path: root/Documentation/DocBook/v4l/controls.xml

  <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_ILLUMINATORS_1</constant>
		<constant>V4L2_CID_ILLUMINATORS_2</constant></entry>
	    <entry>boolean</entry>
	    <entry>Switch on or off the illuminator 1 or 2 of the device
		(usually a microscope).</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_CID_LASTP1</constant></entry>
	    <entry></entry>
	    <entry>End of the predefined control IDs (currently
<constant>V4L2_CID_ILLUMINATORS_2</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);
		}
	}
}

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 reproducible 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 spanname="descr">Video bitrate in bits
per second.</entry>
	      </row>
	      <row><entry></entry></row>
	      <row>
		<entry spanname="id"><constant>V4L2_CID_MPEG_VIDEO_BITRATE_PEAK</constant>&nbsp;</entry>
		<entry>integer</entry>
	      </row><row><entry spanname="descr">Peak video bitrate in
bits per second. Must be larger or equal to the average video bitrate.
It is ignored if the video bitrate mode is set to constant
bitrate.</entry>
	      </row>
	      <row><entry></entry></row>
	      <row>
		<entry spanname="id"><constant>V4L2_CID_MPEG_VIDEO_TEMPORAL_DECIMATION</constant>&nbsp;</entry>
		<entry>integer</entry>
	      </row><row><entry spanname="descr">For every captured
frame, skip this many subsequent frames (default 0).</entry>
	      </row>
	      <row><entry></entry></row>
	      <row>
		<entry spanname="id"><constant>V4L2_CID_MPEG_VIDEO_MUTE</constant>&nbsp;</entry>
		<entry>boolean</entry>
	      </row>
	      <row><entry spanname="descr">"Mutes" the video to a
fixed color when capturing. This is useful for testing, to produce a
fixed video bitstream. 0 = unmuted, 1 = muted.</entry>
	      </row>
	      <row><entry></entry></row>
	      <row>
		<entry spanname="id"><constant>V4L2_CID_MPEG_VIDEO_MUTE_YUV</constant>&nbsp;</entry>
		<entry>integer</entry>
	      </row><row><entry spanname="descr">Sets the "mute" color
of the video. The supplied 32-bit integer is interpreted as follows (bit
0 = least significant bit):</entry>
	      </row>
	      <row>
		<entrytbl spanname="descr" cols="2">
		  <tbody valign="top">
		    <row>
		      <entry>Bit 0:7</entry>
		      <entry>V chrominance information</entry>
		    </row>
		    <row>
		      <entry>Bit 8:15</entry>
		      <entry>U chrominance information</entry>
		    </row>
		    <row>
		      <entry>Bit 16:23</entry>
		      <entry>Y luminance information</entry>
		    </row>
		    <row>
		      <entry>Bit 24:31</entry>
		      <entry>Must be zero.</entry>
		    </row>
		  </tbody>
		</entrytbl>
	      </row>
	    </tbody>
	  </tgroup>
	</table>
      </section>

      <section>
	<title>CX2341x MPEG Controls</title>

	<para>The following MPEG class controls deal with MPEG
encoding settings that are specific to the Conexant CX23415 and
CX23416 MPEG encoding chips.</para>

