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  <section id="control">
    <title>User Controls</title>

    <para>Devices typically have a number of user-settable controls
such as brightness, saturation and so on, which would be presented to
the user on a graphical user interface. But, different devices
will have different controls available, and furthermore, the range of
possible values, and the default value will vary from device to
device. The control ioctls provide the information and a mechanism to
create a nice user interface for these controls that will work
correctly with any device.</para>

    <para>All controls are accessed using an ID value. V4L2 defines
several IDs for specific purposes. Drivers can also implement their
own custom controls using <constant>V4L2_CID_PRIVATE_BASE</constant>
and higher values. The pre-defined control IDs have the prefix
<constant>V4L2_CID_</constant>, and are listed in <xref
linkend="control-id" />. The ID is used when querying the attributes of
a control, and when getting or setting the current value.</para>

    <para>Generally applications should present controls to the user
without assumptions about their purpose. Each control comes with a
name string the user is supposed to understand. When the purpose is
non-intuitive the driver writer should provide a user manual, a user
interface plug-in or a driver specific panel application. Predefined
IDs were introduced to change a few controls programmatically, for
example to mute a device during a channel switch.</para>

    <para>Drivers may enumerate different controls after switching
the current video input or output, tuner or modulator, or audio input
or output. Different in the sense of other bounds, another default and
current value, step size or other menu items. A control with a certain
<emphasis>custom</emphasis> ID can also change name and
type.<footnote>
	<para>It will be more convenient for applications if drivers
make use of the <constant>V4L2_CTRL_FLAG_DISABLED</constant> flag, but
that was never required.</para>
      </footnote> Control values are stored globally, they do not
change when switching except to stay within the reported bounds. They
also do not change &eg; when the device is opened or closed, when the
tuner radio frequency is changed or generally never without
application request. Since V4L2 specifies no event mechanism, panel
applications intended to cooperate with other panel applications (be
they built into a larger application, as a TV viewer) may need to
regularly poll control values to update their user
interface.<footnote>
	<para>Applications could call an ioctl to request events.
After another process called &VIDIOC-S-CTRL; or another ioctl changing
shared properties the &func-select; function would indicate
readability until any ioctl (querying the properties) is
called.</para>
      </footnote></para>

