User ControlsDevices 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.All controls are accessed using an ID value. V4L2 defines
several IDs for specific purposes. Drivers can also implement their
own custom controls using V4L2_CID_PRIVATE_BASE
and higher values. The pre-defined control IDs have the prefix
V4L2_CID_, and are listed in . The ID is used when querying the attributes of
a control, and when getting or setting the current value.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.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
custom ID can also change name and
type.It will be more convenient for applications if drivers
make use of the V4L2_CTRL_FLAG_DISABLED flag, but
that was never required. 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.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.
All controls use machine endianness.
Control IDs
&cs-def;
IDTypeDescriptionV4L2_CID_BASEFirst predefined ID, equal to
V4L2_CID_BRIGHTNESS.V4L2_CID_USER_BASESynonym of V4L2_CID_BASE.V4L2_CID_BRIGHTNESSintegerPicture brightness, or more precisely, the black
level.V4L2_CID_CONTRASTintegerPicture contrast or luma gain.V4L2_CID_SATURATIONintegerPicture color saturation or chroma gain.V4L2_CID_HUEintegerHue or color balance.V4L2_CID_AUDIO_VOLUMEintegerOverall audio volume. Note some drivers also
provide an OSS or ALSA mixer interface.V4L2_CID_AUDIO_BALANCEintegerAudio stereo balance. Minimum corresponds to all
the way left, maximum to right.V4L2_CID_AUDIO_BASSintegerAudio bass adjustment.V4L2_CID_AUDIO_TREBLEintegerAudio treble adjustment.V4L2_CID_AUDIO_MUTEbooleanMute audio, &ie; set the volume to zero, however
without affecting V4L2_CID_AUDIO_VOLUME. 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.V4L2_CID_AUDIO_LOUDNESSbooleanLoudness mode (bass boost).V4L2_CID_BLACK_LEVELintegerAnother name for brightness (not a synonym of
V4L2_CID_BRIGHTNESS). This control is deprecated
and should not be used in new drivers and applications.V4L2_CID_AUTO_WHITE_BALANCEbooleanAutomatic white balance (cameras).V4L2_CID_DO_WHITE_BALANCEbuttonThis 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
V4L2_CID_AUTO_WHITE_BALANCE, which, when
activated, keeps adjusting the white balance.V4L2_CID_RED_BALANCEintegerRed chroma balance.V4L2_CID_BLUE_BALANCEintegerBlue chroma balance.V4L2_CID_GAMMAintegerGamma adjust.V4L2_CID_WHITENESSintegerWhiteness for grey-scale devices. This is a synonym
for V4L2_CID_GAMMA. This control is deprecated
and should not be used in new drivers and applications.V4L2_CID_EXPOSUREintegerExposure (cameras). [Unit?]V4L2_CID_AUTOGAINbooleanAutomatic gain/exposure control.V4L2_CID_GAINintegerGain control.V4L2_CID_HFLIPbooleanMirror the picture horizontally.V4L2_CID_VFLIPbooleanMirror the picture vertically.V4L2_CID_HCENTER_DEPRECATED (formerly V4L2_CID_HCENTER)integerHorizontal image centering. This control is
deprecated. New drivers and applications should use the Camera class controls
V4L2_CID_PAN_ABSOLUTE,
V4L2_CID_PAN_RELATIVE and
V4L2_CID_PAN_RESET instead.V4L2_CID_VCENTER_DEPRECATED
(formerly V4L2_CID_VCENTER)integerVertical image centering. Centering is intended to
physically adjust cameras. For image cropping see
, for clipping . This
control is deprecated. New drivers and applications should use the
Camera class controls
V4L2_CID_TILT_ABSOLUTE,
V4L2_CID_TILT_RELATIVE and
V4L2_CID_TILT_RESET instead.V4L2_CID_POWER_LINE_FREQUENCYenumEnables a power line frequency filter to avoid
