# User Controls

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.

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 &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. 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;
ID | Type | Description
--- | --- | ---
`V4L2_CID_BASE` |  | First predefined ID, equal to `V4L2_CID_BRIGHTNESS`.
`V4L2_CID_USER_BASE` |  | Synonym of `V4L2_CID_BASE`.
`V4L2_CID_BRIGHTNESS` | integer | Picture brightness, or more precisely, the black level.
`V4L2_CID_CONTRAST` | integer | Picture contrast or luma gain.
`V4L2_CID_SATURATION` | integer | Picture color saturation or chroma gain.
`V4L2_CID_HUE` | integer | Hue or color balance.
`V4L2_CID_AUDIO_VOLUME` | integer | Overall audio volume. Note some drivers also provide an OSS or ALSA mixer interface.
`V4L2_CID_AUDIO_BALANCE` | integer | Audio stereo balance. Minimum corresponds to all the way left, maximum to right.
`V4L2_CID_AUDIO_BASS` | integer | Audio bass adjustment.
`V4L2_CID_AUDIO_TREBLE` | integer | Audio treble adjustment.
`V4L2_CID_AUDIO_MUTE` | boolean | Mute 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_LOUDNESS` | boolean | Loudness mode (bass boost).
`V4L2_CID_BLACK_LEVEL` | integer | Another 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_BALANCE` | boolean | Automatic white balance (cameras).
`V4L2_CID_DO_WHITE_BALANCE` | button | 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 `V4L2_CID_AUTO_WHITE_BALANCE`, which, when activated, keeps adjusting the white balance.
`V4L2_CID_RED_BALANCE` | integer | Red chroma balance.
`V4L2_CID_BLUE_BALANCE` | integer | Blue chroma balance.
`V4L2_CID_GAMMA` | integer | Gamma adjust.
`V4L2_CID_WHITENESS` | integer | Whiteness 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_EXPOSURE` | integer | Exposure (cameras). [Unit?]
`V4L2_CID_AUTOGAIN` | boolean | Automatic gain/exposure control.
`V4L2_CID_GAIN` | integer | Gain control.
`V4L2_CID_HFLIP` | boolean | Mirror the picture horizontally.
`V4L2_CID_VFLIP` | boolean | Mirror the picture vertically.
`V4L2_CID_HCENTER_DEPRECATED` (formerly `V4L2_CID_HCENTER`) | integer | Horizontal 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`) | integer | Vertical 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_FREQUENCY` | enum | Enables 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_AUTO` | boolean | Enables 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_TEMPERATURE` | integer | 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 Wikipedia.
`V4L2_CID_SHARPNESS` | integer | Adjusts the sharpness filters in a camera. The minimum value disables the filters, higher values give a sharper picture.
`V4L2_CID_BACKLIGHT_COMPENSATION` | integer | Adjusts the backlight compensation in a camera. The minimum value disables backlight compensation.
`V4L2_CID_CHROMA_AGC` | boolean | Chroma automatic gain control.
`V4L2_CID_CHROMA_GAIN` | integer | Adjusts the Chroma gain control (for use when chroma AGC is disabled).
`V4L2_CID_COLOR_KILLER` | boolean | Enable the color killer (&ie; force a black & white image in case of a weak video signal).
`V4L2_CID_COLORFX` | enum | Selects a color effect. Possible values for `enum v4l2_colorfx` are: `V4L2_COLORFX_NONE` (0), `V4L2_COLORFX_BW` (1), `V4L2_COLORFX_SEPIA` (2), `V4L2_COLORFX_NEGATIVE` (3), `V4L2_COLORFX_EMBOSS` (4), `V4L2_COLORFX_SKETCH` (5), `V4L2_COLORFX_SKY_BLUE` (6), `V4L2_COLORFX_GRASS_GREEN` (7), `V4L2_COLORFX_SKIN_WHITEN` (8) and `V4L2_COLORFX_VIVID` (9).
`V4L2_CID_ROTATE` | integer | 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.
`V4L2_CID_BG_COLOR` | integer | 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.
`V4L2_CID_ILLUMINATORS_1` `V4L2_CID_ILLUMINATORS_2` | boolean | Switch on or off the illuminator 1 or 2 of the device (usually a microscope).
`V4L2_CID_MIN_BUFFERS_FOR_CAPTURE` | integer | 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.
`V4L2_CID_MIN_BUFFERS_FOR_OUTPUT` | integer | 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.

`V4L2_CID_ALPHA_COMPONENT`

integer

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_LASTP1` |  | End of the predefined control IDs (currently `V4L2_CID_ALPHA_COMPONENT` + 1).
`V4L2_CID_PRIVATE_BASE` |  | ID 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 Controls

## Introduction

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.

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 API

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.

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 Controls

The 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 (&eg; `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 Panels

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 `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 Reference

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

### Generic MPEG Controls

#### MPEG Control IDs

ID | Type
--- | ---
Description
`V4L2_CID_MPEG_CLASS` | class
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.
`V4L2_CID_MPEG_STREAM_TYPE` | enum v4l2_mpeg_stream_type
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:
`V4L2_MPEG_STREAM_TYPE_MPEG2_PS` | MPEG-2 program stream
`V4L2_MPEG_STREAM_TYPE_MPEG2_TS` | MPEG-2 transport stream
`V4L2_MPEG_STREAM_TYPE_MPEG1_SS` | MPEG-1 system stream
`V4L2_MPEG_STREAM_TYPE_MPEG2_DVD` | MPEG-2 DVD-compatible stream
`V4L2_MPEG_STREAM_TYPE_MPEG1_VCD` | MPEG-1 VCD-compatible stream
`V4L2_MPEG_STREAM_TYPE_MPEG2_SVCD` | MPEG-2 SVCD-compatible stream
`V4L2_CID_MPEG_STREAM_PID_PMT` | integer
Program Map Table Packet ID for the MPEG transport stream (default 16)
`V4L2_CID_MPEG_STREAM_PID_AUDIO` | integer
Audio Packet ID for the MPEG transport stream (default 256)
`V4L2_CID_MPEG_STREAM_PID_VIDEO` | integer
Video Packet ID for the MPEG transport stream (default 260)
`V4L2_CID_MPEG_STREAM_PID_PCR` | integer
Packet ID for the MPEG transport stream carrying PCR fields (default 259)
`V4L2_CID_MPEG_STREAM_PES_ID_AUDIO` | integer
Audio ID for MPEG PES
`V4L2_CID_MPEG_STREAM_PES_ID_VIDEO` | integer
Video ID for MPEG PES
`V4L2_CID_MPEG_STREAM_VBI_FMT` | enum v4l2_mpeg_stream_vbi_fmt
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:
`V4L2_MPEG_STREAM_VBI_FMT_NONE` | No VBI in the MPEG stream
`V4L2_MPEG_STREAM_VBI_FMT_IVTV` | VBI in private packets, IVTV format (documented in the kernel sources in the file `Documentation/video4linux/cx2341x/README.vbi`)