    <table pgwide="1" frame="none" id="control-id">
      <title>Control IDs</title>
      <tgroup cols="3">
	&cs-def;
	<thead>
	  <row>
	    <entry>ID</entry>
	    <entry>Type</entry>
	    <entry>Description</entry>
	  </row>
	</thead>
	<tbody valign="top">
	  <row>
	    <entry><constant>V4L2_CID_BASE</constant></entry>
	    <entry></entry>
	    <entry>First predefined ID, equal to
<constant>V4L2_CID_BRIGHTNESS</constant>.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CID_USER_BASE</constant></entry>
	    <entry></entry>
	    <entry>Synonym of <constant>V4L2_CID_BASE</constant>.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CID_BRIGHTNESS</constant></entry>
	    <entry>integer</entry>
	    <entry>Picture brightness, or more precisely, the black
level.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CID_CONTRAST</constant></entry>
	    <entry>integer</entry>
	    <entry>Picture contrast or luma gain.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CID_SATURATION</constant></entry>
	    <entry>integer</entry>
	    <entry>Picture color saturation or chroma gain.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CID_HUE</constant></entry>
	    <entry>integer</entry>
	    <entry>Hue or color balance.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CID_AUDIO_VOLUME</constant></entry>
	    <entry>integer</entry>
	    <entry>Overall audio volume. Note some drivers also
provide an OSS or ALSA mixer interface.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CID_AUDIO_BALANCE</constant></entry>
	    <entry>integer</entry>
	    <entry>Audio stereo balance. Minimum corresponds to all
the way left, maximum to right.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CID_AUDIO_BASS</constant></entry>
	    <entry>integer</entry>
	    <entry>Audio bass adjustment.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CID_AUDIO_TREBLE</constant></entry>
	    <entry>integer</entry>
	    <entry>Audio treble adjustment.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CID_AUDIO_MUTE</constant></entry>
	    <entry>boolean</entry>
	    <entry>Mute audio, &ie; set the volume to zero, however
without affecting <constant>V4L2_CID_AUDIO_VOLUME</constant>. Like
ALSA drivers, V4L2 drivers must mute at load time to avoid excessive
noise. Actually the entire device should be reset to a low power
consumption state.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CID_AUDIO_LOUDNESS</constant></entry>
	    <entry>boolean</entry>
	    <entry>Loudness mode (bass boost).</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CID_BLACK_LEVEL</constant></entry>
	    <entry>integer</entry>
	    <entry>Another name for brightness (not a synonym of
<constant>V4L2_CID_BRIGHTNESS</constant>). This control is deprecated
and should not be used in new drivers and applications.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CID_AUTO_WHITE_BALANCE</constant></entry>
	    <entry>boolean</entry>
	    <entry>Automatic white balance (cameras).</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CID_DO_WHITE_BALANCE</constant></entry>
	    <entry>button</entry>
	    <entry>This is an action control. When set (the value is
ignored), the device will do a white balance and then hold the current
setting. Contrast this with the boolean
<constant>V4L2_CID_AUTO_WHITE_BALANCE</constant>, which, when
activated, keeps adjusting the white balance.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CID_RED_BALANCE</constant></entry>
	    <entry>integer</entry>
	    <entry>Red chroma balance.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CID_BLUE_BALANCE</constant></entry>
	    <entry>integer</entry>
	    <entry>Blue chroma balance.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CID_GAMMA</constant></entry>
	    <entry>integer</entry>
	    <entry>Gamma adjust.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CID_WHITENESS</constant></entry>
	    <entry>integer</entry>
	    <entry>Whiteness for grey-scale devices. This is a synonym
for <constant>V4L2_CID_GAMMA</constant>. This control is deprecated
and should not be used in new drivers and applications.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CID_EXPOSURE</constant></entry>
	    <entry>integer</entry>
	    <entry>Exposure (cameras). [Unit?]</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CID_AUTOGAIN</constant></entry>
	    <entry>boolean</entry>
	    <entry>Automatic gain/exposure control.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CID_GAIN</constant></entry>
	    <entry>integer</entry>
	    <entry>Gain control.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CID_HFLIP</constant></entry>
	    <entry>boolean</entry>
	    <entry>Mirror the picture horizontally.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CID_VFLIP</constant></entry>
	    <entry>boolean</entry>
	    <entry>Mirror the picture vertically.</entry>
	  </row>
	<row>
	  <entry><constant>V4L2_CID_HCENTER_DEPRECATED</constant> (formerly <constant>V4L2_CID_HCENTER</constant>)</entry>
	    <entry>integer</entry>
	    <entry>Horizontal image centering. This control is
deprecated. New drivers and applications should use the <link
linkend="camera-controls">Camera class controls</link>
<constant>V4L2_CID_PAN_ABSOLUTE</constant>,
<constant>V4L2_CID_PAN_RELATIVE</constant> and
<constant>V4L2_CID_PAN_RESET</constant> instead.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CID_VCENTER_DEPRECATED</constant>
	    (formerly <constant>V4L2_CID_VCENTER</constant>)</entry>
	    <entry>integer</entry>
	    <entry>Vertical image centering. Centering is intended to
<emphasis>physically</emphasis> adjust cameras. For image cropping see
<xref linkend="crop" />, for clipping <xref linkend="overlay" />. This
control is deprecated. New drivers and applications should use the
<link linkend="camera-controls">Camera class controls</link>
<constant>V4L2_CID_TILT_ABSOLUTE</constant>,
<constant>V4L2_CID_TILT_RELATIVE</constant> and
<constant>V4L2_CID_TILT_RESET</constant> instead.</entry>
	  </row>
	  <row id="v4l2-power-line-frequency">
	    <entry><constant>V4L2_CID_POWER_LINE_FREQUENCY</constant></entry>
	    <entry>enum</entry>
	    <entry>Enables a power line frequency filter to avoid
flicker. Possible values for <constant>enum v4l2_power_line_frequency</constant> are:
<constant>V4L2_CID_POWER_LINE_FREQUENCY_DISABLED</constant> (0),
<constant>V4L2_CID_POWER_LINE_FREQUENCY_50HZ</constant> (1) and
<constant>V4L2_CID_POWER_LINE_FREQUENCY_60HZ</constant> (2).</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CID_HUE_AUTO</constant></entry>
	    <entry>boolean</entry>
	    <entry>Enables automatic hue control by the device. The
effect of setting <constant>V4L2_CID_HUE</constant> while automatic
hue control is enabled is undefined, drivers should ignore such
request.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CID_WHITE_BALANCE_TEMPERATURE</constant></entry>
	    <entry>integer</entry>
	    <entry>This control specifies the white balance settings
as a color temperature in Kelvin. A driver should have a minimum of
2800 (incandescent) to 6500 (daylight). For more information about
color temperature see <ulink
url="http://en.wikipedia.org/wiki/Color_temperature">Wikipedia</ulink>.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CID_SHARPNESS</constant></entry>
	    <entry>integer</entry>
	    <entry>Adjusts the sharpness filters in a camera. The
minimum value disables the filters, higher values give a sharper
picture.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CID_BACKLIGHT_COMPENSATION</constant></entry>
	    <entry>integer</entry>
	    <entry>Adjusts the backlight compensation in a camera. The
minimum value disables backlight compensation.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CID_CHROMA_AGC</constant></entry>
	    <entry>boolean</entry>
	    <entry>Chroma automatic gain control.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CID_CHROMA_GAIN</constant></entry>
	    <entry>integer</entry>
	    <entry>Adjusts the Chroma gain control (for use when chroma AGC
	    is disabled).</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CID_COLOR_KILLER</constant></entry>
	    <entry>boolean</entry>
	    <entry>Enable the color killer (&ie; force a black &amp; white image in case of a weak video signal).</entry>
	  </row>
	  <row id="v4l2-colorfx">
	    <entry><constant>V4L2_CID_COLORFX</constant></entry>
	    <entry>enum</entry>
	    <entry>Selects a color effect. Possible values for
<constant>enum v4l2_colorfx</constant> are:
<constant>V4L2_COLORFX_NONE</constant> (0),
<constant>V4L2_COLORFX_BW</constant> (1),
<constant>V4L2_COLORFX_SEPIA</constant> (2),
<constant>V4L2_COLORFX_NEGATIVE</constant> (3),
<constant>V4L2_COLORFX_EMBOSS</constant> (4),
<constant>V4L2_COLORFX_SKETCH</constant> (5),
<constant>V4L2_COLORFX_SKY_BLUE</constant> (6),
<constant>V4L2_COLORFX_GRASS_GREEN</constant> (7),
<constant>V4L2_COLORFX_SKIN_WHITEN</constant> (8) and
<constant>V4L2_COLORFX_VIVID</constant> (9).</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CID_ROTATE</constant></entry>
	    <entry>integer</entry>
	    <entry>Rotates the image by specified angle. Common angles are 90,
	    270 and 180. Rotating the image to 90 and 270 will reverse the height
	    and width of the display window. It is necessary to set the new height and
	    width of the picture using the &VIDIOC-S-FMT; ioctl according to
	    the rotation angle selected.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CID_BG_COLOR</constant></entry>
	    <entry>integer</entry>
	    <entry>Sets the background color on the current output device.
	    Background color needs to be specified in the RGB24 format. The
	    supplied 32 bit value is interpreted as bits 0-7 Red color information,
	    bits 8-15 Green color information, bits 16-23 Blue color
	    information and bits 24-31 must be zero.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CID_LASTP1</constant></entry>
	    <entry></entry>
	    <entry>End of the predefined control IDs (currently
<constant>V4L2_CID_BG_COLOR</constant> + 1).</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CID_PRIVATE_BASE</constant></entry>
	    <entry></entry>
	    <entry>ID of the first custom (driver specific) control.
Applications depending on particular custom controls should check the
driver name and version, see <xref linkend="querycap" />.</entry>
	  </row>
	</tbody>
      </tgroup>
    </table>

