这是一个Linux下的USB摄像头捕捉程序，是一个调用v4l2 （Video for Linux 2）非常好的例子。英文介绍为：This is a driver for the USB video bridge USBVision from Zoran/Nogatech, a USB-only cable used in many \"webcam\" devices. It supports streaming and capture of color or monochrome video

unicap provides an uniform access to video capture devices. Currently you can access v4l, v4l2, IIDC 1394 ( DCAM ) cameras and video to firewire converters with a single API. New devices can be added via a plugin system.

V4L视频采集，代码是通过调用V4l的API来实现的。-V4L video capture code to achieve is by call V4l the API.