Swift AVAssetWriter-如果呼叫次数过多，则不会'；行不通

我想压缩一下我的视频。为此，我编写了一个@escaping函数。我从要压缩的数据中传入URL，然后从压缩文件中检索新的URL。问题是：当4项->1项损坏时，3项工作正常，当更多项损坏时：许多项损坏。输入的URL是正确的，并且有数据，那么我在这里做错了什么

   class Compress() {
     ...code below
   }

我的压缩功能

    var bitrate: NSNumber = 50000
        
    func compressFile(urlToCompress: URL, outputURL: URL, completion:@escaping (URL)->Void) {
        
        var assetWriter:AVAssetWriter?
        var assetReader:AVAssetReader?
        
        var audioFinished = false
        var videoFinished = false
        
        let asset = AVAsset(url: urlToCompress);

        do {
            assetReader = try AVAssetReader(asset: asset)
        } catch {
           assetReader = nil
        }
        
        guard let reader = assetReader else {
            fatalError("Could not initalize asset reader probably failed its try catch")
        }
        
        let videoTrack = asset.tracks(withMediaType: AVMediaType.video).first!
        let audioTrack = asset.tracks(withMediaType: AVMediaType.audio).first!
        
        let videoReaderSettings: [String:Any] =  [kCVPixelBufferPixelFormatTypeKey as String:kCVPixelFormatType_32ARGB ]
            // ADJUST BIT RATE OF VIDEO HERE
            let videoSettings:[String:Any] = [
                AVVideoCompressionPropertiesKey: [AVVideoAverageBitRateKey:self.bitrate],
                AVVideoCodecKey: AVVideoCodecType.h264,
                AVVideoHeightKey: videoTrack.naturalSize.height,
                AVVideoWidthKey: videoTrack.naturalSize.width
            ]
        
        let assetReaderVideoOutput = AVAssetReaderTrackOutput(track: videoTrack, outputSettings: videoReaderSettings)
        let assetReaderAudioOutput = AVAssetReaderTrackOutput(track: audioTrack, outputSettings: nil)
        if reader.canAdd(assetReaderVideoOutput){
            reader.add(assetReaderVideoOutput)
        }else{
            fatalError("Couldn't add video output reader")
        }
        if reader.canAdd(assetReaderAudioOutput){
            reader.add(assetReaderAudioOutput)
        }else{
            fatalError("Couldn't add audio output reader")
        }
        
        let audioInput = AVAssetWriterInput(mediaType: AVMediaType.audio, outputSettings: nil)
        let videoInput = AVAssetWriterInput(mediaType: AVMediaType.video, outputSettings: videoSettings)
             videoInput.transform = videoTrack.preferredTransform
        
        let videoInputQueue = DispatchQueue(label: "videoQueue")
        let audioInputQueue = DispatchQueue(label: "audioQueue")
            do {
                assetWriter = try AVAssetWriter(outputURL: outputURL, fileType: AVFileType.mov)
            } catch {
                assetWriter = nil
            }
            guard let writer = assetWriter else {
                fatalError("assetWriter was nil")
            }
        
        writer.shouldOptimizeForNetworkUse = true
        writer.add(videoInput)
        writer.add(audioInput)
        writer.startWriting()
        reader.startReading()
        writer.startSession(atSourceTime: CMTime.zero)
        
        let closeWriter:()->Void = {
            if (audioFinished && videoFinished){
                assetWriter?.finishWriting(completionHandler: {
                    completion((assetWriter?.outputURL)!)
                })
                assetReader?.cancelReading()
            }
        }
        
        audioInput.requestMediaDataWhenReady(on: audioInputQueue) {
            while(audioInput.isReadyForMoreMediaData){
                let sample = assetReaderAudioOutput.copyNextSampleBuffer()
                if (sample != nil){
                    audioInput.append(sample!)
                }else{
                    audioInput.markAsFinished()
                    DispatchQueue.main.async {
                        audioFinished = true
                        closeWriter()
                    }
                    break;
                }
            }
        }
        videoInput.requestMediaDataWhenReady(on: videoInputQueue) {
            //request data here
            while(videoInput.isReadyForMoreMediaData){
                let sample = assetReaderVideoOutput.copyNextSampleBuffer()
                if (sample != nil){
                    videoInput.append(sample!)
                }else{
                    videoInput.markAsFinished()
                    DispatchQueue.main.async {
                        videoFinished = true
                        closeWriter()
                    }
                    break;
                }
            }
        }
    }

我如何调用函数

let group = DispatchGroup()

                for video in videos {
                        group.enter()
                        let formatter = DateFormatter()
                        formatter.dateFormat = "yyyy'-'MM'-'dd'T'HH':'mm':'ss'Z'"
                        let date = Date()
                        let documentsPath = NSTemporaryDirectory()
                        let outputPath = "\(documentsPath)/\(formatter.string(from: date))\(video.id).mp4"
                        let newOutputUrl = URL(fileURLWithPath: outputPath)
                        var videoData = Data()
                        self.compressFile(urlToCompress: video.assetURL, outputURL: newOutputUrl) { (URL) in
                            videoData = try! NSData(contentsOf: newOutputUrl, options: .mappedIfSafe) as Data
                            finishedVideoArray.append(videoData as Data)
                            group.leave()
                        }
                }