    <para>Applications can enumerate the available controls with the
&VIDIOC-QUERYCTRL; and &VIDIOC-QUERYMENU; ioctls, get and set a
control value with the &VIDIOC-G-CTRL; and &VIDIOC-S-CTRL; ioctls.
Drivers must implement <constant>VIDIOC_QUERYCTRL</constant>,
<constant>VIDIOC_G_CTRL</constant> and
<constant>VIDIOC_S_CTRL</constant> when the device has one or more
controls, <constant>VIDIOC_QUERYMENU</constant> when it has one or
more menu type controls.</para>

    <example>
      <title>Enumerating all controls</title>

      <programlisting>
&v4l2-queryctrl; queryctrl;
&v4l2-querymenu; querymenu;

static void
enumerate_menu (void)
{
	printf ("  Menu items:\n");

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

	for (querymenu.index = queryctrl.minimum;
	     querymenu.index &lt;= queryctrl.maximum;
	      querymenu.index++) {
		if (0 == ioctl (fd, &VIDIOC-QUERYMENU;, &amp;querymenu)) {
			printf ("  %s\n", querymenu.name);
		} else {
			perror ("VIDIOC_QUERYMENU");
			exit (EXIT_FAILURE);
		}
	}
}

memset (&amp;queryctrl, 0, sizeof (queryctrl));

for (queryctrl.id = V4L2_CID_BASE;
     queryctrl.id &lt; V4L2_CID_LASTP1;
     queryctrl.id++) {
	if (0 == ioctl (fd, &VIDIOC-QUERYCTRL;, &amp;queryctrl)) {
		if (queryctrl.flags &amp; V4L2_CTRL_FLAG_DISABLED)
			continue;

		printf ("Control %s\n", queryctrl.name);

		if (queryctrl.type == V4L2_CTRL_TYPE_MENU)
			enumerate_menu ();
	} else {
		if (errno == EINVAL)
			continue;

		perror ("VIDIOC_QUERYCTRL");
		exit (EXIT_FAILURE);
	}
}

for (queryctrl.id = V4L2_CID_PRIVATE_BASE;;
     queryctrl.id++) {
	if (0 == ioctl (fd, &VIDIOC-QUERYCTRL;, &amp;queryctrl)) {
		if (queryctrl.flags &amp; V4L2_CTRL_FLAG_DISABLED)
			continue;

		printf ("Control %s\n", queryctrl.name);

		if (queryctrl.type == V4L2_CTRL_TYPE_MENU)
			enumerate_menu ();
	} else {
		if (errno == EINVAL)
			break;

		perror ("VIDIOC_QUERYCTRL");
		exit (EXIT_FAILURE);
	}
}
</programlisting>
    </example>

    <example>
      <title>Changing controls</title>

      <programlisting>
&v4l2-queryctrl; queryctrl;
&v4l2-control; control;

memset (&amp;queryctrl, 0, sizeof (queryctrl));
queryctrl.id = V4L2_CID_BRIGHTNESS;

if (-1 == ioctl (fd, &VIDIOC-QUERYCTRL;, &amp;queryctrl)) {
	if (errno != EINVAL) {
		perror ("VIDIOC_QUERYCTRL");
		exit (EXIT_FAILURE);
	} else {
		printf ("V4L2_CID_BRIGHTNESS is not supported\n");
	}
} else if (queryctrl.flags &amp; V4L2_CTRL_FLAG_DISABLED) {
	printf ("V4L2_CID_BRIGHTNESS is not supported\n");
} else {
	memset (&amp;control, 0, sizeof (control));
	control.id = V4L2_CID_BRIGHTNESS;
	control.value = queryctrl.default_value;

	if (-1 == ioctl (fd, &VIDIOC-S-CTRL;, &amp;control)) {
		perror ("VIDIOC_S_CTRL");
		exit (EXIT_FAILURE);
	}
}

memset (&amp;control, 0, sizeof (control));
control.id = V4L2_CID_CONTRAST;

if (0 == ioctl (fd, &VIDIOC-G-CTRL;, &amp;control)) {
	control.value += 1;

	/* The driver may clamp the value or return ERANGE, ignored here */

	if (-1 == ioctl (fd, &VIDIOC-S-CTRL;, &amp;control)
	    &amp;&amp; errno != ERANGE) {
		perror ("VIDIOC_S_CTRL");
		exit (EXIT_FAILURE);
	}
/* Ignore if V4L2_CID_CONTRAST is unsupported */
} else if (errno != EINVAL) {
	perror ("VIDIOC_G_CTRL");
	exit (EXIT_FAILURE);
}

control.id = V4L2_CID_AUDIO_MUTE;
control.value = TRUE; /* silence */

/* Errors ignored */
ioctl (fd, VIDIOC_S_CTRL, &amp;control);
</programlisting>
    </example>
  </section>

  <section id="extended-controls">
    <title>Extended Controls</title>

    <section>
      <title>Introduction</title>

      <para>The control mechanism as originally designed was meant
to be used for user settings (brightness, saturation, etc). However,
it turned out to be a very useful model for implementing more
complicated driver APIs where each driver implements only a subset of
a larger API.</para>

      <para>The MPEG encoding API was the driving force behind
designing and implementing this extended control mechanism: the MPEG
standard is quite large and the currently supported hardware MPEG
encoders each only implement a subset of this standard. Further more,
many parameters relating to how the video is encoded into an MPEG
stream are specific to the MPEG encoding chip since the MPEG standard
only defines the format of the resulting MPEG stream, not how the
video is actually encoded into that format.</para>

      <para>Unfortunately, the original control API lacked some
features needed for these new uses and so it was extended into the
(not terribly originally named) extended control API.</para>

      <para>Even though the MPEG encoding API was the first effort
to use the Extended Control API, nowadays there are also other classes
of Extended Controls, such as Camera Controls and FM Transmitter Controls.
The Extended Controls API as well as all Extended Controls classes are
described in the following text.</para>
    </section>

    <section>
      <title>The Extended Control API</title>

      <para>Three new ioctls are available: &VIDIOC-G-EXT-CTRLS;,
&VIDIOC-S-EXT-CTRLS; and &VIDIOC-TRY-EXT-CTRLS;. These ioctls act on
arrays of controls (as opposed to the &VIDIOC-G-CTRL; and
&VIDIOC-S-CTRL; ioctls that act on a single control). This is needed
since it is often required to atomically change several controls at
once.</para>