V4L2_CID_MPEG_AUDIO_SAMPLING_FREQ
enum v4l2_mpeg_audio_sampling_freq
MPEG Audio sampling frequency. Possible values are:
V4L2_MPEG_AUDIO_SAMPLING_FREQ_44100
44.1 kHz
V4L2_MPEG_AUDIO_SAMPLING_FREQ_48000
48 kHz
V4L2_MPEG_AUDIO_SAMPLING_FREQ_32000
32 kHz
V4L2_CID_MPEG_AUDIO_ENCODING
enum v4l2_mpeg_audio_encoding
MPEG Audio encoding. This control is specific to multiplexed MPEG streams. Possible values are:
V4L2_MPEG_AUDIO_ENCODING_LAYER_1
MPEG-1/2 Layer I encoding
V4L2_MPEG_AUDIO_ENCODING_LAYER_2
MPEG-1/2 Layer II encoding
V4L2_MPEG_AUDIO_ENCODING_LAYER_3
MPEG-1/2 Layer III encoding
V4L2_MPEG_AUDIO_ENCODING_AAC
MPEG-2/4 AAC (Advanced Audio Coding)
V4L2_MPEG_AUDIO_ENCODING_AC3
AC-3 aka ATSC A/52 encoding
V4L2_CID_MPEG_AUDIO_L1_BITRATE
enum v4l2_mpeg_audio_l1_bitrate
MPEG-1/2 Layer I bitrate. Possible values are:
V4L2_MPEG_AUDIO_L1_BITRATE_32K
32 kbit/s
V4L2_MPEG_AUDIO_L1_BITRATE_64K
64 kbit/s
V4L2_MPEG_AUDIO_L1_BITRATE_96K
96 kbit/s
V4L2_MPEG_AUDIO_L1_BITRATE_128K
128 kbit/s
V4L2_MPEG_AUDIO_L1_BITRATE_160K
160 kbit/s
V4L2_MPEG_AUDIO_L1_BITRATE_192K
192 kbit/s
V4L2_MPEG_AUDIO_L1_BITRATE_224K
224 kbit/s
V4L2_MPEG_AUDIO_L1_BITRATE_256K
256 kbit/s
V4L2_MPEG_AUDIO_L1_BITRATE_288K
288 kbit/s
V4L2_MPEG_AUDIO_L1_BITRATE_320K
320 kbit/s
V4L2_MPEG_AUDIO_L1_BITRATE_352K
352 kbit/s
V4L2_MPEG_AUDIO_L1_BITRATE_384K
384 kbit/s
V4L2_MPEG_AUDIO_L1_BITRATE_416K
416 kbit/s
V4L2_MPEG_AUDIO_L1_BITRATE_448K
448 kbit/s
V4L2_CID_MPEG_AUDIO_L2_BITRATE
enum v4l2_mpeg_audio_l2_bitrate
MPEG-1/2 Layer II bitrate. Possible values are:
V4L2_MPEG_AUDIO_L2_BITRATE_32K
32 kbit/s
V4L2_MPEG_AUDIO_L2_BITRATE_48K
48 kbit/s
V4L2_MPEG_AUDIO_L2_BITRATE_56K
56 kbit/s
V4L2_MPEG_AUDIO_L2_BITRATE_64K
64 kbit/s
V4L2_MPEG_AUDIO_L2_BITRATE_80K
80 kbit/s
V4L2_MPEG_AUDIO_L2_BITRATE_96K
96 kbit/s
V4L2_MPEG_AUDIO_L2_BITRATE_112K
112 kbit/s
V4L2_MPEG_AUDIO_L2_BITRATE_128K
128 kbit/s
V4L2_MPEG_AUDIO_L2_BITRATE_160K
160 kbit/s
V4L2_MPEG_AUDIO_L2_BITRATE_192K
192 kbit/s
V4L2_MPEG_AUDIO_L2_BITRATE_224K
224 kbit/s
V4L2_MPEG_AUDIO_L2_BITRATE_256K
256 kbit/s
V4L2_MPEG_AUDIO_L2_BITRATE_320K
320 kbit/s
V4L2_MPEG_AUDIO_L2_BITRATE_384K
384 kbit/s
V4L2_CID_MPEG_AUDIO_L3_BITRATE
enum v4l2_mpeg_audio_l3_bitrate
MPEG-1/2 Layer III bitrate. Possible values are:
V4L2_MPEG_AUDIO_L3_BITRATE_32K
32 kbit/s
V4L2_MPEG_AUDIO_L3_BITRATE_40K
40 kbit/s
V4L2_MPEG_AUDIO_L3_BITRATE_48K
48 kbit/s
V4L2_MPEG_AUDIO_L3_BITRATE_56K
56 kbit/s
V4L2_MPEG_AUDIO_L3_BITRATE_64K
64 kbit/s
V4L2_MPEG_AUDIO_L3_BITRATE_80K
80 kbit/s
V4L2_MPEG_AUDIO_L3_BITRATE_96K
96 kbit/s
V4L2_MPEG_AUDIO_L3_BITRATE_112K
112 kbit/s
V4L2_MPEG_AUDIO_L3_BITRATE_128K
128 kbit/s
V4L2_MPEG_AUDIO_L3_BITRATE_160K
160 kbit/s
V4L2_MPEG_AUDIO_L3_BITRATE_192K
192 kbit/s
V4L2_MPEG_AUDIO_L3_BITRATE_224K
224 kbit/s
V4L2_MPEG_AUDIO_L3_BITRATE_256K
256 kbit/s
V4L2_MPEG_AUDIO_L3_BITRATE_320K
320 kbit/s
V4L2_CID_MPEG_AUDIO_AAC_BITRATE
integer
AAC bitrate in bits per second.
V4L2_CID_MPEG_AUDIO_AC3_BITRATE
enum v4l2_mpeg_audio_ac3_bitrate
AC-3 bitrate. Possible values are:
V4L2_MPEG_AUDIO_AC3_BITRATE_32K
32 kbit/s
V4L2_MPEG_AUDIO_AC3_BITRATE_40K
40 kbit/s
V4L2_MPEG_AUDIO_AC3_BITRATE_48K
48 kbit/s
V4L2_MPEG_AUDIO_AC3_BITRATE_56K
56 kbit/s
V4L2_MPEG_AUDIO_AC3_BITRATE_64K
64 kbit/s
V4L2_MPEG_AUDIO_AC3_BITRATE_80K
80 kbit/s
V4L2_MPEG_AUDIO_AC3_BITRATE_96K
96 kbit/s
V4L2_MPEG_AUDIO_AC3_BITRATE_112K
112 kbit/s
V4L2_MPEG_AUDIO_AC3_BITRATE_128K
128 kbit/s
V4L2_MPEG_AUDIO_AC3_BITRATE_160K
160 kbit/s
V4L2_MPEG_AUDIO_AC3_BITRATE_192K
192 kbit/s
V4L2_MPEG_AUDIO_AC3_BITRATE_224K
224 kbit/s
V4L2_MPEG_AUDIO_AC3_BITRATE_256K
256 kbit/s
V4L2_MPEG_AUDIO_AC3_BITRATE_320K
320 kbit/s
V4L2_MPEG_AUDIO_AC3_BITRATE_384K
384 kbit/s
V4L2_MPEG_AUDIO_AC3_BITRATE_448K
448 kbit/s
V4L2_MPEG_AUDIO_AC3_BITRATE_512K
512 kbit/s
V4L2_MPEG_AUDIO_AC3_BITRATE_576K
576 kbit/s
V4L2_MPEG_AUDIO_AC3_BITRATE_640K
640 kbit/s
V4L2_CID_MPEG_AUDIO_MODE
enum v4l2_mpeg_audio_mode
MPEG Audio mode. Possible values are:
V4L2_MPEG_AUDIO_MODE_STEREO
Stereo
V4L2_MPEG_AUDIO_MODE_JOINT_STEREO
Joint Stereo
V4L2_MPEG_AUDIO_MODE_DUAL
Bilingual
V4L2_MPEG_AUDIO_MODE_MONO
Mono
V4L2_CID_MPEG_AUDIO_MODE_EXTENSION
enum v4l2_mpeg_audio_mode_extension
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:
V4L2_MPEG_AUDIO_MODE_EXTENSION_BOUND_4
Subbands 4-31 in intensity stereo
V4L2_MPEG_AUDIO_MODE_EXTENSION_BOUND_8
Subbands 8-31 in intensity stereo
V4L2_MPEG_AUDIO_MODE_EXTENSION_BOUND_12
Subbands 12-31 in intensity stereo
V4L2_MPEG_AUDIO_MODE_EXTENSION_BOUND_16
Subbands 16-31 in intensity stereo
V4L2_CID_MPEG_AUDIO_EMPHASIS
enum v4l2_mpeg_audio_emphasis
Audio Emphasis. Possible values are:
V4L2_MPEG_AUDIO_EMPHASIS_NONE
None
V4L2_MPEG_AUDIO_EMPHASIS_50_DIV_15_uS
50/15 microsecond emphasis
V4L2_MPEG_AUDIO_EMPHASIS_CCITT_J17
CCITT J.17
V4L2_CID_MPEG_AUDIO_CRC
enum v4l2_mpeg_audio_crc
CRC method. Possible values are:
