There is much more to DirectShow than I could cover in this brief article. For example, DirectShow supports different kinds of video renderers, which support windowless mode—the renderer draws directly onto an application window's client area rather than in a separate window. I suspect that windowless mode results in less video jerkiness when the application's window is moved around the screen.
If you want to learn more about DirectShow, I recommend checking out the many interesting articles hosted at The Code Project and codeguru. And don't forget to check out Microsoft's official DirectShow documentation on which this article is based.