      <para>Each of the new ioctls expects a pointer to a
&v4l2-ext-controls;. This structure contains a pointer to the control
array, a count of the number of controls in that array and a control
class. Control classes are used to group similar controls into a
single class. For example, control class
<constant>V4L2_CTRL_CLASS_USER</constant> contains all user controls
(&ie; all controls that can also be set using the old
<constant>VIDIOC_S_CTRL</constant> ioctl). Control class
<constant>V4L2_CTRL_CLASS_MPEG</constant> contains all controls
relating to MPEG encoding, etc.</para>

      <para>All controls in the control array must belong to the
specified control class. An error is returned if this is not the
case.</para>

      <para>It is also possible to use an empty control array (count
== 0) to check whether the specified control class is
supported.</para>

      <para>The control array is a &v4l2-ext-control; array. The
<structname>v4l2_ext_control</structname> structure is very similar to
&v4l2-control;, except for the fact that it also allows for 64-bit
values and pointers to be passed.</para>

      <para>It is important to realize that due to the flexibility of
controls it is necessary to check whether the control you want to set
actually is supported in the driver and what the valid range of values
is. So use the &VIDIOC-QUERYCTRL; and &VIDIOC-QUERYMENU; ioctls to
check this. Also note that it is possible that some of the menu
indices in a control of type <constant>V4L2_CTRL_TYPE_MENU</constant>
may not be supported (<constant>VIDIOC_QUERYMENU</constant> will
return an error). A good example is the list of supported MPEG audio
bitrates. Some drivers only support one or two bitrates, others
support a wider range.</para>
    </section>

    <section>
      <title>Enumerating Extended Controls</title>

      <para>The recommended way to enumerate over the extended
controls is by using &VIDIOC-QUERYCTRL; in combination with the
<constant>V4L2_CTRL_FLAG_NEXT_CTRL</constant> flag:</para>

      <informalexample>
	<programlisting>
&v4l2-queryctrl; qctrl;

qctrl.id = V4L2_CTRL_FLAG_NEXT_CTRL;
while (0 == ioctl (fd, &VIDIOC-QUERYCTRL;, &amp;qctrl)) {
	/* ... */
	qctrl.id |= V4L2_CTRL_FLAG_NEXT_CTRL;
}
</programlisting>
      </informalexample>

      <para>The initial control ID is set to 0 ORed with the
<constant>V4L2_CTRL_FLAG_NEXT_CTRL</constant> flag. The
<constant>VIDIOC_QUERYCTRL</constant> ioctl will return the first
control with a higher ID than the specified one. When no such controls
are found an error is returned.</para>

      <para>If you want to get all controls within a specific control
class, then you can set the initial
<structfield>qctrl.id</structfield> value to the control class and add
an extra check to break out of the loop when a control of another
control class is found:</para>

      <informalexample>
	<programlisting>
qctrl.id = V4L2_CTRL_CLASS_MPEG | V4L2_CTRL_FLAG_NEXT_CTRL;
while (0 == ioctl (fd, &VIDIOC-QUERYCTRL;, &amp;qctrl)) {
	if (V4L2_CTRL_ID2CLASS (qctrl.id) != V4L2_CTRL_CLASS_MPEG)
		break;
		/* ... */
		qctrl.id |= V4L2_CTRL_FLAG_NEXT_CTRL;
	}
</programlisting>
      </informalexample>

      <para>The 32-bit <structfield>qctrl.id</structfield> value is
subdivided into three bit ranges: the top 4 bits are reserved for
flags (&eg; <constant>V4L2_CTRL_FLAG_NEXT_CTRL</constant>) and are not
actually part of the ID. The remaining 28 bits form the control ID, of
which the most significant 12 bits define the control class and the
least significant 16 bits identify the control within the control
class. It is guaranteed that these last 16 bits are always non-zero
for controls. The range of 0x1000 and up are reserved for
driver-specific controls. The macro
<constant>V4L2_CTRL_ID2CLASS(id)</constant> returns the control class
ID based on a control ID.</para>

      <para>If the driver does not support extended controls, then
<constant>VIDIOC_QUERYCTRL</constant> will fail when used in
combination with <constant>V4L2_CTRL_FLAG_NEXT_CTRL</constant>. In
that case the old method of enumerating control should be used (see
1.8). But if it is supported, then it is guaranteed to enumerate over
all controls, including driver-private controls.</para>
    </section>

    <section>
      <title>Creating Control Panels</title>

      <para>It is possible to create control panels for a graphical
user interface where the user can select the various controls.
Basically you will have to iterate over all controls using the method
described above. Each control class starts with a control of type
<constant>V4L2_CTRL_TYPE_CTRL_CLASS</constant>.
<constant>VIDIOC_QUERYCTRL</constant> will return the name of this
control class which can be used as the title of a tab page within a
control panel.</para>

      <para>The flags field of &v4l2-queryctrl; also contains hints on
the behavior of the control. See the &VIDIOC-QUERYCTRL; documentation
for more details.</para>
    </section>

    <section id="mpeg-controls">
      <title>MPEG Control Reference</title>

      <para>Below all controls within the MPEG control class are
described. First the generic controls, then controls specific for
certain hardware.</para>