	<table pgwide="1" frame="none" id="cx2341x-control-id">
	  <title>CX2341x 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><entry spanname="descr" align="left">Description</entry>
	      </row>
	    </thead>
	    <tbody valign="top">
	      <row><entry></entry></row>
	      <row id="v4l2-mpeg-cx2341x-video-spatial-filter-mode">
		<entry spanname="id"><constant>V4L2_CID_MPEG_CX2341X_VIDEO_SPATIAL_FILTER_MODE</constant>&nbsp;</entry>
		<entry>enum&nbsp;v4l2_mpeg_cx2341x_video_spatial_filter_mode</entry>
	      </row><row><entry spanname="descr">Sets the Spatial
Filter mode (default <constant>MANUAL</constant>). Possible values
are:</entry>
	      </row>
	      <row>
		<entrytbl spanname="descr" cols="2">
		  <tbody valign="top">
		    <row>
		      <entry><constant>V4L2_MPEG_CX2341X_VIDEO_SPATIAL_FILTER_MODE_MANUAL</constant>&nbsp;</entry>
		      <entry>Choose the filter manually</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_CX2341X_VIDEO_SPATIAL_FILTER_MODE_AUTO</constant>&nbsp;</entry>
		      <entry>Choose the filter automatically</entry>
		    </row>
		  </tbody>
		</entrytbl>
	      </row>
	      <row><entry></entry></row>
	      <row>
		<entry spanname="id"><constant>V4L2_CID_MPEG_CX2341X_VIDEO_SPATIAL_FILTER</constant>&nbsp;</entry>
		<entry>integer&nbsp;(0-15)</entry>
	      </row><row><entry spanname="descr">The setting for the
Spatial Filter. 0 = off, 15 = maximum. (Default is 0.)</entry>
	      </row>
	      <row><entry></entry></row>
	      <row id="luma-spatial-filter-type">
		<entry spanname="id"><constant>V4L2_CID_MPEG_CX2341X_VIDEO_LUMA_SPATIAL_FILTER_TYPE</constant>&nbsp;</entry>
		<entry>enum&nbsp;v4l2_mpeg_cx2341x_video_luma_spatial_filter_type</entry>
	      </row><row><entry spanname="descr">Select the algorithm
to use for the Luma Spatial Filter (default
<constant>1D_HOR</constant>). Possible values:</entry>
	      </row>
	      <row>
		<entrytbl spanname="descr" cols="2">
		  <tbody valign="top">
		    <row>
		      <entry><constant>V4L2_MPEG_CX2341X_VIDEO_LUMA_SPATIAL_FILTER_TYPE_OFF</constant>&nbsp;</entry>
		      <entry>No filter</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_CX2341X_VIDEO_LUMA_SPATIAL_FILTER_TYPE_1D_HOR</constant>&nbsp;</entry>
		      <entry>One-dimensional horizontal</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_CX2341X_VIDEO_LUMA_SPATIAL_FILTER_TYPE_1D_VERT</constant>&nbsp;</entry>
		      <entry>One-dimensional vertical</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_CX2341X_VIDEO_LUMA_SPATIAL_FILTER_TYPE_2D_HV_SEPARABLE</constant>&nbsp;</entry>
		      <entry>Two-dimensional separable</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_CX2341X_VIDEO_LUMA_SPATIAL_FILTER_TYPE_2D_SYM_NON_SEPARABLE</constant>&nbsp;</entry>
		      <entry>Two-dimensional symmetrical
non-separable</entry>
		    </row>
		  </tbody>
		</entrytbl>
	      </row>
	      <row><entry></entry></row>
	      <row id="chroma-spatial-filter-type">
		<entry spanname="id"><constant>V4L2_CID_MPEG_CX2341X_VIDEO_CHROMA_SPATIAL_FILTER_TYPE</constant>&nbsp;</entry>
		<entry>enum&nbsp;v4l2_mpeg_cx2341x_video_chroma_spatial_filter_type</entry>
	      </row><row><entry spanname="descr">Select the algorithm
for the Chroma Spatial Filter (default <constant>1D_HOR</constant>).
Possible values are:</entry>
	      </row>
	      <row>
		<entrytbl spanname="descr" cols="2">
		  <tbody valign="top">
		    <row>
		      <entry><constant>V4L2_MPEG_CX2341X_VIDEO_CHROMA_SPATIAL_FILTER_TYPE_OFF</constant>&nbsp;</entry>
		      <entry>No filter</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_CX2341X_VIDEO_CHROMA_SPATIAL_FILTER_TYPE_1D_HOR</constant>&nbsp;</entry>
		      <entry>One-dimensional horizontal</entry>
		    </row>
		  </tbody>
		</entrytbl>
	      </row>
	      <row><entry></entry></row>
	      <row id="v4l2-mpeg-cx2341x-video-temporal-filter-mode">
		<entry spanname="id"><constant>V4L2_CID_MPEG_CX2341X_VIDEO_TEMPORAL_FILTER_MODE</constant>&nbsp;</entry>
		<entry>enum&nbsp;v4l2_mpeg_cx2341x_video_temporal_filter_mode</entry>
	      </row><row><entry spanname="descr">Sets the Temporal
Filter mode (default <constant>MANUAL</constant>). Possible values