flicker. Possible values for enum v4l2_power_line_frequency are:
V4L2_CID_POWER_LINE_FREQUENCY_DISABLED (0),
V4L2_CID_POWER_LINE_FREQUENCY_50HZ (1),
V4L2_CID_POWER_LINE_FREQUENCY_60HZ (2) and
V4L2_CID_POWER_LINE_FREQUENCY_AUTO (3).V4L2_CID_HUE_AUTObooleanEnables automatic hue control by the device. The
effect of setting V4L2_CID_HUE while automatic
hue control is enabled is undefined, drivers should ignore such
request.V4L2_CID_WHITE_BALANCE_TEMPERATUREintegerThis 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 Wikipedia.V4L2_CID_SHARPNESSintegerAdjusts the sharpness filters in a camera. The
minimum value disables the filters, higher values give a sharper
picture.V4L2_CID_BACKLIGHT_COMPENSATIONintegerAdjusts the backlight compensation in a camera. The
minimum value disables backlight compensation.V4L2_CID_CHROMA_AGCbooleanChroma automatic gain control.V4L2_CID_CHROMA_GAINintegerAdjusts the Chroma gain control (for use when chroma AGC
is disabled).V4L2_CID_COLOR_KILLERbooleanEnable the color killer (&ie; force a black & white image in case of a weak video signal).V4L2_CID_COLORFXenumSelects a color effect. The following values are defined:
V4L2_COLORFX_NONEColor effect is disabled.V4L2_COLORFX_ANTIQUEAn aging (old photo) effect.V4L2_COLORFX_ART_FREEZEFrost color effect.V4L2_COLORFX_AQUAWater color, cool tone.V4L2_COLORFX_BWBlack and white.V4L2_COLORFX_EMBOSSEmboss, the highlights and shadows replace light/dark boundaries
and low contrast areas are set to a gray background.V4L2_COLORFX_GRASS_GREENGrass green.V4L2_COLORFX_NEGATIVENegative.V4L2_COLORFX_SEPIASepia tone.V4L2_COLORFX_SKETCHSketch.V4L2_COLORFX_SKIN_WHITENSkin whiten.V4L2_COLORFX_SKY_BLUESky blue.V4L2_COLORFX_SOLARIZATIONSolarization, the image is partially reversed in tone,
only color values above or below a certain threshold are inverted.
V4L2_COLORFX_SILHOUETTESilhouette (outline).V4L2_COLORFX_VIVIDVivid colors.V4L2_COLORFX_SET_CBCRThe Cb and Cr chroma components are replaced by fixed
coefficients determined by V4L2_CID_COLORFX_CBCR
control.V4L2_CID_COLORFX_CBCRintegerDetermines the Cb and Cr coefficients for V4L2_COLORFX_SET_CBCR
color effect. Bits [7:0] of the supplied 32 bit value are interpreted as
Cr component, bits [15:8] as Cb component and bits [31:16] must be zero.
V4L2_CID_ROTATEintegerRotates 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.V4L2_CID_BG_COLORintegerSets 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.V4L2_CID_ILLUMINATORS_1V4L2_CID_ILLUMINATORS_2booleanSwitch on or off the illuminator 1 or 2 of the device
(usually a microscope).V4L2_CID_MIN_BUFFERS_FOR_CAPTUREintegerThis 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.V4L2_CID_MIN_BUFFERS_FOR_OUTPUTintegerThis 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.V4L2_CID_ALPHA_COMPONENTinteger Sets the alpha color component on the capture device or on
the capture buffer queue of a mem-to-mem device. When a mem-to-mem
device produces frame format that includes an alpha component
(e.g. packed RGB image formats)
and the alpha value is not defined by the mem-to-mem input data
this control lets you select the alpha component value of all
pixels. It is applicable to any pixel format that contains an alpha
component.
V4L2_CID_LASTP1End of the predefined control IDs (currently
V4L2_CID_ALPHA_COMPONENT + 1).V4L2_CID_PRIVATE_BASEID of the first custom (driver specific) control.
Applications depending on particular custom controls should check the
driver name and version, see .
