camera: AVCaptureDevice!
    var videoInput: AVCaptureDeviceInput!
    let captureSession = AVCaptureSession()

    private lazy var videoOutput: AVCaptureVideoDataOutput! = {
        let videoOutput = AVCaptureVideoDataOutput()
        videoOutput.setSampleBufferDelegate(self, queue: DispatchQueue.main)
        videoOutput.alwaysDiscardsLateVideoFrames = true
        return videoOutput
    }()

    var assetWriter: AVAssetWriter!
    var videoAssetInput: AVAssetWriterInput!
    var pixelBuffer: AVAssetWriterInputPixelBufferAdaptor!
    var startTime: CMTime!
    var endTime: CMTime!
    var frameNumber: Int64 = 0

    override func viewDidLoad() {
        super.viewDidLoad()

        self.view.backgroundColor = UIColor.white

        imageView.backgroundColor = UIColor.groupTableViewBackground
        imageView.contentMode = .scaleAspectFill
        imageView.layer.masksToBounds = true
        self.view.addSubview(imageView)
        imageView.snp.makeConstraints { make in
            make.edges.equalToSuperview()
        }
        self.view.layoutIfNeeded()

        if setupSession() {
            startSession()
        }

        let startButton = UIButton()
        startButton.setTitle("startButton", for: .normal)
        startButton.rx.controlEvent(.touchUpInside)
            .asDriver()
            .drive(onNext: { self.startRecording() })
            .disposed(by: disposeBag)
        self.view.addSubview(startButton)
        startButton.snp.makeConstraints { make in
            make.center.equalTo(self.view.snp.center)
        }

        let stopButton = UIButton()
        stopButton.setTitle("stopButton", for: .normal)
        stopButton.rx.controlEvent(.touchUpInside)
            .asDriver()
            .drive(onNext: { self.stopRecording() })
            .disposed(by: disposeBag)
        self.view.addSubview(stopButton)
        stopButton.snp.makeConstraints { make in
            make.centerX.equalTo(self.view.snp.centerX)
            make.top.equalTo(startButton.snp.bottom).offset(30.0)
        }
    }

    private func startRecording() {

        let documentPath = NSHomeDirectory() + "/Documents/"
        let filePath = documentPath + "video.mp4"
        let fileURL = URL(fileURLWithPath: filePath)

        let videoSettings = [
            AVVideoWidthKey: 480,
            AVVideoHeightKey: 640,
            AVVideoCodecKey: AVVideoCodecType.h264
        ] as [String: Any]

        videoAssetInput = AVAssetWriterInput(mediaType: .video, outputSettings: videoSettings)

        pixelBuffer = AVAssetWriterInputPixelBufferAdaptor(assetWriterInput: videoAssetInput, sourcePixelBufferAttributes: [kCVPixelBufferPixelFormatTypeKey as String: Int(kCVPixelFormatType_32BGRA)])
        frameNumber = 0

        do {
            try assetWriter = AVAssetWriter(outputURL: fileURL, fileType: .mp4)
            videoAssetInput.expectsMediaDataInRealTime = true

            assetWriter.add(videoAssetInput)
            assetWriter.startWriting()
            assetWriter.startSession(atSourceTime: CMTime.zero)

            print(#function)
        } catch {
            print(error)
        }
    }

    private func stopRecording() {

        if videoAssetInput == nil { return }

        videoAssetInput.markAsFinished()

        assetWriter.endSession(atSourceTime: endTime)
        assetWriter.finishWriting {
            self.videoAssetInput = nil
        }
    }

    func setupSession() -> Bool {

        captureSession.sessionPreset = AVCaptureSession.Preset.vga640x480

        let camera = AVCaptureDevice.default(for: .video)

        do {
            let input = try AVCaptureDeviceInput(device: camera!)
            if captureSession.canAddInput(input) {
                captureSession.addInput(input)
            }
        } catch {
            print(error)
            return false
        }

