使用vfw将USB摄像头拍摄的画面保存成yuv420格式文件-Vfw to use USB camera to save the screen shot into yuv420 format file

能实现VFW编程，调用本地视频设备，实现视频捕捉和RGB-YUV颜色空间转换。 -To achieve VFW programming, call the local video equipment, the implementation of video capture and RGB-YUV color space conversion.