swift - AssetReader/AssetWriter - CMSampleBuffer 和 CALayer

Question

我正在对视频进行转码，以将 ML Vision 的绘图嵌入到新视频中。方法是使用avassetreader 和avassetwriter。我将 cmsamplebuffer 传递给视觉并获得结果。我用结果构建了 calayer。我不确定如何将 cmsamplebuffer 与 calayer 与图纸相协调。

这是片段

func transcode(completion: @escaping (AVURLAsset) -> Void) {
    
    var videoComposition = AVVideoComposition()
    var composition = AVComposition(url: model.assetInfo.asset.url)
    let tracks = composition.tracks(withMediaType: .video)
    var videoSettings = [String(kCVPixelBufferPixelFormatTypeKey): NSNumber(value: kCVPixelFormatType_420YpCbCr8PlanarFullRange)]
    
    let videoCompositionOutput = AVAssetReaderVideoCompositionOutput(videoTracks: tracks, videoSettings: videoSettings)
    
    videoCompositionOutput.videoComposition = videoComposition
    
    if reader.canAdd(videoCompositionOutput) {
        reader.add(videoCompositionOutput)
    }
    else {
        fatalError()
    }
    
    self.reader.startReading()
    
    var isDone = false
    
    while(!isDone) {
        if let buffer = videoCompositionOutput.copyNextSampleBuffer(),
           let imageBuffer = CMSampleBufferGetImageBuffer(buffer) {
        
           let ciimage = CIImage(cvImageBuffer: imageBuffer)
           let context = CIContext()
            
           if let cgImage = context.createCGImage(ciimage, from: ciimage.extent) {
                let uiImage = UIImage(cgImage: cgImage)
                
                let frame = CGRect(origin: .zero, size: uiImage.size)
                
                let visionDirector = VisionDirector()
            
                visionDirector.createVisionProductByDrawingTypeAndBuffer(drawingType: .ML, cmSampleBuffer: buffer) {
                    (visionProduct) in
                    
                    let model = CALayerFactoryByDrawTypeModel(frame: frame, drawingType: .ML, visionProduct: visionProduct)
                    let factory = CALayerFactoryByDrawType(model: model)
                    let layer = factory.build()
                    
                    //how do we get the calayer embedded on the cmsamplebuffer?
                    //then we'll stream the cmsamplebuffer in the avassetwriter for a new video.
                }
                
           }
            
        }
        else {
            if self.reader.status == .failed, let error = reader.error?.localizedDescription {
                fatalError(error)
            }
            else {
                isDone = true
            }
        }
        
    }
}