        if captureSession.canAddOutput(videoOutput) {
            captureSession.addOutput(videoOutput)
        }

        return true
    }

    func startSession() {
        if !captureSession.isRunning {
            DispatchQueue.main.async {
                self.captureSession.startRunning()
                print(#function)
            }
        }
    }

    func stopSession() {
        if captureSession.isRunning {
            DispatchQueue.main.async {
                self.captureSession.stopRunning()
            }
        }
    }

    func captureOutput(_ output: AVCaptureOutput, didOutput sampleBuffer: CMSampleBuffer, from connection: AVCaptureConnection) {

        autoreleasepool {
            connection.videoOrientation = AVCaptureVideoOrientation.portrait

            guard let pixelBuffer = CMSampleBufferGetImageBuffer(sampleBuffer) else {
                return
            }
            let cameraImage = CIImage(cvPixelBuffer: pixelBuffer)

            let context = CIContext(options: nil)
            let imageRef = context.createCGImage(cameraImage, from: cameraImage.extent)
            let image = UIImage(cgImage: imageRef!)

            DispatchQueue.main.async {
                self.imageView.filter(_image: image)

                guard
                    let videoAssetInput = self.videoAssetInput,
                    let displayedImage = self.imageView.image
                else {
                    return
                }

                if !CMSampleBufferDataIsReady(sampleBuffer) {
                    return
                }
                if self.frameNumber == 0 {
                    self.startTime = CMSampleBufferGetPresentationTimeStamp(sampleBuffer)
                }
                let timestamp = CMSampleBufferGetPresentationTimeStamp(sampleBuffer)
                let frameTime = CMTimeSubtract(timestamp, self.startTime)

                if videoAssetInput.isReadyForMoreMediaData {
                    if let pxBuffer: CVPixelBuffer = self.buffer(from: displayedImage) {
                        self.pixelBuffer.append(pxBuffer, withPresentationTime: frameTime)
                    }
                    self.frameNumber += 1
                }
                self.endTime = frameTime
            }
        }
    }

    func buffer(from image: UIImage) -> CVPixelBuffer? {

        let attrs = [kCVPixelBufferCGImageCompatibilityKey: kCFBooleanTrue, kCVPixelBufferCGBitmapContextCompatibilityKey: kCFBooleanTrue] as CFDictionary
        var pixelBuffer : CVPixelBuffer?
        let status = CVPixelBufferCreate(kCFAllocatorDefault, Int(image.size.width), Int(image.size.height), kCVPixelFormatType_32ARGB, attrs, &pixelBuffer)
        guard (status == kCVReturnSuccess) else {
            return nil
        }

        CVPixelBufferLockBaseAddress(pixelBuffer!, CVPixelBufferLockFlags(rawValue: 0))
        let pixelData = CVPixelBufferGetBaseAddress(pixelBuffer!)

        let rgbColorSpace = CGColorSpaceCreateDeviceRGB()
        let context = CGContext(data: pixelData, width: Int(image.size.width), height: Int(image.size.height), bitsPerComponent: 8, bytesPerRow: CVPixelBufferGetBytesPerRow(pixelBuffer!), space: rgbColorSpace, bitmapInfo: CGImageAlphaInfo.noneSkipFirst.rawValue)

        context?.translateBy(x: 0, y: image.size.height)
        context?.scaleBy(x: 1.0, y: -1.0)

        UIGraphicsPushContext(context!)
        image.draw(in: CGRect(x: 0, y: 0, width: image.size.width, height: image.size.height))
        UIGraphicsPopContext()
        CVPixelBufferUnlockBaseAddress(pixelBuffer!, CVPixelBufferLockFlags(rawValue: 0))

        return pixelBuffer
    }

}

Sorry my codes is still mess, and possibility crash. But it's not the point currently...

Answer 1

The problem is solved. It seems that the video already in the Document directory is getting in the way. When I deleted it, I was able to export the video safely.