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 VIDIOC_QUERYCTRL,
VIDIOC_G_CTRL and
VIDIOC_S_CTRL when the device has one or more
controls, VIDIOC_QUERYMENU when it has one or
more menu type controls.Enumerating all controls
&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);
}
}
Changing controls
&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);
Extended ControlsIntroductionThe 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.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.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.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.The Extended Control APIThree 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.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
V4L2_CTRL_CLASS_USER contains all user controls
(&ie; all controls that can also be set using the old
VIDIOC_S_CTRL ioctl). Control class
V4L2_CTRL_CLASS_MPEG contains all controls
relating to MPEG encoding, etc.All controls in the control array must belong to the
specified control class. An error is returned if this is not the
case.It is also possible to use an empty control array (count
== 0) to check whether the specified control class is
supported.The control array is a &v4l2-ext-control; array. The
v4l2_ext_control structure is very similar to
&v4l2-control;, except for the fact that it also allows for 64-bit
values and pointers to be passed.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 V4L2_CTRL_TYPE_MENU
may not be supported (VIDIOC_QUERYMENU 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.
All controls use machine endianness.
Enumerating Extended ControlsThe recommended way to enumerate over the extended
controls is by using &VIDIOC-QUERYCTRL; in combination with the
V4L2_CTRL_FLAG_NEXT_CTRL flag:
&v4l2-queryctrl; qctrl;
qctrl.id = V4L2_CTRL_FLAG_NEXT_CTRL;
while (0 == ioctl (fd, &VIDIOC-QUERYCTRL;, &qctrl)) {
/* ... */
qctrl.id |= V4L2_CTRL_FLAG_NEXT_CTRL;
}
The initial control ID is set to 0 ORed with the
V4L2_CTRL_FLAG_NEXT_CTRL flag. The
VIDIOC_QUERYCTRL ioctl will return the first
control with a higher ID than the specified one. When no such controls
are found an error is returned.If you want to get all controls within a specific control
class, then you can set the initial
qctrl.id 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:
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;
}
The 32-bit qctrl.id value is
subdivided into three bit ranges: the top 4 bits are reserved for
flags (⪚ V4L2_CTRL_FLAG_NEXT_CTRL) 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
V4L2_CTRL_ID2CLASS(id) returns the control class
ID based on a control ID.If the driver does not support extended controls, then
VIDIOC_QUERYCTRL will fail when used in
combination with V4L2_CTRL_FLAG_NEXT_CTRL. 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.Creating Control PanelsIt 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
V4L2_CTRL_TYPE_CTRL_CLASS.
VIDIOC_QUERYCTRL will return the name of this
control class which can be used as the title of a tab page within a
control panel.The flags field of &v4l2-queryctrl; also contains hints on
the behavior of the control. See the &VIDIOC-QUERYCTRL; documentation
for more details.MPEG Control ReferenceBelow all controls within the MPEG control class are
described. First the generic controls, then controls specific for
certain hardware.Generic MPEG Controls
MPEG Control IDsIDTypeDescriptionV4L2_CID_MPEG_CLASSclassThe 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.V4L2_CID_MPEG_STREAM_TYPEenum v4l2_mpeg_stream_typeThe 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:V4L2_MPEG_STREAM_TYPE_MPEG2_PSMPEG-2 program streamV4L2_MPEG_STREAM_TYPE_MPEG2_TSMPEG-2 transport streamV4L2_MPEG_STREAM_TYPE_MPEG1_SSMPEG-1 system streamV4L2_MPEG_STREAM_TYPE_MPEG2_DVDMPEG-2 DVD-compatible streamV4L2_MPEG_STREAM_TYPE_MPEG1_VCDMPEG-1 VCD-compatible streamV4L2_MPEG_STREAM_TYPE_MPEG2_SVCDMPEG-2 SVCD-compatible streamV4L2_CID_MPEG_STREAM_PID_PMTintegerProgram Map Table
Packet ID for the MPEG transport stream (default 16)V4L2_CID_MPEG_STREAM_PID_AUDIOintegerAudio Packet ID for
the MPEG transport stream (default 256)V4L2_CID_MPEG_STREAM_PID_VIDEOintegerVideo Packet ID for
the MPEG transport stream (default 260)V4L2_CID_MPEG_STREAM_PID_PCRintegerPacket ID for the
MPEG transport stream carrying PCR fields (default 259)V4L2_CID_MPEG_STREAM_PES_ID_AUDIOintegerAudio ID for MPEG
PESV4L2_CID_MPEG_STREAM_PES_ID_VIDEOintegerVideo ID for MPEG
PESV4L2_CID_MPEG_STREAM_VBI_FMTenum v4l2_mpeg_stream_vbi_fmtSome 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:V4L2_MPEG_STREAM_VBI_FMT_NONENo VBI in the MPEG streamV4L2_MPEG_STREAM_VBI_FMT_IVTVVBI in private packets, IVTV format (documented
in the kernel sources in the file Documentation/video4linux/cx2341x/README.vbi)V4L2_CID_MPEG_AUDIO_SAMPLING_FREQenum v4l2_mpeg_audio_sampling_freqMPEG Audio sampling
frequency. Possible values are:V4L2_MPEG_AUDIO_SAMPLING_FREQ_4410044.1 kHzV4L2_MPEG_AUDIO_SAMPLING_FREQ_4800048 kHzV4L2_MPEG_AUDIO_SAMPLING_FREQ_3200032 kHzV4L2_CID_MPEG_AUDIO_ENCODINGenum v4l2_mpeg_audio_encodingMPEG Audio encoding.
