The parameters contained in the usb_cam node are:
- param name="video_device" value="/dev/video0".
- param name="image_width" value="640".
- param name="image_height" value="480".
- param name="pixel_format" value="yuyv".
- param name="camera_frame_id" value="usb_cam".
- param name="io_method" value="mmap".