are:</entry>
	      </row>
	      <row>
		<entrytbl spanname="descr" cols="2">
		  <tbody valign="top">
		    <row>
		      <entry><constant>V4L2_MPEG_CX2341X_VIDEO_TEMPORAL_FILTER_MODE_MANUAL</constant>&nbsp;</entry>
		      <entry>Choose the filter manually</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_CX2341X_VIDEO_TEMPORAL_FILTER_MODE_AUTO</constant>&nbsp;</entry>
		      <entry>Choose the filter automatically</entry>
		    </row>
		  </tbody>
		</entrytbl>
	      </row>
	      <row><entry></entry></row>
	      <row>
		<entry spanname="id"><constant>V4L2_CID_MPEG_CX2341X_VIDEO_TEMPORAL_FILTER</constant>&nbsp;</entry>
		<entry>integer&nbsp;(0-31)</entry>
	      </row><row><entry spanname="descr">The setting for the
Temporal Filter. 0 = off, 31 = maximum. (Default is 8 for full-scale
capturing and 0 for scaled capturing.)</entry>
	      </row>
	      <row><entry></entry></row>
	      <row id="v4l2-mpeg-cx2341x-video-median-filter-type">
		<entry spanname="id"><constant>V4L2_CID_MPEG_CX2341X_VIDEO_MEDIAN_FILTER_TYPE</constant>&nbsp;</entry>
		<entry>enum&nbsp;v4l2_mpeg_cx2341x_video_median_filter_type</entry>
	      </row><row><entry spanname="descr">Median Filter Type
(default <constant>OFF</constant>). Possible values are:</entry>
	      </row>
	      <row>
		<entrytbl spanname="descr" cols="2">
		  <tbody valign="top">
		    <row>
		      <entry><constant>V4L2_MPEG_CX2341X_VIDEO_MEDIAN_FILTER_TYPE_OFF</constant>&nbsp;</entry>
		      <entry>No filter</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_CX2341X_VIDEO_MEDIAN_FILTER_TYPE_HOR</constant>&nbsp;</entry>
		      <entry>Horizontal filter</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_CX2341X_VIDEO_MEDIAN_FILTER_TYPE_VERT</constant>&nbsp;</entry>
		      <entry>Vertical filter</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_CX2341X_VIDEO_MEDIAN_FILTER_TYPE_HOR_VERT</constant>&nbsp;</entry>
		      <entry>Horizontal and vertical filter</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_MPEG_CX2341X_VIDEO_MEDIAN_FILTER_TYPE_DIAG</constant>&nbsp;</entry>
		      <entry>Diagonal filter</entry>
		    </row>
		  </tbody>
		</entrytbl>
	      </row>
	      <row><entry></entry></row>
	      <row>
		<entry spanname="id"><constant>V4L2_CID_MPEG_CX2341X_VIDEO_LUMA_MEDIAN_FILTER_BOTTOM</constant>&nbsp;</entry>
		<entry>integer&nbsp;(0-255)</entry>
	      </row><row><entry spanname="descr">Threshold above which
the luminance median filter is enabled (default 0)</entry>
	      </row>
	      <row><entry></entry></row>
	      <row>
		<entry spanname="id"><constant>V4L2_CID_MPEG_CX2341X_VIDEO_LUMA_MEDIAN_FILTER_TOP</constant>&nbsp;</entry>
		<entry>integer&nbsp;(0-255)</entry>
	      </row><row><entry spanname="descr">Threshold below which
the luminance median filter is enabled (default 255)</entry>
	      </row>
	      <row><entry></entry></row>
	      <row>
		<entry spanname="id"><constant>V4L2_CID_MPEG_CX2341X_VIDEO_CHROMA_MEDIAN_FILTER_BOTTOM</constant>&nbsp;</entry>
		<entry>integer&nbsp;(0-255)</entry>
	      </row><row><entry spanname="descr">Threshold above which
the chroma median filter is enabled (default 0)</entry>
	      </row>
	      <row><entry></entry></row>
	      <row>
		<entry spanname="id"><constant>V4L2_CID_MPEG_CX2341X_VIDEO_CHROMA_MEDIAN_FILTER_TOP</constant>&nbsp;</entry>
		<entry>integer&nbsp;(0-255)</entry>
	      </row><row><entry spanname="descr">Threshold below which
the chroma median filter is enabled (default 255)</entry>
	      </row>
	      <row><entry></entry></row>
	      <row>
		<entry spanname="id"><constant>V4L2_CID_MPEG_CX2341X_STREAM_INSERT_NAV_PACKETS</constant>&nbsp;</entry>
		<entry>boolean</entry>
	      </row>
	      <row><entry spanname="descr">The CX2341X MPEG encoder
can insert one empty MPEG-2 PES packet into the stream between every
four video frames. The packet size is 2048 bytes, including the
packet_start_code_prefix and stream_id fields. The stream_id is 0xBF
(private stream 2). The payload consists of 0x00 bytes, to be filled
in by the application. 0 = do not insert, 1 = insert packets.</entry>
	      </row>
	    </tbody>
	  </tgroup>
	</table>
      </section>
    </section>