This control is specific to multiplexed MPEG streams.
Possible values are:V4L2_MPEG_AUDIO_ENCODING_LAYER_1MPEG-1/2 Layer I encodingV4L2_MPEG_AUDIO_ENCODING_LAYER_2MPEG-1/2 Layer II encodingV4L2_MPEG_AUDIO_ENCODING_LAYER_3MPEG-1/2 Layer III encodingV4L2_MPEG_AUDIO_ENCODING_AACMPEG-2/4 AAC (Advanced Audio Coding)V4L2_MPEG_AUDIO_ENCODING_AC3AC-3 aka ATSC A/52 encodingV4L2_CID_MPEG_AUDIO_L1_BITRATEenum v4l2_mpeg_audio_l1_bitrateMPEG-1/2 Layer I bitrate.
Possible values are:V4L2_MPEG_AUDIO_L1_BITRATE_32K32 kbit/sV4L2_MPEG_AUDIO_L1_BITRATE_64K64 kbit/sV4L2_MPEG_AUDIO_L1_BITRATE_96K96 kbit/sV4L2_MPEG_AUDIO_L1_BITRATE_128K128 kbit/sV4L2_MPEG_AUDIO_L1_BITRATE_160K160 kbit/sV4L2_MPEG_AUDIO_L1_BITRATE_192K192 kbit/sV4L2_MPEG_AUDIO_L1_BITRATE_224K224 kbit/sV4L2_MPEG_AUDIO_L1_BITRATE_256K256 kbit/sV4L2_MPEG_AUDIO_L1_BITRATE_288K288 kbit/sV4L2_MPEG_AUDIO_L1_BITRATE_320K320 kbit/sV4L2_MPEG_AUDIO_L1_BITRATE_352K352 kbit/sV4L2_MPEG_AUDIO_L1_BITRATE_384K384 kbit/sV4L2_MPEG_AUDIO_L1_BITRATE_416K416 kbit/sV4L2_MPEG_AUDIO_L1_BITRATE_448K448 kbit/sV4L2_CID_MPEG_AUDIO_L2_BITRATEenum v4l2_mpeg_audio_l2_bitrateMPEG-1/2 Layer II bitrate.
Possible values are:V4L2_MPEG_AUDIO_L2_BITRATE_32K32 kbit/sV4L2_MPEG_AUDIO_L2_BITRATE_48K48 kbit/sV4L2_MPEG_AUDIO_L2_BITRATE_56K56 kbit/sV4L2_MPEG_AUDIO_L2_BITRATE_64K64 kbit/sV4L2_MPEG_AUDIO_L2_BITRATE_80K80 kbit/sV4L2_MPEG_AUDIO_L2_BITRATE_96K96 kbit/sV4L2_MPEG_AUDIO_L2_BITRATE_112K112 kbit/sV4L2_MPEG_AUDIO_L2_BITRATE_128K128 kbit/sV4L2_MPEG_AUDIO_L2_BITRATE_160K160 kbit/sV4L2_MPEG_AUDIO_L2_BITRATE_192K192 kbit/sV4L2_MPEG_AUDIO_L2_BITRATE_224K224 kbit/sV4L2_MPEG_AUDIO_L2_BITRATE_256K256 kbit/sV4L2_MPEG_AUDIO_L2_BITRATE_320K320 kbit/sV4L2_MPEG_AUDIO_L2_BITRATE_384K384 kbit/sV4L2_CID_MPEG_AUDIO_L3_BITRATEenum v4l2_mpeg_audio_l3_bitrateMPEG-1/2 Layer III bitrate.
