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diff --git a/Documentation/DocBook/media/v4l/controls.xml b/Documentation/DocBook/media/v4l/controls.xml new file mode 100644 index 00000000000..85164016ed2 --- /dev/null +++ b/Documentation/DocBook/media/v4l/controls.xml @@ -0,0 +1,3366 @@ + <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 ⪚ 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> + + <para> + All controls use machine endianness. + </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 & 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_MIN_BUFFERS_FOR_CAPTURE</constant></entry> + <entry>integer</entry> + <entry>This is a read-only control that can be read by the application +and used as a hint to determine the number of CAPTURE buffers to pass to REQBUFS. +The value is the minimum number of CAPTURE buffers that is necessary for hardware +to work.</entry> + </row> + <row> + <entry><constant>V4L2_CID_MIN_BUFFERS_FOR_OUTPUT</constant></entry> + <entry>integer</entry> + <entry>This is a read-only control that can be read by the application +and used as a hint to determine the number of OUTPUT buffers to pass to REQBUFS. +The value is the minimum number of OUTPUT buffers that is necessary for hardware +to work.</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 (&querymenu, 0, sizeof (querymenu)); + querymenu.id = queryctrl.id; + + for (querymenu.index = queryctrl.minimum; + querymenu.index <= queryctrl.maximum; + querymenu.index++) { + if (0 == ioctl (fd, &VIDIOC-QUERYMENU;, &querymenu)) { + printf (" %s\n", querymenu.name); + } + } +} + +memset (&queryctrl, 0, sizeof (queryctrl)); + +for (queryctrl.id = V4L2_CID_BASE; + queryctrl.id < V4L2_CID_LASTP1; + queryctrl.id++) { + if (0 == ioctl (fd, &VIDIOC-QUERYCTRL;, &queryctrl)) { + if (queryctrl.flags & 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;, &queryctrl)) { + if (queryctrl.flags & 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 (&queryctrl, 0, sizeof (queryctrl)); +queryctrl.id = V4L2_CID_BRIGHTNESS; + +if (-1 == ioctl (fd, &VIDIOC-QUERYCTRL;, &queryctrl)) { + if (errno != EINVAL) { + perror ("VIDIOC_QUERYCTRL"); + exit (EXIT_FAILURE); + } else { + printf ("V4L2_CID_BRIGHTNESS is not supported\n"); + } +} else if (queryctrl.flags & V4L2_CTRL_FLAG_DISABLED) { + printf ("V4L2_CID_BRIGHTNESS is not supported\n"); +} else { + memset (&control, 0, sizeof (control)); + control.id = V4L2_CID_BRIGHTNESS; + control.value = queryctrl.default_value; + + if (-1 == ioctl (fd, &VIDIOC-S-CTRL;, &control)) { + perror ("VIDIOC_S_CTRL"); + exit (EXIT_FAILURE); + } +} + +memset (&control, 0, sizeof (control)); +control.id = V4L2_CID_CONTRAST; + +if (0 == ioctl (fd, &VIDIOC-G-CTRL;, &control)) { + control.value += 1; + + /* The driver may clamp the value or return ERANGE, ignored here */ + + if (-1 == ioctl (fd, &VIDIOC-S-CTRL;, &control) + && 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, &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> + + <para> + All controls use machine endianness. + </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;, &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;, &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 (⪚ <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> </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> </entry> + <entry>enum 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. This control is specific to multiplexed MPEG streams. +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> </entry> + <entry>MPEG-2 program stream</entry> + </row> + <row> + <entry><constant>V4L2_MPEG_STREAM_TYPE_MPEG2_TS</constant> </entry> + <entry>MPEG-2 transport stream</entry> + </row> + <row> + <entry><constant>V4L2_MPEG_STREAM_TYPE_MPEG1_SS</constant> </entry> + <entry>MPEG-1 system stream</entry> + </row> + <row> + <entry><constant>V4L2_MPEG_STREAM_TYPE_MPEG2_DVD</constant> </entry> + <entry>MPEG-2 DVD-compatible stream</entry> + </row> + <row> + <entry><constant>V4L2_MPEG_STREAM_TYPE_MPEG1_VCD</constant> </entry> + <entry>MPEG-1 VCD-compatible stream</entry> + </row> + <row> + <entry><constant>V4L2_MPEG_STREAM_TYPE_MPEG2_SVCD</constant> </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> </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> </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> </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> </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> </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> </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> </entry> + <entry>enum v4l2_mpeg_stream_vbi_fmt</entry> + </row><row><entry spanname="descr">Some cards can embed +VBI data (⪚ 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> </entry> + <entry>No VBI in the MPEG stream</entry> + </row> + <row> + <entry><constant>V4L2_MPEG_STREAM_VBI_FMT_IVTV</constant> </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> </entry> + <entry>enum 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> </entry> + <entry>44.1 kHz</entry> + </row> + <row> + <entry><constant>V4L2_MPEG_AUDIO_SAMPLING_FREQ_48000</constant> </entry> + <entry>48 kHz</entry> + </row> + <row> + <entry><constant>V4L2_MPEG_AUDIO_SAMPLING_FREQ_32000</constant> </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> </entry> + <entry>enum v4l2_mpeg_audio_encoding</entry> + </row><row><entry spanname="descr">MPEG Audio encoding. +This control is specific to multiplexed MPEG streams. +Possible values are:</entry> + </row> + <row> + <entrytbl spanname="descr" cols="2"> + <tbody valign="top"> + <row> + <entry><constant>V4L2_MPEG_AUDIO_ENCODING_LAYER_1</constant> </entry> + <entry>MPEG-1/2 Layer I encoding</entry> + </row> + <row> + <entry><constant>V4L2_MPEG_AUDIO_ENCODING_LAYER_2</constant> </entry> + <entry>MPEG-1/2 Layer II encoding</entry> + </row> + <row> + <entry><constant>V4L2_MPEG_AUDIO_ENCODING_LAYER_3</constant> </entry> + <entry>MPEG-1/2 Layer III encoding</entry> + </row> + <row> + <entry><constant>V4L2_MPEG_AUDIO_ENCODING_AAC</constant> </entry> + <entry>MPEG-2/4 AAC (Advanced Audio Coding)</entry> + </row> + <row> + <entry><constant>V4L2_MPEG_AUDIO_ENCODING_AC3</constant> </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> </entry> + <entry>enum v4l2_mpeg_audio_l1_bitrate</entry> + </row><row><entry spanname="descr">MPEG-1/2 Layer I bitrate. +Possible values are:</entry> + </row> |