    <section id="camera-controls">
      <title>Camera Control Reference</title>

      <para>The Camera class includes controls for mechanical (or
equivalent digital) features of a device such as controllable lenses
or sensors.</para>

    <table pgwide="1" frame="none" id="camera-control-id">
      <title>Camera 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_CAMERA_CLASS</constant>&nbsp;</entry>
	    <entry>class</entry>
	  </row><row><entry spanname="descr">The Camera class
descriptor. Calling &VIDIOC-QUERYCTRL; for this control will return a
description of this control class.</entry>
	  </row>
	  <row><entry></entry></row>

	  <row id="v4l2-exposure-auto-type">
	    <entry spanname="id"><constant>V4L2_CID_EXPOSURE_AUTO</constant>&nbsp;</entry>
	    <entry>enum&nbsp;v4l2_exposure_auto_type</entry>
	  </row><row><entry spanname="descr">Enables automatic
adjustments of the exposure time and/or iris aperture. The effect of
manual changes of the exposure time or iris aperture while these
features are enabled is undefined, drivers should ignore such
requests. Possible values are:</entry>
	  </row>
	  <row>
	    <entrytbl spanname="descr" cols="2">
	      <tbody valign="top">
		<row>
		  <entry><constant>V4L2_EXPOSURE_AUTO</constant>&nbsp;</entry>
		      <entry>Automatic exposure time, automatic iris
aperture.</entry>
		</row>
		<row>
		  <entry><constant>V4L2_EXPOSURE_MANUAL</constant>&nbsp;</entry>
		  <entry>Manual exposure time, manual iris.</entry>
		</row>
		<row>
		  <entry><constant>V4L2_EXPOSURE_SHUTTER_PRIORITY</constant>&nbsp;</entry>
		  <entry>Manual exposure time, auto iris.</entry>
		</row>
		<row>
		  <entry><constant>V4L2_EXPOSURE_APERTURE_PRIORITY</constant>&nbsp;</entry>
		  <entry>Auto exposure time, manual iris.</entry>
		</row>
	      </tbody>
	    </entrytbl>
	  </row>
	  <row><entry></entry></row>

	  <row>
	    <entry spanname="id"><constant>V4L2_CID_EXPOSURE_ABSOLUTE</constant>&nbsp;</entry>
	    <entry>integer</entry>
	  </row><row><entry spanname="descr">Determines the exposure
time of the camera sensor. The exposure time is limited by the frame
interval. Drivers should interpret the values as 100 &micro;s units,
where the value 1 stands for 1/10000th of a second, 10000 for 1 second
and 100000 for 10 seconds.</entry>
	  </row>
	  <row><entry></entry></row>

	  <row>
	    <entry spanname="id"><constant>V4L2_CID_EXPOSURE_AUTO_PRIORITY</constant>&nbsp;</entry>
	    <entry>boolean</entry>
	  </row><row><entry spanname="descr">When
<constant>V4L2_CID_EXPOSURE_AUTO</constant> is set to
<constant>AUTO</constant> or <constant>APERTURE_PRIORITY</constant>,
this control determines if the device may dynamically vary the frame
rate. By default this feature is disabled (0) and the frame rate must
remain constant.</entry>
	  </row>
	  <row><entry></entry></row>