Possible values are:V4L2_MPEG_AUDIO_L3_BITRATE_32K32 kbit/sV4L2_MPEG_AUDIO_L3_BITRATE_40K40 kbit/sV4L2_MPEG_AUDIO_L3_BITRATE_48K48 kbit/sV4L2_MPEG_AUDIO_L3_BITRATE_56K56 kbit/sV4L2_MPEG_AUDIO_L3_BITRATE_64K64 kbit/sV4L2_MPEG_AUDIO_L3_BITRATE_80K80 kbit/sV4L2_MPEG_AUDIO_L3_BITRATE_96K96 kbit/sV4L2_MPEG_AUDIO_L3_BITRATE_112K112 kbit/sV4L2_MPEG_AUDIO_L3_BITRATE_128K128 kbit/sV4L2_MPEG_AUDIO_L3_BITRATE_160K160 kbit/sV4L2_MPEG_AUDIO_L3_BITRATE_192K192 kbit/sV4L2_MPEG_AUDIO_L3_BITRATE_224K224 kbit/sV4L2_MPEG_AUDIO_L3_BITRATE_256K256 kbit/sV4L2_MPEG_AUDIO_L3_BITRATE_320K320 kbit/sV4L2_CID_MPEG_AUDIO_AAC_BITRATEintegerAAC bitrate in bits per second.V4L2_CID_MPEG_AUDIO_AC3_BITRATEenum v4l2_mpeg_audio_ac3_bitrateAC-3 bitrate.
Possible values are:V4L2_MPEG_AUDIO_AC3_BITRATE_32K32 kbit/sV4L2_MPEG_AUDIO_AC3_BITRATE_40K40 kbit/sV4L2_MPEG_AUDIO_AC3_BITRATE_48K48 kbit/sV4L2_MPEG_AUDIO_AC3_BITRATE_56K56 kbit/sV4L2_MPEG_AUDIO_AC3_BITRATE_64K64 kbit/sV4L2_MPEG_AUDIO_AC3_BITRATE_80K80 kbit/sV4L2_MPEG_AUDIO_AC3_BITRATE_96K96 kbit/sV4L2_MPEG_AUDIO_AC3_BITRATE_112K112 kbit/sV4L2_MPEG_AUDIO_AC3_BITRATE_128K128 kbit/sV4L2_MPEG_AUDIO_AC3_BITRATE_160K160 kbit/sV4L2_MPEG_AUDIO_AC3_BITRATE_192K192 kbit/sV4L2_MPEG_AUDIO_AC3_BITRATE_224K224 kbit/sV4L2_MPEG_AUDIO_AC3_BITRATE_256K256 kbit/sV4L2_MPEG_AUDIO_AC3_BITRATE_320K320 kbit/sV4L2_MPEG_AUDIO_AC3_BITRATE_384K384 kbit/sV4L2_MPEG_AUDIO_AC3_BITRATE_448K448 kbit/sV4L2_MPEG_AUDIO_AC3_BITRATE_512K512 kbit/sV4L2_MPEG_AUDIO_AC3_BITRATE_576K576 kbit/sV4L2_MPEG_AUDIO_AC3_BITRATE_640K640 kbit/sV4L2_CID_MPEG_AUDIO_MODEenum v4l2_mpeg_audio_modeMPEG Audio mode.
