i use OpenCvSharp to record video,10 minute per file,but the code i wrote must be somewhere wrong, when i see the video,the video takes 12 minutes 29 seconds.here is the code.

using OpenCvSharp;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace YCamera
{
    public class CameraRecoding
    {

        


        public static void run()
        {
            VideoCapture video = new VideoCapture(0);
            string last_dstr = "";
            VideoWriter videoWriter = null;
            
            while (true)
            {
                string dstr = DateTime.Now.ToString("yyyyMMddHHmm");
                string new_dir = Global_Vals.save_dir;
           
                //record a file per 10 minutes
                if (last_dstr==""||dstr.Substring(0,11) != last_dstr.Substring(0,11))
                {
                    if(videoWriter != null)
                    {

                        videoWriter.Dispose();
                        videoWriter = null;
                    }
                    string new_file = System.IO.Path.Combine(new_dir, "video" + dstr + ".avi");
                    videoWriter = new VideoWriter(new_file,
                    VideoWriter.FourCC(@"XVID"), 20, new Size(640, 480), true);
                    if (!video.IsOpened())
                    {
                        Console.WriteLine("camera open failed");
                        return;
                    }
                 
                   
                }
                
                Mat Camera = new Mat();
                video.Read(Camera);
                if (Camera.Empty())//
                {
                    break;
                }
                videoWriter.Write(Camera);

                last_dstr = dstr;




            }
            


        }
    }
}

i consider if
video.Read(Camera);
take a very long time, and i cannot find a way to change the code,i cannot find similar questions,can any one know how to do so?