	  <row>
	    <entry spanname="id"><constant>V4L2_CID_PAN_RELATIVE</constant>&nbsp;</entry>
	    <entry>integer</entry>
	  </row><row><entry spanname="descr">This control turns the
camera horizontally by the specified amount. The unit is undefined. A
positive value moves the camera to the right (clockwise when viewed
from above), a negative value to the left. A value of zero does not
cause motion. This is a write-only control.</entry>
	  </row>
	  <row><entry></entry></row>

	  <row>
	    <entry spanname="id"><constant>V4L2_CID_TILT_RELATIVE</constant>&nbsp;</entry>
	    <entry>integer</entry>
	  </row><row><entry spanname="descr">This control turns the
camera vertically by the specified amount. The unit is undefined. A
positive value moves the camera up, a negative value down. A value of
zero does not cause motion. This is a write-only control.</entry>
	  </row>
	  <row><entry></entry></row>

	  <row>
	    <entry spanname="id"><constant>V4L2_CID_PAN_RESET</constant>&nbsp;</entry>
	    <entry>button</entry>
	  </row><row><entry spanname="descr">When this control is set,
the camera moves horizontally to the default position.</entry>
	  </row>
	  <row><entry></entry></row>

	  <row>
	    <entry spanname="id"><constant>V4L2_CID_TILT_RESET</constant>&nbsp;</entry>
	    <entry>button</entry>
	  </row><row><entry spanname="descr">When this control is set,
the camera moves vertically to the default position.</entry>
	  </row>
	  <row><entry></entry></row>

	  <row>
	    <entry spanname="id"><constant>V4L2_CID_PAN_ABSOLUTE</constant>&nbsp;</entry>
	    <entry>integer</entry>
	  </row><row><entry spanname="descr">This control
turns the camera horizontally to the specified position. Positive
values move the camera to the right (clockwise when viewed from above),
negative values to the left. Drivers should interpret the values as arc
seconds, with valid values between -180 * 3600 and +180 * 3600
inclusive.</entry>
	  </row>
	  <row><entry></entry></row>

	  <row>
	    <entry spanname="id"><constant>V4L2_CID_TILT_ABSOLUTE</constant>&nbsp;</entry>
	    <entry>integer</entry>
	  </row><row><entry spanname="descr">This control
turns the camera vertically to the specified position. Positive values
move the camera up, negative values down. Drivers should interpret the
values as arc seconds, with valid values between -180 * 3600 and +180
* 3600 inclusive.</entry>
	  </row>
	  <row><entry></entry></row>

	  <row>
	    <entry spanname="id"><constant>V4L2_CID_FOCUS_ABSOLUTE</constant>&nbsp;</entry>
	    <entry>integer</entry>
	  </row><row><entry spanname="descr">This control sets the
focal point of the camera to the specified position. The unit is
undefined. Positive values set the focus closer to the camera,
negative values towards infinity.</entry>
	  </row>
	  <row><entry></entry></row>

	  <row>
	    <entry spanname="id"><constant>V4L2_CID_FOCUS_RELATIVE</constant>&nbsp;</entry>
	    <entry>integer</entry>
	  </row><row><entry spanname="descr">This control moves the
focal point of the camera by the specified amount. The unit is
undefined. Positive values move the focus closer to the camera,
negative values towards infinity. This is a write-only control.</entry>
	  </row>
	  <row><entry></entry></row>

	  <row>
	    <entry spanname="id"><constant>V4L2_CID_FOCUS_AUTO</constant>&nbsp;</entry>
	    <entry>boolean</entry>
	  </row><row><entry spanname="descr">Enables automatic focus
adjustments. The effect of manual focus adjustments while this feature
is enabled is undefined, drivers should ignore such requests.</entry>
	  </row>
	  <row><entry></entry></row>

	  <row>
	    <entry spanname="id"><constant>V4L2_CID_ZOOM_ABSOLUTE</constant>&nbsp;</entry>
	    <entry>integer</entry>
	  </row><row><entry spanname="descr">Specify the objective lens
focal length as an absolute value. The zoom unit is driver-specific and its
value should be a positive integer.</entry>
	  </row>
	  <row><entry></entry></row>