Possible values are:V4L2_MPEG_AUDIO_MODE_STEREOStereoV4L2_MPEG_AUDIO_MODE_JOINT_STEREOJoint StereoV4L2_MPEG_AUDIO_MODE_DUALBilingualV4L2_MPEG_AUDIO_MODE_MONOMonoV4L2_CID_MPEG_AUDIO_MODE_EXTENSIONenum v4l2_mpeg_audio_mode_extensionJoint 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:V4L2_MPEG_AUDIO_MODE_EXTENSION_BOUND_4Subbands 4-31 in intensity stereoV4L2_MPEG_AUDIO_MODE_EXTENSION_BOUND_8Subbands 8-31 in intensity stereoV4L2_MPEG_AUDIO_MODE_EXTENSION_BOUND_12Subbands 12-31 in intensity stereoV4L2_MPEG_AUDIO_MODE_EXTENSION_BOUND_16Subbands 16-31 in intensity stereoV4L2_CID_MPEG_AUDIO_EMPHASISenum v4l2_mpeg_audio_emphasisAudio Emphasis.
Possible values are:V4L2_MPEG_AUDIO_EMPHASIS_NONENoneV4L2_MPEG_AUDIO_EMPHASIS_50_DIV_15_uS50/15 microsecond emphasisV4L2_MPEG_AUDIO_EMPHASIS_CCITT_J17CCITT J.17V4L2_CID_MPEG_AUDIO_CRCenum v4l2_mpeg_audio_crcCRC method. Possible
values are:V4L2_MPEG_AUDIO_CRC_NONENoneV4L2_MPEG_AUDIO_CRC_CRC1616 bit parity checkV4L2_CID_MPEG_AUDIO_MUTEbooleanMutes 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.V4L2_CID_MPEG_AUDIO_DEC_PLAYBACKenum v4l2_mpeg_audio_dec_playbackDetermines how monolingual audio should be played back.
Possible values are:V4L2_MPEG_AUDIO_DEC_PLAYBACK_AUTOAutomatically determines the best playback mode.V4L2_MPEG_AUDIO_DEC_PLAYBACK_STEREOStereo playback.V4L2_MPEG_AUDIO_DEC_PLAYBACK_LEFTLeft channel playback.V4L2_MPEG_AUDIO_DEC_PLAYBACK_RIGHTRight channel playback.V4L2_MPEG_AUDIO_DEC_PLAYBACK_MONOMono playback.V4L2_MPEG_AUDIO_DEC_PLAYBACK_SWAPPED_STEREOStereo playback with swapped left and right channels.V4L2_CID_MPEG_AUDIO_DEC_MULTILINGUAL_PLAYBACKenum v4l2_mpeg_audio_dec_playbackDetermines how multilingual audio should be played back.V4L2_CID_MPEG_VIDEO_ENCODINGenum v4l2_mpeg_video_encodingMPEG Video encoding
method. This control is specific to multiplexed MPEG streams.
Possible values are:V4L2_MPEG_VIDEO_ENCODING_MPEG_1MPEG-1 Video encodingV4L2_MPEG_VIDEO_ENCODING_MPEG_2MPEG-2 Video encodingV4L2_MPEG_VIDEO_ENCODING_MPEG_4_AVCMPEG-4 AVC (H.264) Video encodingV4L2_CID_MPEG_VIDEO_ASPECTenum v4l2_mpeg_video_aspectVideo aspect.
Possible values are:V4L2_MPEG_VIDEO_ASPECT_1x1V4L2_MPEG_VIDEO_ASPECT_4x3V4L2_MPEG_VIDEO_ASPECT_16x9V4L2_MPEG_VIDEO_ASPECT_221x100V4L2_CID_MPEG_VIDEO_B_FRAMESintegerNumber of B-Frames
(default 2)V4L2_CID_MPEG_VIDEO_GOP_SIZEintegerGOP size (default
12)V4L2_CID_MPEG_VIDEO_GOP_CLOSUREbooleanGOP closure (default
1)V4L2_CID_MPEG_VIDEO_PULLDOWNbooleanEnable 3:2 pulldown
(default 0)V4L2_CID_MPEG_VIDEO_BITRATE_MODEenum v4l2_mpeg_video_bitrate_modeVideo bitrate mode.