V4L2_MPEG_AUDIO_CRC_NONE
None
V4L2_MPEG_AUDIO_CRC_CRC16
16 bit parity check
V4L2_CID_MPEG_AUDIO_MUTE
boolean
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.
V4L2_CID_MPEG_AUDIO_DEC_PLAYBACK
enum v4l2_mpeg_audio_dec_playback
Determines how monolingual audio should be played back. Possible values are:
V4L2_MPEG_AUDIO_DEC_PLAYBACK_AUTO
Automatically determines the best playback mode.
V4L2_MPEG_AUDIO_DEC_PLAYBACK_STEREO
Stereo playback.
V4L2_MPEG_AUDIO_DEC_PLAYBACK_LEFT
Left channel playback.
V4L2_MPEG_AUDIO_DEC_PLAYBACK_RIGHT
Right channel playback.
V4L2_MPEG_AUDIO_DEC_PLAYBACK_MONO
Mono playback.
V4L2_MPEG_AUDIO_DEC_PLAYBACK_SWAPPED_STEREO
Stereo playback with swapped left and right channels.
V4L2_CID_MPEG_AUDIO_DEC_MULTILINGUAL_PLAYBACK
enum v4l2_mpeg_audio_dec_playback
Determines how multilingual audio should be played back.
V4L2_CID_MPEG_VIDEO_ENCODING
enum v4l2_mpeg_video_encoding
MPEG Video encoding method. This control is specific to multiplexed MPEG streams. Possible values are:
V4L2_MPEG_VIDEO_ENCODING_MPEG_1
MPEG-1 Video encoding
V4L2_MPEG_VIDEO_ENCODING_MPEG_2
MPEG-2 Video encoding
V4L2_MPEG_VIDEO_ENCODING_MPEG_4_AVC
MPEG-4 AVC (H.264) Video encoding
V4L2_CID_MPEG_VIDEO_ASPECT
enum v4l2_mpeg_video_aspect
Video aspect. Possible values are:
V4L2_MPEG_VIDEO_ASPECT_1x1
V4L2_MPEG_VIDEO_ASPECT_4x3
V4L2_MPEG_VIDEO_ASPECT_16x9
V4L2_MPEG_VIDEO_ASPECT_221x100
V4L2_CID_MPEG_VIDEO_B_FRAMES
integer
Number of B-Frames (default 2)
V4L2_CID_MPEG_VIDEO_GOP_SIZE
integer
GOP size (default 12)
V4L2_CID_MPEG_VIDEO_GOP_CLOSURE
boolean
GOP closure (default 1)
V4L2_CID_MPEG_VIDEO_PULLDOWN
boolean
Enable 3:2 pulldown (default 0)
V4L2_CID_MPEG_VIDEO_BITRATE_MODE
enum v4l2_mpeg_video_bitrate_mode
Video bitrate mode. Possible values are:
V4L2_MPEG_VIDEO_BITRATE_MODE_VBR
Variable bitrate
V4L2_MPEG_VIDEO_BITRATE_MODE_CBR
Constant bitrate
V4L2_CID_MPEG_VIDEO_BITRATE
integer
Video bitrate in bits per second.
V4L2_CID_MPEG_VIDEO_BITRATE_PEAK
integer
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.
V4L2_CID_MPEG_VIDEO_TEMPORAL_DECIMATION
integer
For every captured frame, skip this many subsequent frames (default 0).
V4L2_CID_MPEG_VIDEO_MUTE
boolean
"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_YUV
integer
Sets the "mute" color of the video. The supplied 32-bit integer is interpreted as follows (bit 0 = least significant bit):
Bit 0:7
V chrominance information
Bit 8:15
U chrominance information
Bit 16:23
Y luminance information
Bit 24:31
Must be zero.
V4L2_CID_MPEG_VIDEO_DEC_PTS
integer64
This 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_FRAME
integer64
This 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_INTERFACE
boolean
If 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_ENABLE
boolean
Enable writing sample aspect ratio in the Video Usability Information. Applicable to the H264 encoder.
V4L2_CID_MPEG_VIDEO_H264_VUI_SAR_IDC
enum v4l2_mpeg_video_h264_vui_sar_idc
VUI 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_UNSPECIFIED
Unspecified
V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_1x1
1x1
V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_12x11
12x11
V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_10x11
10x11
V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_16x11
16x11
V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_40x33
40x33
V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_24x11
24x11
V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_20x11
20x11
V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_32x11
32x11
V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_80x33
80x33
V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_18x11
18x11
V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_15x11
15x11
V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_64x33
64x33
V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_160x99
160x99
V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_4x3
4x3
V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_3x2
3x2
V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_2x1
2x1
V4L2_MPEG_VIDEO_H264_VUI_SAR_IDC_EXTENDED
Extended SAR
V4L2_CID_MPEG_VIDEO_H264_VUI_EXT_SAR_WIDTH
integer
Extended sample aspect ratio width for H.264 VUI encoding. Applicable to the H264 encoder.
V4L2_CID_MPEG_VIDEO_H264_VUI_EXT_SAR_HEIGHT
integer
Extended sample aspect ratio height for H.264 VUI encoding. Applicable to the H264 encoder.
V4L2_CID_MPEG_VIDEO_H264_LEVEL
enum v4l2_mpeg_video_h264_level
The level information for the H264 video elementary stream. Applicable to the H264 encoder. Possible values are:
V4L2_MPEG_VIDEO_H264_LEVEL_1_0
Level 1.0
V4L2_MPEG_VIDEO_H264_LEVEL_1B
Level 1B
V4L2_MPEG_VIDEO_H264_LEVEL_1_1
Level 1.1
V4L2_MPEG_VIDEO_H264_LEVEL_1_2
Level 1.2
V4L2_MPEG_VIDEO_H264_LEVEL_1_3
Level 1.3
V4L2_MPEG_VIDEO_H264_LEVEL_2_0
