设置分辨率和格式
   memset(&fmt,0,sizeof(struct v4l2_format));
   if (driver_type == V4L2_CAP_VIDEO_CAPTURE_MPLANE) {
       fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE;
       fmt.fmt.pix_mp.width = video_width;
       fmt.fmt.pix_mp.height = video_height;
       fmt.fmt.pix_mp.pixelformat = V4L2_PIX_FMT_JPEG;
       fmt.fmt.pix_mp.field = V4L2_FIELD_NONE;
   } else {
       fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
       fmt.fmt.pix.width = video_width;
       fmt.fmt.pix.height = video_height;
       fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_JPEG;
       fmt.fmt.pix.field = V4L2_FIELD_NONE;
   }
   if (ioctl(camera_fd,VIDIOC_S_FMT,&fmt) < 0) {
       perror("VIDIOC_S_FMT failed");
       return -1;
   }