Possible values are:V4L2_MPEG_VIDEO_BITRATE_MODE_VBRVariable bitrateV4L2_MPEG_VIDEO_BITRATE_MODE_CBRConstant bitrateV4L2_CID_MPEG_VIDEO_BITRATEintegerVideo bitrate in bits
per second.V4L2_CID_MPEG_VIDEO_BITRATE_PEAKintegerPeak 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.V4L2_CID_MPEG_VIDEO_TEMPORAL_DECIMATIONintegerFor every captured
frame, skip this many subsequent frames (default 0).V4L2_CID_MPEG_VIDEO_MUTEboolean"Mutes" the video to a
fixed color when capturing. This is useful for testing, to produce a
fixed video bitstream. 0 = unmuted, 1 = muted.V4L2_CID_MPEG_VIDEO_MUTE_YUVintegerSets the "mute" color
of the video. The supplied 32-bit integer is interpreted as follows (bit
0 = least significant bit):Bit 0:7V chrominance informationBit 8:15U chrominance informationBit 16:23Y luminance informationBit 24:31Must be zero.V4L2_CID_MPEG_VIDEO_DEC_PTSinteger64This read-only control returns the
33-bit video Presentation Time Stamp as defined in ITU T-REC-H.222.0 and ISO/IEC 13818-1 of
the currently displayed frame. This is the same PTS as is used in &VIDIOC-DECODER-CMD;.V4L2_CID_MPEG_VIDEO_DEC_FRAMEinteger64This read-only control returns the
frame counter of the frame that is currently displayed (decoded). This value is reset to 0 whenever
the decoder is started.V4L2_CID_MPEG_VIDEO_DECODER_SLICE_INTERFACEbooleanIf enabled the decoder expects to receive a single slice per buffer, otherwise
the decoder expects a single frame in per buffer. Applicable to the decoder, all codecs.
V4L2_CID_MPEG_VIDEO_H264_VUI_SAR_ENABLEbooleanEnable writing sample aspect ratio in the Video Usability Information.
Applicable to the H264 encoder.V4L2_CID_MPEG_VIDEO_H264_VUI_SAR_IDCenum v4l2_mpeg_video_h264_vui_sar_idcVUI sample aspect ratio indicator for H.264 encoding. The value
is defined in the table E-1 in the standard. Applicable to the H264 encoder.V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_UNSPECIFIEDUnspecifiedV4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_1x11x1V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_12x1112x11V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_10x1110x11V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_16x1116x11V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_40x3340x33V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_24x1124x11V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_20x1120x11V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_32x1132x11V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_80x3380x33V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_18x1118x11V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_15x1115x11V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_64x3364x33V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_160x99160x99V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_4x34x3V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_3x23x2V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_2x12x1V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_EXTENDEDExtended SARV4L2_CID_MPEG_VIDEO_H264_VUI_EXT_SAR_WIDTHintegerExtended sample aspect ratio width for H.264 VUI encoding.
Applicable to the H264 encoder.V4L2_CID_MPEG_VIDEO_H264_VUI_EXT_SAR_HEIGHTintegerExtended sample aspect ratio height for H.264 VUI encoding.
Applicable to the H264 encoder.V4L2_CID_MPEG_VIDEO_H264_LEVELenum v4l2_mpeg_video_h264_levelThe level information for the H264 video elementary stream.
Applicable to the H264 encoder.
Possible values are:V4L2_MPEG_VIDEO_H264_LEVEL_1_0Level 1.0V4L2_MPEG_VIDEO_H264_LEVEL_1BLevel 1BV4L2_MPEG_VIDEO_H264_LEVEL_1_1Level 1.1V4L2_MPEG_VIDEO_H264_LEVEL_1_2Level 1.2V4L2_MPEG_VIDEO_H264_LEVEL_1_3Level 1.3V4L2_MPEG_VIDEO_H264_LEVEL_2_0Level 2.0V4L2_MPEG_VIDEO_H264_LEVEL_2_1Level 2.1V4L2_MPEG_VIDEO_H264_LEVEL_2_2Level 2.2V4L2_MPEG_VIDEO_H264_LEVEL_3_0