Here is some sample code that I use to set the "Zoom, Absolute" control in v4l2. You could replace V4L2_CID_ZOOM_ABSOLUTE with V4L2_CID_AUTO_WHITE_BALANCE to enable/disable auto white-balance.

    struct v4l2_queryctrl queryctrl;
    struct v4l2_control control;

    memset (&queryctrl, 0, sizeof (queryctrl));
    queryctrl.id = V4L2_CID_ZOOM_ABSOLUTE;

    if (-1 == ioctl (capture_fd_, VIDIOC_QUERYCTRL, &queryctrl)) {
      if (errno != EINVAL) {
        perror ("VIDIOC_QUERYCTRL");
        exit (EXIT_FAILURE);
      } else {
        printf ("V4L2_CID_ZOOM_ABSOLUTE is not supported\n");
      }
    } else if (queryctrl.flags & V4L2_CTRL_FLAG_DISABLED) {
      printf ("V4L2_CID_ZOOM_ABSOLUTE is not supported\n");
    } else {
      memset (&control, 0, sizeof (control));
      control.id = V4L2_CID_ZOOM_ABSOLUTE;
      control.value = zoom_factor_;

      if (-1 == ioctl (capture_fd_, VIDIOC_S_CTRL, &control)) {
        perror ("VIDIOC_S_CTRL");
        exit (EXIT_FAILURE);
      }
    }

On Mon, Aug 23, 2010 at 10:01 AM, Ken Tossell <ktossell@umd.edu> wrote:

You also might want to check out libwebcam and its command-line
configuration utility, uvcdynctrl:

http://www.quickcamteam.net/software/libwebcam

$ uvcdynctrl -d /dev/video0 -g 'White Balance Temperature, Auto'
1
$ uvcdynctrl -d /dev/video0 -s 'White Balance Temperature, Auto' 0
$ uvcdynctrl -d /dev/video0 -c
Listing available controls for device /dev/video0:
[...]
Focus (absolute)
Exposure, Auto Priority
Exposure (Absolute)
Exposure, Auto
Backlight Compensation
Sharpness
White Balance Temperature
Power Line Frequency
Gain
White Balance Temperature, Auto
Saturation
Contrast
Brightness

- Ken

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