	  <row>
	    <entry spanname="id"><constant>V4L2_CID_ZOOM_RELATIVE</constant>&nbsp;</entry>
	    <entry>integer</entry>
	  </row><row><entry spanname="descr">Specify the objective lens
focal length relatively to the current value. Positive values move the zoom
lens group towards the telephoto direction, negative values towards the
wide-angle direction. The zoom unit is driver-specific. This is a write-only control.</entry>
	  </row>
	  <row><entry></entry></row>

	  <row>
	    <entry spanname="id"><constant>V4L2_CID_ZOOM_CONTINUOUS</constant>&nbsp;</entry>
	    <entry>integer</entry>
	  </row><row><entry spanname="descr">Move the objective lens group
at the specified speed until it reaches physical device limits or until an
explicit request to stop the movement. A positive value moves the zoom lens
group towards the telephoto direction. A value of zero stops the zoom lens
group movement. A negative value moves the zoom lens group towards the
wide-angle direction. The zoom speed unit is driver-specific.</entry>
	  </row>
	  <row><entry></entry></row>

	  <row>
	    <entry spanname="id"><constant>V4L2_CID_IRIS_ABSOLUTE</constant>&nbsp;</entry>
	    <entry>integer</entry>
	  </row><row><entry spanname="descr">This control sets the
camera's aperture to the specified value. The unit is undefined.
Larger values open the iris wider, smaller values close it.</entry>
	  </row>
	  <row><entry></entry></row>

	  <row>
	    <entry spanname="id"><constant>V4L2_CID_IRIS_RELATIVE</constant>&nbsp;</entry>
	    <entry>integer</entry>
	  </row><row><entry spanname="descr">This control modifies the
camera's aperture by the specified amount. The unit is undefined.
Positive values open the iris one step further, negative values close
it one step further. This is a write-only control.</entry>
	  </row>
	  <row><entry></entry></row>

	  <row>
	    <entry spanname="id"><constant>V4L2_CID_PRIVACY</constant>&nbsp;</entry>
	    <entry>boolean</entry>
	  </row><row><entry spanname="descr">Prevent video from being acquired
by the camera. When this control is set to <constant>TRUE</constant> (1), no
image can be captured by the camera. Common means to enforce privacy are
mechanical obturation of the sensor and firmware image processing, but the
device is not restricted to these methods. Devices that implement the privacy
control must support read access and may support write access.</entry>
	  </row>

	  <row>
	    <entry spanname="id"><constant>V4L2_CID_BAND_STOP_FILTER</constant>&nbsp;</entry>
	    <entry>integer</entry>
	  </row><row><entry spanname="descr">Switch the band-stop filter of a
camera sensor on or off, or specify its strength. Such band-stop filters can
be used, for example, to filter out the fluorescent light component.</entry>
	  </row>
	  <row><entry></entry></row>
	</tbody>
      </tgroup>
    </table>
  </section>

    <section id="fm-tx-controls">
      <title>FM Transmitter Control Reference</title>

      <para>The FM Transmitter (FM_TX) class includes controls for common features of
FM transmissions capable devices. Currently this class includes parameters for audio
compression, pilot tone generation, audio deviation limiter, RDS transmission and
tuning power features.</para>

