如何在iOS中为视频添加多个文字，如图所示？

import AVFoundation

func addTextToVideo(videoURL: URL, textLayers: [CATextLayer], completion: @escaping (URL?, Error?) -> Void) {
    let videoAsset = AVURLAsset(url: videoURL)
    
    let composition = AVMutableComposition()
    guard let videoTrack = composition.addMutableTrack(withMediaType: .video, preferredTrackID: kCMPersistentTrackID_Invalid),
          let audioTrack = composition.addMutableTrack(withMediaType: .audio, preferredTrackID: kCMPersistentTrackID_Invalid) else {
        completion(nil, NSError(domain: "com.example", code: 0, userInfo: [NSLocalizedDescriptionKey: "Failed to create video/audio track"]))
        return
    }
    
    guard let assetVideoTrack = videoAsset.tracks(withMediaType: .video).first,
          let assetAudioTrack = videoAsset.tracks(withMediaType: .audio).first else {
        completion(nil, NSError(domain: "com.example", code: 0, userInfo: [NSLocalizedDescriptionKey: "Failed to load video/audio track from asset"]))
        return
    }
    
    do {
        try videoTrack.insertTimeRange(CMTimeRange(start: .zero, duration: videoAsset.duration), of: assetVideoTrack, at: .zero)
        try audioTrack.insertTimeRange(CMTimeRange(start: .zero, duration: videoAsset.duration), of: assetAudioTrack, at: .zero)
    } catch {
        completion(nil, error)
        return
    }
    
    let videoSize = assetVideoTrack.naturalSize
    
    let videoComposition = AVMutableVideoComposition()
    videoComposition.renderSize = videoSize
    videoComposition.frameDuration = CMTime(value: 1, timescale: 30) // 设置帧率
    
    let instruction = AVMutableVideoCompositionInstruction()
    instruction.timeRange = CMTimeRange(start: .zero, duration: videoAsset.duration)
    
    let layerInstruction = AVMutableVideoCompositionLayerInstruction(assetTrack: videoTrack)
    instruction.layerInstructions = [layerInstruction]
    
    videoComposition.instructions = [instruction]
    
    for textLayer in textLayers {
        let textInstruction = AVMutableVideoCompositionInstruction()
        textInstruction.timeRange = CMTimeRange(start: .zero, duration: videoAsset.duration)
        
        let textLayerInstruction = AVMutableVideoCompositionLayerInstruction(assetTrack: videoTrack)
        textLayerInstruction.setTransform(assetVideoTrack.preferredTransform, at: .zero)
        textLayerInstruction.setOpacity(0.0, at: videoAsset.duration)
        
        textInstruction.layerInstructions = [textLayerInstruction]
        videoComposition.instructions.append(textInstruction)
        
        let textAnimation = CABasicAnimation(keyPath: "opacity")
        textAnimation.fromValue = 0.0
        textAnimation.toValue = 1.0
        textAnimation.beginTime = AVCoreAnimationBeginTimeAtZero
        textAnimation.duration = CMTimeGetSeconds(videoAsset.duration)
        textAnimation.isRemovedOnCompletion = false
        textAnimation.fillMode = .forwards
        
        textLayer.add(textAnimation, forKey: "textOpacity")
        videoComposition.animationTool = AVVideoCompositionCoreAnimationTool(postProcessingAsVideoLayer: videoLayer, in: videoComposition)
    }
    
    let outputURL = URL(fileURLWithPath: NSTemporaryDirectory()).appendingPathComponent("output.mp4")
    
    guard let exportSession = AVAssetExportSession(asset: composition, presetName: AVAssetExportPresetHighestQuality) else {
        completion(nil, NSError(domain: "com.example", code: 0, userInfo: [NSLocalizedDescriptionKey: "Failed to create export session"]))
        return
    }
    
    exportSession.outputURL = outputURL
    exportSession.outputFileType = .mp4
    exportSession.shouldOptimizeForNetworkUse = true
    exportSession.videoComposition = videoComposition
    
    exportSession.exportAsynchronously {
        switch exportSession.status {
        case .completed:
            completion(outputURL, nil)
        case .failed, .cancelled:
            completion(nil, exportSession.error)
        default:
            break
        }
    }
}