如何在Swift中的视频上叠加动态标签？

import AVFoundation

func addDynamicLabelToVideo(videoURL: URL, label: String, position: CGPoint) {
    let composition = AVMutableComposition()
    
    guard let asset = AVAsset(url: videoURL) as? AVURLAsset else {
        return
    }
    
    let videoTrack = composition.addMutableTrack(withMediaType: .video, preferredTrackID: kCMPersistentTrackID_Invalid)
    let audioTrack = composition.addMutableTrack(withMediaType: .audio, preferredTrackID: kCMPersistentTrackID_Invalid)
    
    guard let assetVideoTrack = asset.tracks(withMediaType: .video).first else {
        return
    }
    
    guard let assetAudioTrack = asset.tracks(withMediaType: .audio).first else {
        return
    }
    
    do {
        try videoTrack?.insertTimeRange(CMTimeRange(start: .zero, duration: asset.duration), of: assetVideoTrack, at: .zero)
        try audioTrack?.insertTimeRange(CMTimeRange(start: .zero, duration: asset.duration), of: assetAudioTrack, at: .zero)
    } catch {
        return
    }
    
    let videoSize = assetVideoTrack.naturalSize
    
    let videoComposition = AVMutableVideoComposition()
    videoComposition.renderSize = videoSize
    videoComposition.frameDuration = CMTime(value: 1, timescale: 30)
    
    let instruction = AVMutableVideoCompositionInstruction()
    instruction.timeRange = CMTimeRange(start: .zero, duration: composition.duration)
    
    let layerInstruction = AVMutableVideoCompositionLayerInstruction(assetTrack: videoTrack!)
    layerInstruction.setTransform(assetVideoTrack.preferredTransform, at: .zero)
    
    let textLayer = CATextLayer()
    textLayer.string = label
    textLayer.font = UIFont.systemFont(ofSize: 24)
    textLayer.fontSize = 24
    textLayer.foregroundColor = UIColor.white.cgColor
    textLayer.alignmentMode = .center
    textLayer.frame = CGRect(x: position.x, y: position.y, width: videoSize.width, height: videoSize.height)
    
    let overlayLayer = CALayer()
    overlayLayer.addSublayer(textLayer)
    overlayLayer.frame = CGRect(x: 0, y: 0, width: videoSize.width, height: videoSize.height)
    
    let parentLayer = CALayer()
    parentLayer.frame = CGRect(x: 0, y: 0, width: videoSize.width, height: videoSize.height)
    parentLayer.addSublayer(overlayLayer)
    
    videoComposition.animationTool = AVVideoCompositionCoreAnimationTool(postProcessingAsVideoLayer: videoTrack!, in: parentLayer)
    
    instruction.layerInstructions = [layerInstruction]
    videoComposition.instructions = [instruction]
    
    let exportSession = AVAssetExportSession(asset: composition, presetName: AVAssetExportPresetHighestQuality)
    
    guard let exportSession = exportSession else {
        return
    }
    
    let outputURL = // 设置导出视频的输出路径
    
    exportSession.outputURL = outputURL
    exportSession.outputFileType = .mp4
    exportSession.videoComposition = videoComposition
    
    exportSession.exportAsynchronously {
        // 导出完成后的处理
    }
}