How to set FPS in opencvsharp videocapture library?

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C#

OpenCV

I just copied an program to detect faces through video but the video capture is really slow, and i dont know how to fix it! Every time when I change the FPS same value is return which is 59.98... I try lots of solution in Stack (mostly use C++ language and thread or timer tick ) but still I get the same fps.

What I have tried:

private void StartButton_Click(object sender, EventArgs e)
       {
           grabber = new VideoCapture(videoPath);
           grabber.QueryFrame();
           //System.Threading.Thread.Sleep(1000);
           grabber.SetCaptureProperty(CapProp.Fps, 100); //fps setting  default 5
           Console.WriteLine("Show FPS   ->>>> " + grabber.GetCaptureProperty(CapProp.Fps));
           Application.Idle += new EventHandler(FrameGrabber);
           StartButton.Enabled = false;
       }

       void FrameGrabber(object sender, EventArgs e)
       {
           currentFrame = grabber.QuerySmallFrame(); //Orginalley use QueryFrame() method.
           Image<Bgr, Byte> currentImageFrame = currentFrame.ToImage<Bgr, Byte>();
           currentImageFrame.Resize(320, 240, Emgu.CV.CvEnum.Inter.Cubic);
           gray = currentImageFrame.Convert<Gray, byte>();

           Rectangle[] facesDetected = Face.DetectMultiScale(gray, 1.01, 7, new Size(30, 30));
           numberLabel.Text = "";
           .
           .
           .
        }