通过 AVAssetWriter 捕获视频并保存

Question

我想将 AVAssetWriter 输出保存到相机胶卷，我目前正在将它保存到文档目录。

我试过使用 UISaveVideoAtPathToSavedPhotosAlbum(_:_:_:_:) 。我目前正在使用 AVAssetWriter 写入 .documentsdirectotry。但是，当我尝试编写时，它会默默地失败。要写，我会调用startRecording()，我会调用stopRecording()来写完。

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)
        }
    }
}

当前的实现设置了相机和预览，但随后没有任何内容保存到输出中。它应该保存到 .documentDirectory，但是，它没有保存。我想改为将其保存到相机胶卷，但我不确定我应该在哪里调用 UISaveVideoAtPathToSavedPhotosAlbum(_:_:_:_:)。问题可能出在我的扩展委托中。

提前感谢您的帮助。

Answer 1

我不熟悉 UISaveVideoAtPathToSavedPhotosAlbum。但是浏览堆栈溢出和 git，许多人使用 PHPhotoLibrary，我也是。不管 url，下面的代码将视频添加到 photoLibrary。

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

1) Info.plist 通过 + 按钮添加新的键值对。 Select "Privary - Photo Library Usage Description" 作为键。设置值类似于 "save video in photo library"

2) 代码

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")
        }
    }
}

希望这对您有所帮助。毛

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