Level 2.0
V4L2_MPEG_VIDEO_H264_LEVEL_2_1
Level 2.1
V4L2_MPEG_VIDEO_H264_LEVEL_2_2
Level 2.2
V4L2_MPEG_VIDEO_H264_LEVEL_3_0
Level 3.0
V4L2_MPEG_VIDEO_H264_LEVEL_3_1
Level 3.1
V4L2_MPEG_VIDEO_H264_LEVEL_3_2
Level 3.2
V4L2_MPEG_VIDEO_H264_LEVEL_4_0
Level 4.0
V4L2_MPEG_VIDEO_H264_LEVEL_4_1
Level 4.1
V4L2_MPEG_VIDEO_H264_LEVEL_4_2
Level 4.2
V4L2_MPEG_VIDEO_H264_LEVEL_5_0
Level 5.0
V4L2_MPEG_VIDEO_H264_LEVEL_5_1
Level 5.1
V4L2_CID_MPEG_VIDEO_MPEG4_LEVEL
enum v4l2_mpeg_video_mpeg4_level
The level information for the MPEG4 elementary stream. Applicable to the MPEG4 encoder. Possible values are:
V4L2_MPEG_VIDEO_LEVEL_0
Level 0
V4L2_MPEG_VIDEO_LEVEL_0B
Level 0b
V4L2_MPEG_VIDEO_LEVEL_1
Level 1
V4L2_MPEG_VIDEO_LEVEL_2
Level 2
V4L2_MPEG_VIDEO_LEVEL_3
Level 3
V4L2_MPEG_VIDEO_LEVEL_3B
Level 3b
V4L2_MPEG_VIDEO_LEVEL_4
Level 4
V4L2_MPEG_VIDEO_LEVEL_5
Level 5
V4L2_CID_MPEG_VIDEO_H264_PROFILE
enum v4l2_mpeg_video_h264_profile
The profile information for H264. Applicable to the H264 encoder. Possible values are:
V4L2_MPEG_VIDEO_H264_PROFILE_BASELINE
Baseline profile
V4L2_MPEG_VIDEO_H264_PROFILE_CONSTRAINED_BASELINE
Constrained Baseline profile
V4L2_MPEG_VIDEO_H264_PROFILE_MAIN
Main profile
V4L2_MPEG_VIDEO_H264_PROFILE_EXTENDED
Extended profile
V4L2_MPEG_VIDEO_H264_PROFILE_HIGH
High profile
V4L2_MPEG_VIDEO_H264_PROFILE_HIGH_10
High 10 profile
V4L2_MPEG_VIDEO_H264_PROFILE_HIGH_422
High 422 profile
V4L2_MPEG_VIDEO_H264_PROFILE_HIGH_444_PREDICTIVE
High 444 Predictive profile
V4L2_MPEG_VIDEO_H264_PROFILE_HIGH_10_INTRA
High 10 Intra profile
V4L2_MPEG_VIDEO_H264_PROFILE_HIGH_422_INTRA
High 422 Intra profile
V4L2_MPEG_VIDEO_H264_PROFILE_HIGH_444_INTRA
High 444 Intra profile
V4L2_MPEG_VIDEO_H264_PROFILE_CAVLC_444_INTRA
CAVLC 444 Intra profile
V4L2_MPEG_VIDEO_H264_PROFILE_SCALABLE_BASELINE
Scalable Baseline profile
V4L2_MPEG_VIDEO_H264_PROFILE_SCALABLE_HIGH
Scalable High profile
V4L2_MPEG_VIDEO_H264_PROFILE_SCALABLE_HIGH_INTRA
Scalable High Intra profile
V4L2_MPEG_VIDEO_H264_PROFILE_STEREO_HIGH
Stereo High profile
V4L2_MPEG_VIDEO_H264_PROFILE_MULTIVIEW_HIGH
Multiview High profile
V4L2_CID_MPEG_VIDEO_MPEG4_PROFILE
enum v4l2_mpeg_video_mpeg4_profile
The profile information for MPEG4. Applicable to the MPEG4 encoder. Possible values are:
V4L2_MPEG_VIDEO_PROFILE_SIMPLE
Simple profile
V4L2_MPEG_VIDEO_PROFILE_ADVANCED_SIMPLE
Advanced Simple profile
V4L2_MPEG_VIDEO_PROFILE_CORE
Core profile
V4L2_MPEG_VIDEO_PROFILE_SIMPLE_SCALABLE
Simple Scalable profile
V4L2_MPEG_VIDEO_PROFILE_ADVANCED_CODING_EFFICIENCY
V4L2_CID_MPEG_VIDEO_MAX_REF_PIC
integer
The maximum number of reference pictures used for encoding. Applicable to the encoder.
V4L2_CID_MPEG_VIDEO_MULTI_SLICE_MODE
enum v4l2_mpeg_video_multi_slice_mode
Determines how the encoder should handle division of frame into slices. Applicable to the encoder. Possible values are:
V4L2_MPEG_VIDEO_MULTI_SLICE_MODE_SINGLE
Single slice per frame.
V4L2_MPEG_VIDEO_MULTI_SLICE_MODE_MAX_MB
Multiple slices with set maximum number of macroblocks per slice.
V4L2_MPEG_VIDEO_MULTI_SLICE_MODE_MAX_BYTES
Multiple slice with set maximum size in bytes per slice.
V4L2_CID_MPEG_VIDEO_MULTI_SLICE_MAX_MB
integer
The maximum number of macroblocks in a slice. Used when `V4L2_CID_MPEG_VIDEO_MULTI_SLICE_MODE` is set to `V4L2_MPEG_VIDEO_MULTI_SLICE_MODE_MAX_MB`. Applicable to the encoder.
V4L2_CID_MPEG_VIDEO_MULTI_SLICE_MAX_BYTES
integer
The maximum size of a slice in bytes. Used when `V4L2_CID_MPEG_VIDEO_MULTI_SLICE_MODE` is set to `V4L2_MPEG_VIDEO_MULTI_SLICE_MODE_MAX_BYTES`. Applicable to the encoder.
V4L2_CID_MPEG_VIDEO_H264_LOOP_FILTER_MODE
enum v4l2_mpeg_video_h264_loop_filter_mode
Loop filter mode for H264 encoder. Possible values are:
V4L2_MPEG_VIDEO_H264_LOOP_FILTER_MODE_ENABLED
Loop filter is enabled.
V4L2_MPEG_VIDEO_H264_LOOP_FILTER_MODE_DISABLED
Loop filter is disabled.
V4L2_MPEG_VIDEO_H264_LOOP_FILTER_MODE_DISABLED_AT_SLICE_BOUNDARY
Loop filter is disabled at the slice boundary.
V4L2_CID_MPEG_VIDEO_H264_LOOP_FILTER_ALPHA
integer
Loop filter alpha coefficient, defined in the H264 standard. Applicable to the H264 encoder.
V4L2_CID_MPEG_VIDEO_H264_LOOP_FILTER_BETA
integer
Loop filter beta coefficient, defined in the H264 standard. Applicable to the H264 encoder.
V4L2_CID_MPEG_VIDEO_H264_ENTROPY_MODE
enum v4l2_mpeg_video_h264_entropy_mode
Entropy coding mode for H264 - CABAC/CAVALC. Applicable to the H264 encoder. Possible values are:
V4L2_MPEG_VIDEO_H264_ENTROPY_MODE_CAVLC
Use CAVLC entropy coding.
V4L2_MPEG_VIDEO_H264_ENTROPY_MODE_CABAC
Use CABAC entropy coding.
V4L2_CID_MPEG_VIDEO_H264_8X8_TRANSFORM
boolean
Enable 8X8 transform for H264. Applicable to the H264 encoder.
V4L2_CID_MPEG_VIDEO_CYCLIC_INTRA_REFRESH_MB
integer