      <table pgwide="1" frame="none" id="fm-tx-control-id">
      <title>FM_TX 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_FM_TX_CLASS</constant>&nbsp;</entry>
	    <entry>class</entry>
	  </row><row><entry spanname="descr">The FM_TX class
descriptor. Calling &VIDIOC-QUERYCTRL; for this control will return a
description of this control class.</entry>
	  </row>
	  <row>
	    <entry spanname="id"><constant>V4L2_CID_RDS_TX_DEVIATION</constant>&nbsp;</entry>
	    <entry>integer</entry>
	  </row>
	  <row><entry spanname="descr">Configures RDS signal frequency deviation level in Hz.
The range and step are driver-specific.</entry>
	  </row>
	  <row>
	    <entry spanname="id"><constant>V4L2_CID_RDS_TX_PI</constant>&nbsp;</entry>
	    <entry>integer</entry>
	  </row>
	  <row><entry spanname="descr">Sets the RDS Programme Identification field
for transmission.</entry>
	  </row>
	  <row>
	    <entry spanname="id"><constant>V4L2_CID_RDS_TX_PTY</constant>&nbsp;</entry>
	    <entry>integer</entry>
	  </row>
	  <row><entry spanname="descr">Sets the RDS Programme Type field for transmission.
This encodes up to 31 pre-defined programme types.</entry>
	  </row>
	  <row>
	    <entry spanname="id"><constant>V4L2_CID_RDS_TX_PS_NAME</constant>&nbsp;</entry>
	    <entry>string</entry>
	  </row>
	  <row><entry spanname="descr">Sets the Programme Service name (PS_NAME) for transmission.
It is intended for static display on a receiver. It is the primary aid to listeners in programme service
identification and selection.  In Annex E of <xref linkend="en50067" />, the RDS specification,
there is a full description of the correct character encoding for Programme Service name strings.
Also from RDS specification, PS is usually a single eight character text. However, it is also possible
to find receivers which can scroll strings sized as 8 x N characters. So, this control must be configured
with steps of 8 characters. The result is it must always contain a string with size multiple of 8.</entry>
	  </row>
	  <row>
	    <entry spanname="id"><constant>V4L2_CID_RDS_TX_RADIO_TEXT</constant>&nbsp;</entry>
	    <entry>string</entry>
	  </row>
	  <row><entry spanname="descr">Sets the Radio Text info for transmission. It is a textual description of
what is being broadcasted. RDS Radio Text can be applied when broadcaster wishes to transmit longer PS names,
programme-related information or any other text. In these cases, RadioText should be used in addition to
<constant>V4L2_CID_RDS_TX_PS_NAME</constant>. The encoding for Radio Text strings is also fully described
in Annex E of <xref linkend="en50067" />. The length of Radio Text strings depends on which RDS Block is being
used to transmit it, either 32 (2A block) or 64 (2B block).  However, it is also possible
to find receivers which can scroll strings sized as 32 x N or 64 x N characters. So, this control must be configured
with steps of 32 or 64 characters. The result is it must always contain a string with size multiple of 32 or 64. </entry>
	  </row>
	  <row>
	    <entry spanname="id"><constant>V4L2_CID_AUDIO_LIMITER_ENABLED</constant>&nbsp;</entry>
	    <entry>boolean</entry>
	  </row>
	  <row><entry spanname="descr">Enables or disables the audio deviation limiter feature.
The limiter is useful when trying to maximize the audio volume, minimize receiver-generated
distortion and prevent overmodulation.
</entry>
	  </row>
	  <row>
	    <entry spanname="id"><constant>V4L2_CID_AUDIO_LIMITER_RELEASE_TIME</constant>&nbsp;</entry>
	    <entry>integer</entry>
	  </row>
	  <row><entry spanname="descr">Sets the audio deviation limiter feature release time.
Unit is in useconds. Step and range are driver-specific.</entry>
	  </row>
	  <row>
	    <entry spanname="id"><constant>V4L2_CID_AUDIO_LIMITER_DEVIATION</constant>&nbsp;</entry>
	    <entry>integer</entry>
	  </row>
	  <row><entry spanname="descr">Configures audio frequency deviation level in Hz.
The range and step are driver-specific.</entry>
	  </row>
	  <row>
	    <entry spanname="id"><constant>V4L2_CID_AUDIO_COMPRESSION_ENABLED</constant>&nbsp;</entry>
	    <entry>boolean</entry>
	  </row>
	  <row><entry spanname="descr">Enables or disables the audio compression feature.
