url 压缩与 output url url 在 AVAssetReader 和 AVAssetWriter2CD082480506BDD73

Question

我正在努力将实时流媒体视频保存到我的 iPhone 的照片库（现场 stream 也使用我的 iPhone 保存。），我看到这篇文章使用 AVAssetWriter 进行压缩。 下面的代码与他的帖子几乎相同，但我不确定在 function compressFile 的参数中放入什么。 对于两个URL arguments，urlToCompress和outputURL，我应该在里面放什么？

From other post, I created the following URL, and this can be used in either compress URL or output URL?

FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first!.appendingPathComponent("\(filename).mov")



func compressFile(urlToCompress: URL, outputURL: URL, completion:@escaping (URL)->Void){
    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: AVMediaTypeVideo).first!
    let audioTrack = asset.tracks(withMediaType: AVMediaTypeAudio).first!

    let videoReaderSettings: [String:Any] =  [kCVPixelBufferPixelFormatTypeKey as String!:kCVPixelFormatType_32ARGB ]
    
    let videoSettings:[String:Any] = [
        AVVideoCompressionPropertiesKey: [AVVideoAverageBitRateKey:self.bitrate],
        AVVideoCodecKey: AVVideoCodecH264,
        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: AVMediaTypeAudio, outputSettings: nil)
    let videoInput = AVAssetWriterInput(mediaType: AVMediaTypeVideo, outputSettings: videoSettings)
    videoInput.transform = videoTrack.preferredTransform
    
    let videoInputQueue = DispatchQueue(label: "videoQueue")
    let audioInputQueue = DispatchQueue(label: "audioQueue")
    
    do{
        assetWriter = try AVAssetWriter(outputURL: outputURL, fileType: AVFileTypeQuickTimeMovie)
    }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: kCMTimeZero)
    
    
    let closeWriter:()->Void = {
        if (audioFinished && videoFinished){
            self.assetWriter?.finishWriting(completionHandler: {
                
                self.checkFileSize(sizeUrl: (self.assetWriter?.outputURL)!, message: "The file size of the compressed file is: ")
                
                completion((self.assetWriter?.outputURL)!)
                
            })
            
            self.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) {
        
        while(videoInput.isReadyForMoreMediaData){
            let sample = assetReaderVideoOutput.copyNextSampleBuffer()
            if (sample != nil){
                videoInput.append(sample!)
            }else{
                videoInput.markAsFinished()
                DispatchQueue.main.async {
                    videoFinished = true
                    closeWriter()
                }
                break;
            }
        }

    }
    
    
}