Cyclic intra macroblock refresh. This is the number of continuous macroblocks refreshed every frame. Each frame a succesive set of macroblocks is refreshed until the cycle completes and starts from the top of the frame. Applicable to H264, H263 and MPEG4 encoder.
V4L2_CID_MPEG_VIDEO_FRAME_RC_ENABLE
boolean
Frame level rate control enable. If this control is disabled then the quantization parameter for each frame type is constant and set with appropriate controls (e.g. `V4L2_CID_MPEG_VIDEO_H263_I_FRAME_QP`). If frame rate control is enabled then quantization parameter is adjusted to meet the chosen bitrate. Minimum and maximum value for the quantization parameter can be set with appropriate controls (e.g. `V4L2_CID_MPEG_VIDEO_H263_MIN_QP`). Applicable to encoders.
V4L2_CID_MPEG_VIDEO_MB_RC_ENABLE
boolean
Macroblock level rate control enable. Applicable to the MPEG4 and H264 encoders.
V4L2_CID_MPEG_VIDEO_MPEG4_QPEL
boolean
Quarter pixel motion estimation for MPEG4. Applicable to the MPEG4 encoder.
V4L2_CID_MPEG_VIDEO_H263_I_FRAME_QP
integer
Quantization parameter for an I frame for H263. Valid range: from 1 to 31.
V4L2_CID_MPEG_VIDEO_H263_MIN_QP
integer
Minimum quantization parameter for H263. Valid range: from 1 to 31.
V4L2_CID_MPEG_VIDEO_H263_MAX_QP
integer
Maximum quantization parameter for H263. Valid range: from 1 to 31.
V4L2_CID_MPEG_VIDEO_H263_P_FRAME_QP
integer
Quantization parameter for an P frame for H263. Valid range: from 1 to 31.
V4L2_CID_MPEG_VIDEO_H263_B_FRAME_QP
integer
Quantization parameter for an B frame for H263. Valid range: from 1 to 31.
V4L2_CID_MPEG_VIDEO_H264_I_FRAME_QP
integer
Quantization parameter for an I frame for H264. Valid range: from 0 to 51.
V4L2_CID_MPEG_VIDEO_H264_MIN_QP
integer
Minimum quantization parameter for H264. Valid range: from 0 to 51.
V4L2_CID_MPEG_VIDEO_H264_MAX_QP
integer
Maximum quantization parameter for H264. Valid range: from 0 to 51.
V4L2_CID_MPEG_VIDEO_H264_P_FRAME_QP
integer
Quantization parameter for an P frame for H264. Valid range: from 0 to 51.
V4L2_CID_MPEG_VIDEO_H264_B_FRAME_QP
integer
Quantization parameter for an B frame for H264. Valid range: from 0 to 51.
V4L2_CID_MPEG_VIDEO_MPEG4_I_FRAME_QP
integer
Quantization parameter for an I frame for MPEG4. Valid range: from 1 to 31.
V4L2_CID_MPEG_VIDEO_MPEG4_MIN_QP
integer
Minimum quantization parameter for MPEG4. Valid range: from 1 to 31.
V4L2_CID_MPEG_VIDEO_MPEG4_MAX_QP
integer
Maximum quantization parameter for MPEG4. Valid range: from 1 to 31.
V4L2_CID_MPEG_VIDEO_MPEG4_P_FRAME_QP
integer
Quantization parameter for an P frame for MPEG4. Valid range: from 1 to 31.
V4L2_CID_MPEG_VIDEO_MPEG4_B_FRAME_QP
integer
Quantization parameter for an B frame for MPEG4. Valid range: from 1 to 31.
V4L2_CID_MPEG_VIDEO_VBV_SIZE
integer
The Video Buffer Verifier size in kilobytes, it is used as a limitation of frame skip. The VBV is defined in the standard as a mean to verify that the produced stream will be succesfully decoded. The standard describes it as "Part of a hypothetical decoder that is conceptually connected to the output of the encoder. Its purpose is to provide a constraint on the variability of the data rate that an encoder or editing process may produce.". Applicable to the MPEG1, MPEG2, MPEG4 encoders.
V4L2_CID_MPEG_VIDEO_H264_CPB_SIZE
integer
The Coded Picture Buffer size in kilobytes, it is used as a limitation of frame skip. The CPB is defined in the H264 standard as a mean to verify that the produced stream will be succesfully decoded. Applicable to the H264 encoder.
V4L2_CID_MPEG_VIDEO_H264_I_PERIOD
integer
Period between I-frames in the open GOP for H264. In case of an open GOP this is the period between two I-frames. The period between IDR (Instantaneous Decoding Refresh) frames is taken from the GOP_SIZE control. An IDR frame, which stands for Instantaneous Decoding Refresh is an I-frame after which no prior frames are referenced. This means that a stream can be restarted from an IDR frame without the need to store or decode any previous frames. Applicable to the H264 encoder.
V4L2_CID_MPEG_VIDEO_HEADER_MODE
enum v4l2_mpeg_video_header_mode
Determines whether the header is returned as the first buffer or is it returned together with the first frame. Applicable to encoders. Possible values are:
V4L2_MPEG_VIDEO_HEADER_MODE_SEPARATE
The stream header is returned separately in the first buffer.
V4L2_MPEG_VIDEO_HEADER_MODE_JOINED_WITH_1ST_FRAME
The stream header is returned together with the first encoded frame.
V4L2_CID_MPEG_VIDEO_DECODER_MPEG4_DEBLOCK_FILTER
boolean
Enabled the deblocking post processing filter for MPEG4 decoder. Applicable to the MPEG4 decoder.
V4L2_CID_MPEG_VIDEO_MPEG4_VOP_TIME_RES
integer
vop_time_increment_resolution value for MPEG4. Applicable to the MPEG4 encoder.
V4L2_CID_MPEG_VIDEO_MPEG4_VOP_TIME_INC
integer
vop_time_increment value for MPEG4. Applicable to the MPEG4 encoder.