      <section>
	<title>Generic MPEG Controls</title>

	<table pgwide="1" frame="none" id="mpeg-control-id">
	  <title>MPEG Control IDs</title>
	  <tgroup cols="4">
	    <colspec colname="c1" colwidth="1*" />
	    <colspec colname="c2" colwidth="6*" />
	    <colspec colname="c3" colwidth="2*" />
	    <colspec colname="c4" colwidth="6*" />
	    <spanspec namest="c1" nameend="c2" spanname="id" />
	    <spanspec namest="c2" nameend="c4" spanname="descr" />
	    <thead>
	      <row>
		<entry spanname="id" align="left">ID</entry>
		<entry align="left">Type</entry>
	      </row><row rowsep="1"><entry spanname="descr" align="left">Description</entry>
	      </row>
	    </thead>
	    <tbody valign="top">
	      <row><entry></entry></row>
	      <row>
		<entry spanname="id"><constant>V4L2_CID_MPEG_CLASS</constant>&nbsp;</entry>
		<entry>class</entry>
	      </row><row><entry spanname="descr">The MPEG class
descriptor. Calling &VIDIOC-QUERYCTRL; for this control will return a
description of this control class. This description can be used as the
caption of a Tab page in a GUI, for example.</entry>
	      </row>
	      <row><entry></entry></row>
	      <row id="v4l2-mpeg-stream-type">
		<entry spanname="id"><constant>V4L2_CID_MPEG_STREAM_TYPE</constant>&nbsp;</entry>
		<entry>enum&nbsp;v4l2_mpeg_stream_type</entry>
	      </row><row><entry spanname="descr">The MPEG-1, -2 or -4
output stream type. One cannot assume anything here. Each hardware
MPEG encoder tends to support different subsets of the available MPEG
stream types. The currently defined stream types are:</entry>
	      </row>
	      <row>
		<entrytbl spanname="descr" cols="2">
		  <tbody valign="top">
		    <row>
		      <entry><constant>V4L2_MPEG_STREAM_TYPE_MPEG2_PS</constant>&nbsp;</entry>
		      <entry>MPEG-2 program stream</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_STREAM_TYPE_MPEG2_TS</constant>&nbsp;</entry>
		      <entry>MPEG-2 transport stream</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_STREAM_TYPE_MPEG1_SS</constant>&nbsp;</entry>
		      <entry>MPEG-1 system stream</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_STREAM_TYPE_MPEG2_DVD</constant>&nbsp;</entry>
		      <entry>MPEG-2 DVD-compatible stream</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_STREAM_TYPE_MPEG1_VCD</constant>&nbsp;</entry>
		      <entry>MPEG-1 VCD-compatible stream</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_STREAM_TYPE_MPEG2_SVCD</constant>&nbsp;</entry>
		      <entry>MPEG-2 SVCD-compatible stream</entry>
		    </row>
		  </tbody>
		</entrytbl>
	      </row>
	      <row><entry></entry></row>
	      <row>
		<entry spanname="id"><constant>V4L2_CID_MPEG_STREAM_PID_PMT</constant>&nbsp;</entry>
		<entry>integer</entry>
	      </row><row><entry spanname="descr">Program Map Table
Packet ID for the MPEG transport stream (default 16)</entry>
	      </row>
	      <row><entry></entry></row>
	      <row>
		<entry spanname="id"><constant>V4L2_CID_MPEG_STREAM_PID_AUDIO</constant>&nbsp;</entry>
		<entry>integer</entry>
	      </row><row><entry spanname="descr">Audio Packet ID for
the MPEG transport stream (default 256)</entry>
	      </row>
	      <row><entry></entry></row>
	      <row>
		<entry spanname="id"><constant>V4L2_CID_MPEG_STREAM_PID_VIDEO</constant>&nbsp;</entry>
		<entry>integer</entry>
	      </row><row><entry spanname="descr">Video Packet ID for
the MPEG transport stream (default 260)</entry>
	      </row>
	      <row><entry></entry></row>
	      <row>
		<entry spanname="id"><constant>V4L2_CID_MPEG_STREAM_PID_PCR</constant>&nbsp;</entry>
		<entry>integer</entry>
	      </row><row><entry spanname="descr">Packet ID for the
MPEG transport stream carrying PCR fields (default 259)</entry>
	      </row>
	      <row><entry></entry></row>
	      <row>
		<entry spanname="id"><constant>V4L2_CID_MPEG_STREAM_PES_ID_AUDIO</constant>&nbsp;</entry>
		<entry>integer</entry>
	      </row><row><entry spanname="descr">Audio ID for MPEG
PES</entry>
	      </row>
	      <row><entry></entry></row>
	      <row>
		<entry spanname="id"><constant>V4L2_CID_MPEG_STREAM_PES_ID_VIDEO</constant>&nbsp;</entry>
		<entry>integer</entry>
	      </row><row><entry spanname="descr">Video ID for MPEG
PES</entry>
	      </row>
	      <row><entry></entry></row>
	      <row id="v4l2-mpeg-stream-vbi-fmt">
		<entry spanname="id"><constant>V4L2_CID_MPEG_STREAM_VBI_FMT</constant>&nbsp;</entry>
		<entry>enum&nbsp;v4l2_mpeg_stream_vbi_fmt</entry>
	      </row><row><entry spanname="descr">Some cards can embed
VBI data (&eg; Closed Caption, Teletext) into the MPEG stream. This
control selects whether VBI data should be embedded, and if so, what
embedding method should be used. The list of possible VBI formats
depends on the driver. The currently defined VBI format types
are:</entry>
	      </row>
	      <row>
		<entrytbl spanname="descr" cols="2">
		  <tbody valign="top">
		    <row>
		      <entry><constant>V4L2_MPEG_STREAM_VBI_FMT_NONE</constant>&nbsp;</entry>
		      <entry>No VBI in the MPEG stream</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_STREAM_VBI_FMT_IVTV</constant>&nbsp;</entry>
		      <entry>VBI in private packets, IVTV format (documented
in the kernel sources in the file <filename>Documentation/video4linux/cx2341x/README.vbi</filename>)</entry>
		    </row>
		  </tbody>
		</entrytbl>
	      </row>
	      <row><entry></entry></row>
	      <row id="v4l2-mpeg-audio-sampling-freq">
		<entry spanname="id"><constant>V4L2_CID_MPEG_AUDIO_SAMPLING_FREQ</constant>&nbsp;</entry>
		<entry>enum&nbsp;v4l2_mpeg_audio_sampling_freq</entry>
	      </row><row><entry spanname="descr">MPEG Audio sampling
frequency. Possible values are:</entry>
	      </row>
	      <row>
		<entrytbl spanname="descr" cols="2">
		  <tbody valign="top">
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_SAMPLING_FREQ_44100</constant>&nbsp;</entry>
		      <entry>44.1 kHz</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_SAMPLING_FREQ_48000</constant>&nbsp;</entry>
		      <entry>48 kHz</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_SAMPLING_FREQ_32000</constant>&nbsp;</entry>
