如何将采集到的视频与avcapturesession合并？

import AVFoundation

// 创建AVCaptureSession
let captureSession = AVCaptureSession()

// 设置输入设备（摄像头）
guard let captureDevice = AVCaptureDevice.default(for: .video),
      let input = try? AVCaptureDeviceInput(device: captureDevice) else {
    fatalError("Failed to create AVCaptureDeviceInput")
}
captureSession.addInput(input)

// 设置输出设备（视频文件输出）
let output = AVCaptureMovieFileOutput()
captureSession.addOutput(output)

// 开始采集视频
captureSession.startRunning()

// 创建AVMutableComposition对象
let composition = AVMutableComposition()

// 创建AVMutableCompositionTrack对象
guard let compositionTrack = composition.addMutableTrack(withMediaType: .video, preferredTrackID: kCMPersistentTrackID_Invalid) else {
    fatalError("Failed to create composition track")
}

// 将采集到的视频样本添加到AVMutableCompositionTrack中
guard let sampleBuffer = output.copyNextSampleBuffer(),
      let formatDescription = CMSampleBufferGetFormatDescription(sampleBuffer) else {
    fatalError("Failed to get sample buffer")
}
try? compositionTrack.insertTimeRange(CMTimeRange(start: .zero, duration: .invalid), of: sampleBuffer, at: .zero)

// 停止采集视频
captureSession.stopRunning()

// 创建AVAssetExportSession对象
guard let exportSession = AVAssetExportSession(asset: composition, presetName: AVAssetExportPresetHighestQuality) else {
    fatalError("Failed to create export session")
}

// 设置输出文件路径和格式
let outputURL = URL(fileURLWithPath: NSTemporaryDirectory()).appendingPathComponent("mergedVideo.mp4")
exportSession.outputURL = outputURL
exportSession.outputFileType = .mp4

// 导出合并后的视频文件
exportSession.exportAsynchronously {
    switch exportSession.status {
    case .completed:
        print("Merge completed. Output file: \(outputURL)")
    case .failed:
        print("Merge failed. Error: \(exportSession.error?.localizedDescription ?? "")")
    case .cancelled:
        print("Merge cancelled.")
    default:
        break
    }
}