说明：  簡單的 DirectShow 抓取程式 使用ICaptureGraphBuilder2 及 ICreateDevEnum 來創建 capture 圖形
(Simple capture application. This application creates a preview window for the first video capture device that it locates on the user s system (if any). It demonstrates a simple example of using the ICaptureGraphBuilder2 and ICreateDevEnum interfaces to build a capture graph.)