		      <entry>32 kHz</entry>
		    </row>
		  </tbody>
		</entrytbl>
	      </row>
	      <row><entry></entry></row>
	      <row id="v4l2-mpeg-audio-encoding">
		<entry spanname="id"><constant>V4L2_CID_MPEG_AUDIO_ENCODING</constant>&nbsp;</entry>
		<entry>enum&nbsp;v4l2_mpeg_audio_encoding</entry>
	      </row><row><entry spanname="descr">MPEG Audio encoding.
Possible values are:</entry>
	      </row>
	      <row>
		<entrytbl spanname="descr" cols="2">
		  <tbody valign="top">
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_ENCODING_LAYER_1</constant>&nbsp;</entry>
		      <entry>MPEG-1/2 Layer I encoding</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_ENCODING_LAYER_2</constant>&nbsp;</entry>
		      <entry>MPEG-1/2 Layer II encoding</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_ENCODING_LAYER_3</constant>&nbsp;</entry>
		      <entry>MPEG-1/2 Layer III encoding</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_ENCODING_AAC</constant>&nbsp;</entry>
		      <entry>MPEG-2/4 AAC (Advanced Audio Coding)</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_ENCODING_AC3</constant>&nbsp;</entry>
		      <entry>AC-3 aka ATSC A/52 encoding</entry>
		    </row>
		  </tbody>
		</entrytbl>
	      </row>
	      <row><entry></entry></row>
	      <row id="v4l2-mpeg-audio-l1-bitrate">
		<entry spanname="id"><constant>V4L2_CID_MPEG_AUDIO_L1_BITRATE</constant>&nbsp;</entry>
		<entry>enum&nbsp;v4l2_mpeg_audio_l1_bitrate</entry>
	      </row><row><entry spanname="descr">MPEG-1/2 Layer I bitrate.
Possible values are:</entry>
	      </row>
	      <row>
		<entrytbl spanname="descr" cols="2">
		  <tbody valign="top">
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_L1_BITRATE_32K</constant>&nbsp;</entry>
		      <entry>32 kbit/s</entry></row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_L1_BITRATE_64K</constant>&nbsp;</entry>
		      <entry>64 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_L1_BITRATE_96K</constant>&nbsp;</entry>
		      <entry>96 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_L1_BITRATE_128K</constant>&nbsp;</entry>
		      <entry>128 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_L1_BITRATE_160K</constant>&nbsp;</entry>
		      <entry>160 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_L1_BITRATE_192K</constant>&nbsp;</entry>
		      <entry>192 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_L1_BITRATE_224K</constant>&nbsp;</entry>
		      <entry>224 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_L1_BITRATE_256K</constant>&nbsp;</entry>
		      <entry>256 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_L1_BITRATE_288K</constant>&nbsp;</entry>
		      <entry>288 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_L1_BITRATE_320K</constant>&nbsp;</entry>
		      <entry>320 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_L1_BITRATE_352K</constant>&nbsp;</entry>
		      <entry>352 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_L1_BITRATE_384K</constant>&nbsp;</entry>
		      <entry>384 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_L1_BITRATE_416K</constant>&nbsp;</entry>
		      <entry>416 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_L1_BITRATE_448K</constant>&nbsp;</entry>
		      <entry>448 kbit/s</entry>
		    </row>
		  </tbody>
		</entrytbl>
	      </row>
	      <row><entry></entry></row>
	      <row id="v4l2-mpeg-audio-l2-bitrate">
		<entry spanname="id"><constant>V4L2_CID_MPEG_AUDIO_L2_BITRATE</constant>&nbsp;</entry>
		<entry>enum&nbsp;v4l2_mpeg_audio_l2_bitrate</entry>
	      </row><row><entry spanname="descr">MPEG-1/2 Layer II bitrate.
Possible values are:</entry>
	      </row>
	      <row>
		<entrytbl spanname="descr" cols="2">
		  <tbody valign="top">
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_L2_BITRATE_32K</constant>&nbsp;</entry>
		      <entry>32 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_L2_BITRATE_48K</constant>&nbsp;</entry>
		      <entry>48 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_L2_BITRATE_56K</constant>&nbsp;</entry>
		      <entry>56 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_L2_BITRATE_64K</constant>&nbsp;</entry>
		      <entry>64 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_L2_BITRATE_80K</constant>&nbsp;</entry>
		      <entry>80 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_L2_BITRATE_96K</constant>&nbsp;</entry>
		      <entry>96 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_L2_BITRATE_112K</constant>&nbsp;</entry>
		      <entry>112 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_L2_BITRATE_128K</constant>&nbsp;</entry>
		      <entry>128 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_L2_BITRATE_160K</constant>&nbsp;</entry>
		      <entry>160 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_L2_BITRATE_192K</constant>&nbsp;</entry>
		      <entry>192 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_L2_BITRATE_224K</constant>&nbsp;</entry>
		      <entry>224 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_L2_BITRATE_256K</constant>&nbsp;</entry>
		      <entry>256 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_L2_BITRATE_320K</constant>&nbsp;</entry>
		      <entry>320 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_L2_BITRATE_384K</constant>&nbsp;</entry>
		      <entry>384 kbit/s</entry>
		    </row>
		  </tbody>
		</entrytbl>
	      </row>
	      <row><entry></entry></row>
	      <row id="v4l2-mpeg-audio-l3-bitrate">
		<entry spanname="id"><constant>V4L2_CID_MPEG_AUDIO_L3_BITRATE</constant>&nbsp;</entry>
		<entry>enum&nbsp;v4l2_mpeg_audio_l3_bitrate</entry>
	      </row><row><entry spanname="descr">MPEG-1/2 Layer III bitrate.
Possible values are:</entry>
	      </row>
	      <row>
		<entrytbl spanname="descr" cols="2">
		  <tbody valign="top">
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_L3_BITRATE_32K</constant>&nbsp;</entry>
		      <entry>32 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_L3_BITRATE_40K</constant>&nbsp;</entry>