This feature amplifies signals below the threshold by a fixed gain and compresses audio
signals above the threshold by the ratio of Threshold/(Gain + Threshold).</entry>
	  </row>
	  <row>
	    <entry spanname="id"><constant>V4L2_CID_AUDIO_COMPRESSION_GAIN</constant>&nbsp;</entry>
	    <entry>integer</entry>
	  </row>
	  <row><entry spanname="descr">Sets the gain for audio compression feature. It is
a dB value. The range and step are driver-specific.</entry>
	  </row>
	  <row>
	    <entry spanname="id"><constant>V4L2_CID_AUDIO_COMPRESSION_THRESHOLD</constant>&nbsp;</entry>
	    <entry>integer</entry>
	  </row>
	  <row><entry spanname="descr">Sets the threshold level for audio compression freature.
It is a dB value. The range and step are driver-specific.</entry>
	  </row>
	  <row>
	    <entry spanname="id"><constant>V4L2_CID_AUDIO_COMPRESSION_ATTACK_TIME</constant>&nbsp;</entry>
	    <entry>integer</entry>
	  </row>
	  <row><entry spanname="descr">Sets the attack time for audio compression feature.
It is a useconds value. The range and step are driver-specific.</entry>
	  </row>
	  <row>
	    <entry spanname="id"><constant>V4L2_CID_AUDIO_COMPRESSION_RELEASE_TIME</constant>&nbsp;</entry>
	    <entry>integer</entry>
	  </row>
	  <row><entry spanname="descr">Sets the release time for audio compression feature.
It is a useconds value. The range and step are driver-specific.</entry>
	  </row>
	  <row>
	    <entry spanname="id"><constant>V4L2_CID_PILOT_TONE_ENABLED</constant>&nbsp;</entry>
	    <entry>boolean</entry>
	  </row>
	  <row><entry spanname="descr">Enables or disables the pilot tone generation feature.</entry>
	  </row>
	  <row>
	    <entry spanname="id"><constant>V4L2_CID_PILOT_TONE_DEVIATION</constant>&nbsp;</entry>
	    <entry>integer</entry>
	  </row>
	  <row><entry spanname="descr">Configures pilot tone frequency deviation level. Unit is
in Hz. The range and step are driver-specific.</entry>
	  </row>
	  <row>
	    <entry spanname="id"><constant>V4L2_CID_PILOT_TONE_FREQUENCY</constant>&nbsp;</entry>
	    <entry>integer</entry>
	  </row>
	  <row><entry spanname="descr">Configures pilot tone frequency value. Unit is
in Hz. The range and step are driver-specific.</entry>
	  </row>
	  <row>
	    <entry spanname="id"><constant>V4L2_CID_TUNE_PREEMPHASIS</constant>&nbsp;</entry>
	    <entry>integer</entry>
	  </row>
	  <row id="v4l2-preemphasis"><entry spanname="descr">Configures the pre-emphasis value for broadcasting.
A pre-emphasis filter is applied to the broadcast to accentuate the high audio frequencies.
Depending on the region, a time constant of either 50 or 75 useconds is used. The enum&nbsp;v4l2_preemphasis
defines possible values for pre-emphasis. Here they are:</entry>
	</row><row>
	<entrytbl spanname="descr" cols="2">
		  <tbody valign="top">
		    <row>
		      <entry><constant>V4L2_PREEMPHASIS_DISABLED</constant>&nbsp;</entry>
		      <entry>No pre-emphasis is applied.</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_PREEMPHASIS_50_uS</constant>&nbsp;</entry>
		      <entry>A pre-emphasis of 50 uS is used.</entry>
		    </row>
		    <row>
		      <entry><constant>V4L2_PREEMPHASIS_75_uS</constant>&nbsp;</entry>
		      <entry>A pre-emphasis of 75 uS is used.</entry>
		    </row>
		  </tbody>
		</entrytbl>

	  </row>
	  <row>
	    <entry spanname="id"><constant>V4L2_CID_TUNE_POWER_LEVEL</constant>&nbsp;</entry>
	    <entry>integer</entry>
	  </row>
	  <row><entry spanname="descr">Sets the output power level for signal transmission.
Unit is in dBuV. Range and step are driver-specific.</entry>
	  </row>
	  <row>
	    <entry spanname="id"><constant>V4L2_CID_TUNE_ANTENNA_CAPACITOR</constant>&nbsp;</entry>
	    <entry>integer</entry>
	  </row>
	  <row><entry spanname="descr">This selects the value of antenna tuning capacitor
manually or automatically if set to zero. Unit, range and step are driver-specific.</entry>
	  </row>
	  <row><entry></entry></row>
	</tbody>
      </tgroup>
      </table>

<para>For more details about RDS specification, refer to
<xref linkend="en50067" /> document, from CENELEC.</para>
    </section>
</section>

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