.
.

public void CaptureScreen(string fileName,ImageFormat imageFormat)
      {
            int hdcSrc = User32.GetWindowDC(User32.GetDesktopWindow()), 
                hdcDest = GDI32.CreateCompatibleDC(hdcSrc),
                hBitmap = GDI32.CreateCompatibleBitmap(hdcSrc,
                GDI32.GetDeviceCaps(hdcSrc,8),GDI32.GetDeviceCaps(hdcSrc,10)); 
            GDI32.SelectObject(hdcDest,hBitmap);
            GDI32.BitBlt(hdcDest,0,0,GDI32.GetDeviceCaps(hdcSrc,8),
                            GDI32.GetDeviceCaps(hdcSrc,10),
                            hdcSrc,0,0,0x00CC0020);
            SaveImageAs(hBitmap,fileName,imageFormat);
            Cleanup(hBitmap,hdcSrc,hdcDest);
      }
.
.
.

.
.
public void AddFrame(Bitmap bmp) {
    BitmapData bmpDat = bmp.LockBits(
        new Rectangle(0, 0, bmp.Width, bmp.Height),
        ImageLockMode.ReadOnly,PixelFormat.Format24bppRgb);

    //this is the first frame - get size and create a new stream
    if (this.countFrames == 0) {
        this.stride = (UInt32)bmpDat.Stride;
        this.width = bmp.Width;
        this.height = bmp.Height;
        CreateStream(); //a method to create a new video stream
    }

    //add the bitmap to the stream
    int result = AVIStreamWrite(aviStream,
        countFrames, 1, 
        bmpDat.Scan0, //pointer to the beginning of the image data
        (Int32) (stride  * height), 
        0, 0, 0); 

    bmp.UnlockBits(bmpDat);
    this.countFrames ++;
}
.
.