		      <entry>40 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_L3_BITRATE_48K</constant>&nbsp;</entry>
		      <entry>48 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_L3_BITRATE_56K</constant>&nbsp;</entry>
		      <entry>56 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_L3_BITRATE_64K</constant>&nbsp;</entry>
		      <entry>64 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_L3_BITRATE_80K</constant>&nbsp;</entry>
		      <entry>80 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_L3_BITRATE_96K</constant>&nbsp;</entry>
		      <entry>96 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_L3_BITRATE_112K</constant>&nbsp;</entry>
		      <entry>112 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_L3_BITRATE_128K</constant>&nbsp;</entry>
		      <entry>128 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_L3_BITRATE_160K</constant>&nbsp;</entry>
		      <entry>160 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_L3_BITRATE_192K</constant>&nbsp;</entry>
		      <entry>192 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_L3_BITRATE_224K</constant>&nbsp;</entry>
		      <entry>224 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_L3_BITRATE_256K</constant>&nbsp;</entry>
		      <entry>256 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_L3_BITRATE_320K</constant>&nbsp;</entry>
		      <entry>320 kbit/s</entry>
		    </row>
		  </tbody>
		</entrytbl>
	      </row>
	      <row><entry></entry></row>
	      <row>
		<entry spanname="id"><constant>V4L2_CID_MPEG_AUDIO_AAC_BITRATE</constant>&nbsp;</entry>
		<entry>integer</entry>
	      </row><row><entry spanname="descr">AAC bitrate in bits per second.</entry>
	      </row>
	      <row><entry></entry></row>
	      <row id="v4l2-mpeg-audio-ac3-bitrate">
		<entry spanname="id"><constant>V4L2_CID_MPEG_AUDIO_AC3_BITRATE</constant>&nbsp;</entry>
		<entry>enum&nbsp;v4l2_mpeg_audio_ac3_bitrate</entry>
	      </row><row><entry spanname="descr">AC-3 bitrate.
Possible values are:</entry>
	      </row>
	      <row>
		<entrytbl spanname="descr" cols="2">
		  <tbody valign="top">
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_AC3_BITRATE_32K</constant>&nbsp;</entry>
		      <entry>32 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_AC3_BITRATE_40K</constant>&nbsp;</entry>
		      <entry>40 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_AC3_BITRATE_48K</constant>&nbsp;</entry>
		      <entry>48 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_AC3_BITRATE_56K</constant>&nbsp;</entry>
		      <entry>56 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_AC3_BITRATE_64K</constant>&nbsp;</entry>
		      <entry>64 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_AC3_BITRATE_80K</constant>&nbsp;</entry>
		      <entry>80 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_AC3_BITRATE_96K</constant>&nbsp;</entry>
		      <entry>96 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_AC3_BITRATE_112K</constant>&nbsp;</entry>
		      <entry>112 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_AC3_BITRATE_128K</constant>&nbsp;</entry>
		      <entry>128 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_AC3_BITRATE_160K</constant>&nbsp;</entry>
		      <entry>160 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_AC3_BITRATE_192K</constant>&nbsp;</entry>
		      <entry>192 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_AC3_BITRATE_224K</constant>&nbsp;</entry>
		      <entry>224 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_AC3_BITRATE_256K</constant>&nbsp;</entry>
		      <entry>256 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_AC3_BITRATE_320K</constant>&nbsp;</entry>
		      <entry>320 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_AC3_BITRATE_384K</constant>&nbsp;</entry>
		      <entry>384 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_AC3_BITRATE_448K</constant>&nbsp;</entry>
		      <entry>448 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_AC3_BITRATE_512K</constant>&nbsp;</entry>
		      <entry>512 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_AC3_BITRATE_576K</constant>&nbsp;</entry>
		      <entry>576 kbit/s</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_AC3_BITRATE_640K</constant>&nbsp;</entry>
		      <entry>640 kbit/s</entry>
		    </row>
		  </tbody>
		</entrytbl>
	      </row>
	      <row><entry></entry></row>
	      <row id="v4l2-mpeg-audio-mode">
		<entry spanname="id"><constant>V4L2_CID_MPEG_AUDIO_MODE</constant>&nbsp;</entry>
		<entry>enum&nbsp;v4l2_mpeg_audio_mode</entry>
	      </row><row><entry spanname="descr">MPEG Audio mode.
Possible values are:</entry>
	      </row>
	      <row>
		<entrytbl spanname="descr" cols="2">
		  <tbody valign="top">
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_MODE_STEREO</constant>&nbsp;</entry>
		      <entry>Stereo</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_MODE_JOINT_STEREO</constant>&nbsp;</entry>
		      <entry>Joint Stereo</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_MODE_DUAL</constant>&nbsp;</entry>
		      <entry>Bilingual</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_MODE_MONO</constant>&nbsp;</entry>
		      <entry>Mono</entry>
		    </row>
		  </tbody>
		</entrytbl>
	      </row>
	      <row><entry></entry></row>
	      <row id="v4l2-mpeg-audio-mode-extension">
		<entry spanname="id"><constant>V4L2_CID_MPEG_AUDIO_MODE_EXTENSION</constant>&nbsp;</entry>
		<entry>enum&nbsp;v4l2_mpeg_audio_mode_extension</entry>
	      </row><row><entry spanname="descr">Joint Stereo
audio mode extension. In Layer I and II they indicate which subbands
are in intensity stereo. All other subbands are coded in stereo. Layer
III is not (yet) supported. Possible values
are:</entry>
	      </row>
	      <row>
		<entrytbl spanname="descr" cols="2">
		  <tbody valign="top">
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_MODE_EXTENSION_BOUND_4</constant>&nbsp;</entry>
		      <entry>Subbands 4-31 in intensity stereo</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_MODE_EXTENSION_BOUND_8</constant>&nbsp;</entry>