### MFC 5.1 MPEG Controls

The following MPEG class controls deal with MPEG decoding and encoding settings that are specific to the Multi Format Codec 5.1 device present in the S5P family of SoCs by Samsung.

#### MFC 5.1 Control IDs

ID | Type
--- | ---
Description
`V4L2_CID_MPEG_MFC51_VIDEO_DECODER_H264_DISPLAY_DELAY_ENABLE` | integer

If the display delay is enabled then the decoder has to return a CAPTURE buffer after processing a certain number of OUTPUT buffers. If this number is low, then it may result in buffers not being dequeued in display order. In addition hardware may still use those buffers as reference, thus application should not write to those buffers. This feature can be used for example for generating thumbnails of videos. Applicable to the H264 decoder.

`V4L2_CID_MPEG_MFC51_VIDEO_DECODER_H264_DISPLAY_DELAY` | integer
Display delay value for H264 decoder. The decoder is forced to return a decoded frame after the set 'display delay' number of frames. If this number is low it may result in frames returned out of dispaly order, in addition the hardware may still be using the returned buffer as a reference picture for subsequent frames.
`V4L2_CID_MPEG_MFC51_VIDEO_H264_NUM_REF_PIC_FOR_P` | integer
The number of reference pictures used for encoding a P picture. Applicable to the H264 encoder.
`V4L2_CID_MPEG_MFC51_VIDEO_PADDING` | boolean
Padding enable in the encoder - use a color instead of repeating border pixels. Applicable to encoders.
`V4L2_CID_MPEG_MFC51_VIDEO_PADDING_YUV` | integer
Padding color in the encoder. Applicable to encoders. The supplied 32-bit integer is interpreted as follows (bit 0 = least significant bit):
Bit 0:7 | V chrominance information
Bit 8:15 | U chrominance information
Bit 16:23 | Y luminance information
Bit 24:31 | Must be zero.
`V4L2_CID_MPEG_MFC51_VIDEO_RC_REACTION_COEFF` | integer
Reaction coefficient for MFC rate control. Applicable to encoders. Note 1: Valid only when the frame level RC is enabled. Note 2: For tight CBR, this field must be small (ex. 2 ~ 10). For VBR, this field must be large (ex. 100 ~ 1000). Note 3: It is not recommended to use the greater number than FRAME_RATE * (10^9 / BIT_RATE).
`V4L2_CID_MPEG_MFC51_VIDEO_H264_ADAPTIVE_RC_DARK` | boolean
Adaptive rate control for dark region. Valid only when H.264 and macroblock level RC is enabled (`V4L2_CID_MPEG_VIDEO_MB_RC_ENABLE`). Applicable to the H264 encoder.
`V4L2_CID_MPEG_MFC51_VIDEO_H264_ADAPTIVE_RC_SMOOTH` | boolean
Adaptive rate control for smooth region. Valid only when H.264 and macroblock level RC is enabled (`V4L2_CID_MPEG_VIDEO_MB_RC_ENABLE`). Applicable to the H264 encoder.
`V4L2_CID_MPEG_MFC51_VIDEO_H264_ADAPTIVE_RC_STATIC` | boolean
Adaptive rate control for static region. Valid only when H.264 and macroblock level RC is enabled (`V4L2_CID_MPEG_VIDEO_MB_RC_ENABLE`). Applicable to the H264 encoder.
`V4L2_CID_MPEG_MFC51_VIDEO_H264_ADAPTIVE_RC_ACTIVITY` | boolean
Adaptive rate control for activity region. Valid only when H.264 and macroblock level RC is enabled (`V4L2_CID_MPEG_VIDEO_MB_RC_ENABLE`). Applicable to the H264 encoder.
`V4L2_CID_MPEG_MFC51_VIDEO_FRAME_SKIP_MODE` | enum v4l2_mpeg_mfc51_video_frame_skip_mode
Indicates in what conditions the encoder should skip frames. If encoding a frame would cause the encoded stream to be larger then a chosen data limit then the frame will be skipped. Possible values are:
`V4L2_MPEG_MFC51_FRAME_SKIP_MODE_DISABLED` | Frame skip mode is disabled.
`V4L2_MPEG_MFC51_FRAME_SKIP_MODE_LEVEL_LIMIT` | Frame skip mode enabled and buffer limit is set by the chosen level and is defined by the standard.
`V4L2_MPEG_MFC51_FRAME_SKIP_MODE_BUF_LIMIT` | Frame skip mode enabled and buffer limit is set by the VBV (MPEG1/2/4) or CPB (H264) buffer size control.

V4L2_CID_MPEG_MFC51_VIDEO_RC_FIXED_TARGET_BIT
integer
Enable rate-control with fixed target bit. If this setting is enabled, then the rate control logic of the encoder will calculate the average bitrate for a GOP and keep it below or equal the set bitrate target. Otherwise the rate control logic calculates the overall average bitrate for the stream and keeps it below or equal to the set bitrate. In the first case the average bitrate for the whole stream will be smaller then the set bitrate. This is caused because the average is calculated for smaller number of frames, on the other hand enabling this setting will ensure that the stream will meet tight bandwidth contraints. Applicable to encoders.
V4L2_CID_MPEG_MFC51_VIDEO_FORCE_FRAME_TYPE
enum v4l2_mpeg_mfc51_video_force_frame_type
Force a frame type for the next queued buffer. Applicable to encoders. Possible values are:
V4L2_MPEG_MFC51_FORCE_FRAME_TYPE_DISABLED
Forcing a specific frame type disabled.
V4L2_MPEG_MFC51_FORCE_FRAME_TYPE_I_FRAME
Force an I-frame.
V4L2_MPEG_MFC51_FORCE_FRAME_TYPE_NOT_CODED
Force a non-coded frame.

### CX2341x MPEG Controls

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

#### CX2341x Control IDs

ID | Type
--- | ---
Description
`V4L2_CID_MPEG_CX2341X_VIDEO_SPATIAL_FILTER_MODE` | enum v4l2_mpeg_cx2341x_video_spatial_filter_mode
Sets the Spatial Filter mode (default `MANUAL`). Possible values are:
`V4L2_MPEG_CX2341X_VIDEO_SPATIAL_FILTER_MODE_MANUAL` | Choose the filter manually
`V4L2_MPEG_CX2341X_VIDEO_SPATIAL_FILTER_MODE_AUTO` | Choose the filter automatically
`V4L2_CID_MPEG_CX2341X_VIDEO_SPATIAL_FILTER` | integer (0-15)
The setting for the Spatial Filter. 0 = off, 15 = maximum. (Default is 0.)
`V4L2_CID_MPEG_CX2341X_VIDEO_LUMA_SPATIAL_FILTER_TYPE` | enum v4l2_mpeg_cx2341x_video_luma_spatial_filter_type
Select the algorithm to use for the Luma Spatial Filter (default `1D_HOR`). Possible values:
`V4L2_MPEG_CX2341X_VIDEO_LUMA_SPATIAL_FILTER_TYPE_OFF` | No filter
`V4L2_MPEG_CX2341X_VIDEO_LUMA_SPATIAL_FILTER_TYPE_1D_HOR` | One-dimensional horizontal
`V4L2_MPEG_CX2341X_VIDEO_LUMA_SPATIAL_FILTER_TYPE_1D_VERT` | One-dimensional vertical
`V4L2_MPEG_CX2341X_VIDEO_LUMA_SPATIAL_FILTER_TYPE_2D_HV_SEPARABLE` | Two-dimensional separable
`V4L2_MPEG_CX2341X_VIDEO_LUMA_SPATIAL_FILTER_TYPE_2D_SYM_NON_SEPARABLE` | Two-dimensional symmetrical non-separable

V4L2_CID_MPEG_CX2341X_VIDEO_CHROMA_SPATIAL_FILTER_TYPE
enum v4l2_mpeg_cx2341x_video_chroma_spatial_filter_type
Select the algorithm for the Chroma Spatial Filter (default `1D_HOR`). Possible values are:
V4L2_MPEG_CX2341X_VIDEO_CHROMA_SPATIAL_FILTER_TYPE_OFF
No filter
V4L2_MPEG_CX2341X_VIDEO_CHROMA_SPATIAL_FILTER_TYPE_1D_HOR
One-dimensional horizontal
V4L2_CID_MPEG_CX2341X_VIDEO_TEMPORAL_FILTER_MODE
enum v4l2_mpeg_cx2341x_video_temporal_filter_mode
Sets the Temporal Filter mode (default `MANUAL`). Possible values are:
V4L2_MPEG_CX2341X_VIDEO_TEMPORAL_FILTER_MODE_MANUAL
Choose the filter manually
V4L2_MPEG_CX2341X_VIDEO_TEMPORAL_FILTER_MODE_AUTO
Choose the filter automatically
V4L2_CID_MPEG_CX2341X_VIDEO_TEMPORAL_FILTER
integer (0-31)
The setting for the Temporal Filter. 0 = off, 31 = maximum. (Default is 8 for full-scale capturing and 0 for scaled capturing.)
V4L2_CID_MPEG_CX2341X_VIDEO_MEDIAN_FILTER_TYPE
enum v4l2_mpeg_cx2341x_video_median_filter_type
Median Filter Type (default `OFF`). Possible values are:
V4L2_MPEG_CX2341X_VIDEO_MEDIAN_FILTER_TYPE_OFF
No filter
V4L2_MPEG_CX2341X_VIDEO_MEDIAN_FILTER_TYPE_HOR
Horizontal filter
V4L2_MPEG_CX2341X_VIDEO_MEDIAN_FILTER_TYPE_VERT
Vertical filter
V4L2_MPEG_CX2341X_VIDEO_MEDIAN_FILTER_TYPE_HOR_VERT
Horizontal and vertical filter
V4L2_MPEG_CX2341X_VIDEO_MEDIAN_FILTER_TYPE_DIAG
Diagonal filter
V4L2_CID_MPEG_CX2341X_VIDEO_LUMA_MEDIAN_FILTER_BOTTOM
integer (0-255)
Threshold above which the luminance median filter is enabled (default 0)
V4L2_CID_MPEG_CX2341X_VIDEO_LUMA_MEDIAN_FILTER_TOP
integer (0-255)
Threshold below which the luminance median filter is enabled (default 255)
V4L2_CID_MPEG_CX2341X_VIDEO_CHROMA_MEDIAN_FILTER_BOTTOM
integer (0-255)
Threshold above which the chroma median filter is enabled (default 0)
V4L2_CID_MPEG_CX2341X_VIDEO_CHROMA_MEDIAN_FILTER_TOP
integer (0-255)
Threshold below which the chroma median filter is enabled (default 255)
V4L2_CID_MPEG_CX2341X_STREAM_INSERT_NAV_PACKETS
boolean
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.

