1. fps > 15 is not stable in uvc, so set the frame rate = 10fps
2. video capture is YUYV422
3. video format, VIDIOC_S_FMT , can only be set once after buffer is allocated.
the buffer should be released to set the video format again.
4. cvShowImage needs a little bit delay by cvWaitKey(1);
5. yuyv_to_rgb24 is from opencv/modules/highgui/src/cap_v4l.cpp.