capture desktop screen as video in wpf/Windows

Maybe it would be easier to capture the desktop at interval rates, and then encode each image into a video file using a plugin or an external library.

Check those:
http://bytescout.com/products/developer/imagetovideosdk/imagetovideosdk_first_step_with_visual_c_sharp_net.html[^]

A Simple C# Wrapper for the AviFile Library[^]

About how to capture your destop, it's easy. You create a bitmap with the size of the screen, then a Graphics from the bitmap, and then copy the screen and save it:

private void TakeScreenShot()
{
    Bitmap bmpScreenshot = new Bitmap(Screen.PrimaryScreen.Bounds.Width, Screen.PrimaryScreen.Bounds.Height, PixelFormat.Format32bppArgb);

    Graphics gfxScreenshot = Graphics.FromImage(bmpScreenshot);

    gfxScreenshot.CopyFromScreen(0, 0, 0, 0, Screen.PrimaryScreen.Bounds.Size, CopyPixelOperation.SourceCopy);

    //Change the ImageFormat to jpeg to save hard disk or keep it in Tiff
    //for higher resolution
    bmpScreenshot.Save("Dependencies\\temp.tif", ImageFormat.Tiff);
    bmpScreenshot = null;
}

You can adictionally use an external program like VirtualDub. Maybe you can make a script for it, and run it from your program. I know this is not the way you're intended to do it, but it's another way.