		      <entry>Subbands 8-31 in intensity stereo</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_MODE_EXTENSION_BOUND_12</constant>&nbsp;</entry>
		      <entry>Subbands 12-31 in intensity stereo</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_MODE_EXTENSION_BOUND_16</constant>&nbsp;</entry>
		      <entry>Subbands 16-31 in intensity stereo</entry>
		    </row>
		  </tbody>
		</entrytbl>
	      </row>
	      <row><entry></entry></row>
	      <row id="v4l2-mpeg-audio-emphasis">
		<entry spanname="id"><constant>V4L2_CID_MPEG_AUDIO_EMPHASIS</constant>&nbsp;</entry>
		<entry>enum&nbsp;v4l2_mpeg_audio_emphasis</entry>
	      </row><row><entry spanname="descr">Audio Emphasis.
Possible values are:</entry>
	      </row>
	      <row>
		<entrytbl spanname="descr" cols="2">
		  <tbody valign="top">
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_EMPHASIS_NONE</constant>&nbsp;</entry>
		      <entry>None</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_EMPHASIS_50_DIV_15_uS</constant>&nbsp;</entry>
		      <entry>50/15 microsecond emphasis</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_EMPHASIS_CCITT_J17</constant>&nbsp;</entry>
		      <entry>CCITT J.17</entry>
		    </row>
		  </tbody>
		</entrytbl>
	      </row>
	      <row><entry></entry></row>
	      <row id="v4l2-mpeg-audio-crc">
		<entry spanname="id"><constant>V4L2_CID_MPEG_AUDIO_CRC</constant>&nbsp;</entry>
		<entry>enum&nbsp;v4l2_mpeg_audio_crc</entry>
	      </row><row><entry spanname="descr">CRC method. Possible
values are:</entry>
	      </row>
	      <row>
		<entrytbl spanname="descr" cols="2">
		  <tbody valign="top">
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_CRC_NONE</constant>&nbsp;</entry>
		      <entry>None</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_AUDIO_CRC_CRC16</constant>&nbsp;</entry>
		      <entry>16 bit parity check</entry>
		    </row>
		  </tbody>
		</entrytbl>
	      </row>
	      <row><entry></entry></row>
	      <row>
		<entry spanname="id"><constant>V4L2_CID_MPEG_AUDIO_MUTE</constant>&nbsp;</entry>
		<entry>boolean</entry>
	      </row><row><entry spanname="descr">Mutes the audio when
capturing. This is not done by muting audio hardware, which can still
produce a slight hiss, but in the encoder itself, guaranteeing a fixed
and reproducable audio bitstream. 0 = unmuted, 1 = muted.</entry>
	      </row>
	      <row><entry></entry></row>
	      <row id="v4l2-mpeg-video-encoding">
		<entry spanname="id"><constant>V4L2_CID_MPEG_VIDEO_ENCODING</constant>&nbsp;</entry>
		<entry>enum&nbsp;v4l2_mpeg_video_encoding</entry>
	      </row><row><entry spanname="descr">MPEG Video encoding
method. Possible values are:</entry>
	      </row>
	      <row>
		<entrytbl spanname="descr" cols="2">
		  <tbody valign="top">
		    <row>
		      <entry><constant>V4L2_MPEG_VIDEO_ENCODING_MPEG_1</constant>&nbsp;</entry>
		      <entry>MPEG-1 Video encoding</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_VIDEO_ENCODING_MPEG_2</constant>&nbsp;</entry>
		      <entry>MPEG-2 Video encoding</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_VIDEO_ENCODING_MPEG_4_AVC</constant>&nbsp;</entry>
		      <entry>MPEG-4 AVC (H.264) Video encoding</entry>
		    </row>
		  </tbody>
		</entrytbl>
	      </row>
	      <row><entry></entry></row>
	      <row id="v4l2-mpeg-video-aspect">
		<entry spanname="id"><constant>V4L2_CID_MPEG_VIDEO_ASPECT</constant>&nbsp;</entry>
		<entry>enum&nbsp;v4l2_mpeg_video_aspect</entry>
	      </row><row><entry spanname="descr">Video aspect.
Possible values are:</entry>
	      </row>
	      <row>
		<entrytbl spanname="descr" cols="2">
		  <tbody valign="top">
		    <row>
		      <entry><constant>V4L2_MPEG_VIDEO_ASPECT_1x1</constant>&nbsp;</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_VIDEO_ASPECT_4x3</constant>&nbsp;</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_VIDEO_ASPECT_16x9</constant>&nbsp;</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_VIDEO_ASPECT_221x100</constant>&nbsp;</entry>
		    </row>
		  </tbody>
		</entrytbl>
	      </row>
	      <row><entry></entry></row>
	      <row>
		<entry spanname="id"><constant>V4L2_CID_MPEG_VIDEO_B_FRAMES</constant>&nbsp;</entry>
		<entry>integer</entry>
	      </row><row><entry spanname="descr">Number of B-Frames
(default 2)</entry>
	      </row>
	      <row><entry></entry></row>
	      <row>
		<entry spanname="id"><constant>V4L2_CID_MPEG_VIDEO_GOP_SIZE</constant>&nbsp;</entry>
		<entry>integer</entry>
	      </row><row><entry spanname="descr">GOP size (default
12)</entry>
	      </row>
	      <row><entry></entry></row>
	      <row>
		<entry spanname="id"><constant>V4L2_CID_MPEG_VIDEO_GOP_CLOSURE</constant>&nbsp;</entry>
		<entry>boolean</entry>
	      </row><row><entry spanname="descr">GOP closure (default
1)</entry>
	      </row>
	      <row><entry></entry></row>
	      <row>
		<entry spanname="id"><constant>V4L2_CID_MPEG_VIDEO_PULLDOWN</constant>&nbsp;</entry>
		<entry>boolean</entry>
	      </row><row><entry spanname="descr">Enable 3:2 pulldown
(default 0)</entry>
	      </row>
	      <row><entry></entry></row>
	      <row id="v4l2-mpeg-video-bitrate-mode">
		<entry spanname="id"><constant>V4L2_CID_MPEG_VIDEO_BITRATE_MODE</constant>&nbsp;</entry>
		<entry>enum&nbsp;v4l2_mpeg_video_bitrate_mode</entry>
	      </row><row><entry spanname="descr">Video bitrate mode.
Possible values are:</entry>
	      </row>
	      <row>
		<entrytbl spanname="descr" cols="2">
		  <tbody valign="top">
		    <row>
		      <entry><constant>V4L2_MPEG_VIDEO_BITRATE_MODE_VBR</constant>&nbsp;</entry>
		      <entry>Variable bitrate</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_VIDEO_BITRATE_MODE_CBR</constant>&nbsp;</entry>
		      <entry>Constant bitrate</entry>
		    </row>
		  </tbody>
		</entrytbl>
	      </row>
	      <row><entry></entry></row>
	      <row>
		<entry spanname="id"><constant>V4L2_CID_MPEG_VIDEO_BITRATE</constant>&nbsp;</entry>
		<entry>integer</entry>
	      </row><row><entry…
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