## Camera Control Reference

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

### Camera Control IDs

ID | Type
--- | ---
Description
`V4L2_CID_CAMERA_CLASS` | class
The Camera class descriptor. Calling &VIDIOC-QUERYCTRL; for this control will return a description of this control class.
`V4L2_CID_EXPOSURE_AUTO` | enum v4l2_exposure_auto_type
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:
`V4L2_EXPOSURE_AUTO` | Automatic exposure time, automatic iris aperture.
`V4L2_EXPOSURE_MANUAL` | Manual exposure time, manual iris.
`V4L2_EXPOSURE_SHUTTER_PRIORITY` | Manual exposure time, auto iris.
`V4L2_EXPOSURE_APERTURE_PRIORITY` | Auto exposure time, manual iris.
`V4L2_CID_EXPOSURE_ABSOLUTE` | integer
Determines the exposure time of the camera sensor. The exposure time is limited by the frame interval. Drivers should interpret the values as 100 µs units, where the value 1 stands for 1/10000th of a second, 10000 for 1 second and 100000 for 10 seconds.
`V4L2_CID_EXPOSURE_AUTO_PRIORITY` | boolean
When `V4L2_CID_EXPOSURE_AUTO` is set to `AUTO` or `APERTURE_PRIORITY`, 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.
`V4L2_CID_PAN_RELATIVE` | integer
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.
`V4L2_CID_TILT_RELATIVE` | integer
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.
`V4L2_CID_PAN_RESET` | button
When this control is set, the camera moves horizontally to the default position.
`V4L2_CID_TILT_RESET` | button
When this control is set, the camera moves vertically to the default position.
`V4L2_CID_PAN_ABSOLUTE` | integer
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.
`V4L2_CID_TILT_ABSOLUTE` | integer
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.
`V4L2_CID_FOCUS_ABSOLUTE` | integer
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.
`V4L2_CID_FOCUS_RELATIVE` | integer
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.
`V4L2_CID_FOCUS_AUTO` | boolean
Enables automatic focus adjustments. The effect of manual focus adjustments while this feature is enabled is undefined, drivers should ignore such requests.
`V4L2_CID_ZOOM_ABSOLUTE` | integer
Specify the objective lens focal length as an absolute value. The zoom unit is driver-specific and its value should be a positive integer.
`V4L2_CID_ZOOM_RELATIVE` | integer
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.
`V4L2_CID_ZOOM_CONTINUOUS` | integer
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.
`V4L2_CID_IRIS_ABSOLUTE` | integer
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.
`V4L2_CID_IRIS_RELATIVE` | integer
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.
`V4L2_CID_PRIVACY` | boolean
Prevent video from being acquired by the camera. When this control is set to `TRUE` (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.
`V4L2_CID_BAND_STOP_FILTER` | integer
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.

## FM Transmitter Control Reference

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.

### FM_TX Control IDs

ID | Type
--- | ---
Description
`V4L2_CID_FM_TX_CLASS` | class
The FM_TX class descriptor. Calling &VIDIOC-QUERYCTRL; for this control will return a description of this control class.
`V4L2_CID_RDS_TX_DEVIATION` | integer
Configures RDS signal frequency deviation level in Hz. The range and step are driver-specific.
`V4L2_CID_RDS_TX_PI` | integer
Sets the RDS Programme Identification field for transmission.
`V4L2_CID_RDS_TX_PTY` | integer
Sets the RDS Programme Type field for transmission. This encodes up to 31 pre-defined programme types.
`V4L2_CID_RDS_TX_PS_NAME` | string

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 , 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.

`V4L2_CID_RDS_TX_RADIO_TEXT` | string

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 `V4L2_CID_RDS_TX_PS_NAME`. The encoding for Radio Text strings is also fully described in Annex E of . 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.

`V4L2_CID_AUDIO_LIMITER_ENABLED` | boolean
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.
`V4L2_CID_AUDIO_LIMITER_RELEASE_TIME` | integer
Sets the audio deviation limiter feature release time. Unit is in useconds. Step and range are driver-specific.
`V4L2_CID_AUDIO_LIMITER_DEVIATION` | integer
Configures audio frequency deviation level in Hz. The range and step are driver-specific.
`V4L2_CID_AUDIO_COMPRESSION_ENABLED` | boolean
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).
`V4L2_CID_AUDIO_COMPRESSION_GAIN` | integer
Sets the gain for audio compression feature. It is a dB value. The range and step are driver-specific.
`V4L2_CID_AUDIO_COMPRESSION_THRESHOLD` | integer
Sets the threshold level for audio compression freature. It is a dB value. The range and step are driver-specific.
`V4L2_CID_AUDIO_COMPRESSION_ATTACK_TIME` | integer
Sets the attack time for audio compression feature. It is a useconds value. The range and step are driver-specific.
`V4L2_CID_AUDIO_COMPRESSION_RELEASE_TIME` | integer
Sets the release time for audio compression feature. It is a useconds value. The range and step are driver-specific.
`V4L2_CID_PILOT_TONE_ENABLED` | boolean
Enables or disables the pilot tone generation feature.
`V4L2_CID_PILOT_TONE_DEVIATION` | integer
Configures pilot tone frequency deviation level. Unit is in Hz. The range and step are driver-specific.
`V4L2_CID_PILOT_TONE_FREQUENCY` | integer
Configures pilot tone frequency value. Unit is in Hz. The range and step are driver-specific.
`V4L2_CID_TUNE_PREEMPHASIS` | integer
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 v4l2_preemphasis defines possible values for pre-emphasis. Here they are:
`V4L2_PREEMPHASIS_DISABLED` | No pre-emphasis is applied.
`V4L2_PREEMPHASIS_50_uS` | A pre-emphasis of 50 uS is used.
`V4L2_PREEMPHASIS_75_uS` | A pre-emphasis of 75 uS is used.
`V4L2_CID_TUNE_POWER_LEVEL` | integer
Sets the output power level for signal transmission. Unit is in dBuV. Range and step are driver-specific.
`V4L2_CID_TUNE_ANTENNA_CAPACITOR` | integer
This selects the value of antenna tuning capacitor manually or automatically if set to zero. Unit, range and step are driver-specific.

For more details about RDS specification, refer to document, from CENELEC.

## Flash Control Reference

### Experimental

This is an experimental interface and may change in the future.

The V4L2 flash controls are intended to provide generic access to flash controller devices. Flash controller devices are typically used in digital cameras.

The interface can support both LED and xenon flash devices. As of writing this, there is no xenon flash driver using this interface.

### Supported use cases

#### Unsynchronised LED flash (software strobe)

Unsynchronised LED flash is controlled directly by the host as the sensor. The flash must be enabled by the host before the exposure of the image starts and disabled once it ends. The host is fully responsible for the timing of the flash.

Example of such device: Nokia N900.

#### Synchronised LED flash (hardware strobe)

The synchronised LED flash is pre-programmed by the host (power and timeout) but controlled by the sensor through a strobe signal from the sensor to the flash.

The sensor controls the flash duration and timing. This information typically must be made available to the sensor.

#### LED flash as torch

LED flash may be used as torch in conjunction with another use case involving camera or individually.

### Flash Control IDs

ID | Type
--- | ---
Description
`V4L2_CID_FLASH_CLASS` | class
The FLASH class descriptor.
`V4L2_CID_FLASH_LED_MODE` | menu
Defines the mode of the flash LED, the high-power white LED attached to the flash controller. Setting this control may not be possible in presence of some faults. See V4L2_CID_FLASH_FAULT.
`V4L2_FLASH_LED_MODE_NONE` | Off.
`V4L2_FLASH_LED_MODE_FLASH` | Flash mode.
`V4L2_FLASH_LED_MODE_TORCH` | Torch mode. See V4L2_CID_FLASH_TORCH_INTENSITY.
`V4L2_CID_FLASH_STROBE_SOURCE` | menu
Defines the source of the flash LED strobe.
`V4L2_FLASH_STROBE_SOURCE_SOFTWARE` | The flash strobe is triggered by using the V4L2_CID_FLASH_STROBE control.
`V4L2_FLASH_STROBE_SOURCE_EXTERNAL` | The flash strobe is triggered by an external source. Typically this is a sensor, which makes it possible to synchronises the flash strobe start to exposure start.

V4L2_CID_FLASH_STROBE
button
Strobe flash. Valid when V4L2_CID_FLASH_LED_MODE is set to V4L2_FLASH_LED_MODE_FLASH and V4L2_CID_FLASH_STROBE_SOURCE is set to V4L2_FLASH_STROBE_SOURCE_SOFTWARE. Setting this control may not be possible in presence of some faults. See V4L2_CID_FLASH_FAULT.
V4L2_CID_FLASH_STROBE_STOP
button
Stop flash strobe immediately.
V4L2_CID_FLASH_STROBE_STATUS
boolean
Strobe status: whether the flash is strobing at the moment or not. This is a read-only control.
V4L2_CID_FLASH_TIMEOUT
integer
Hardware timeout for flash. The flash strobe is stopped after this period of time has passed from the start of the strobe.
V4L2_CID_FLASH_INTENSITY
integer
Intensity of the flash strobe when the flash LED is in flash mode (V4L2_FLASH_LED_MODE_FLASH). The unit should be milliamps (mA) if possible.
V4L2_CID_FLASH_TORCH_INTENSITY
integer
Intensity of the flash LED in torch mode (V4L2_FLASH_LED_MODE_TORCH). The unit should be milliamps (mA) if possible. Setting this control may not be possible in presence of some faults. See V4L2_CID_FLASH_FAULT.
V4L2_CID_FLASH_INDICATOR_INTENSITY
integer
Intensity of the indicator LED. The indicator LED may be fully independent of the flash LED. The unit should be microamps (uA) if possible.
V4L2_CID_FLASH_FAULT
bitmask
Faults related to the flash. The faults tell about specific problems in the flash chip itself or the LEDs attached to it. Faults may prevent further use of some of the flash controls. In particular, V4L2_CID_FLASH_LED_MODE is set to V4L2_FLASH_LED_MODE_NONE if the fault affects the flash LED. Exactly which faults have such an effect is chip dependent. Reading the faults resets the control and returns the chip to a usable state if possible.
V4L2_FLASH_FAULT_OVER_VOLTAGE
Flash controller voltage to the flash LED has exceeded the limit specific to the flash controller.
V4L2_FLASH_FAULT_TIMEOUT
The flash strobe was still on when the timeout set by the user --- V4L2_CID_FLASH_TIMEOUT control --- has expired. Not all flash controllers may set this in all such conditions.
V4L2_FLASH_FAULT_OVER_TEMPERATURE
The flash controller has overheated.
V4L2_FLASH_FAULT_SHORT_CIRCUIT
The short circuit protection of the flash controller has been triggered.
V4L2_FLASH_FAULT_OVER_CURRENT
Current in the LED power supply has exceeded the limit specific to the flash controller.
V4L2_FLASH_FAULT_INDICATOR
The flash controller has detected a short or open circuit condition on the indicator LED.
V4L2_CID_FLASH_CHARGE
boolean
Enable or disable charging of the xenon flash capacitor.
V4L2_CID_FLASH_READY
boolean
Is the flash ready to strobe? Xenon flashes require their capacitors charged before strobing. LED flashes often require a cooldown period after strobe during which another strobe will not be possible. This is a read-only control.

## JPEG Control Reference

The JPEG class includes controls for common features of JPEG encoders and decoders. Currently it includes features for codecs implementing progressive baseline DCT compression process with Huffman entrophy coding.

### JPEG Control IDs

ID | Type
--- | ---
Description
`V4L2_CID_JPEG_CLASS` | class
The JPEG class descriptor. Calling &VIDIOC-QUERYCTRL; for this control will return a description of this control class.
`V4L2_CID_JPEG_CHROMA_SUBSAMPLING` | menu
The chroma subsampling factors describe how each component of an input image is sampled, in respect to maximum sample rate in each spatial dimension. See , clause A.1.1. for more details. The `V4L2_CID_JPEG_CHROMA_SUBSAMPLING` control determines how Cb and Cr components are downsampled after coverting an input image from RGB to Y'CbCr color space.
`V4L2_JPEG_CHROMA_SUBSAMPLING_444` | No chroma subsampling, each pixel has Y, Cr and Cb values.
`V4L2_JPEG_CHROMA_SUBSAMPLING_422` | Horizontally subsample Cr, Cb components by a factor of 2.
`V4L2_JPEG_CHROMA_SUBSAMPLING_420` | Subsample Cr, Cb components horizontally and vertically by 2.
`V4L2_JPEG_CHROMA_SUBSAMPLING_411` | Horizontally subsample Cr, Cb components by a factor of 4.
`V4L2_JPEG_CHROMA_SUBSAMPLING_410` | Subsample Cr, Cb components horizontally by 4 and vertically by 2.
`V4L2_JPEG_CHROMA_SUBSAMPLING_GRAY` | Use only luminance component.
`V4L2_CID_JPEG_RESTART_INTERVAL` | integer

The restart interval determines an interval of inserting RSTm markers (m = 0..7). The purpose of these markers is to additionally reinitialize the encoder process, in order to process blocks of an image independently. For the lossy compression processes the restart interval unit is MCU (Minimum Coded Unit) and its value is contained in DRI (Define Restart Interval) marker. If `V4L2_CID_JPEG_RESTART_INTERVAL` control is set to 0, DRI and RSTm markers will not be inserted.

`V4L2_CID_JPEG_COMPRESION_QUALITY` | integer

`V4L2_CID_JPEG_COMPRESION_QUALITY` control determines trade-off between image quality and size. It provides simpler method for applications to control image quality, without a need for direct reconfiguration of luminance and chrominance quantization tables. In cases where a driver uses quantization tables configured directly by an application, using interfaces defined elsewhere, `V4L2_CID_JPEG_COMPRESION_QUALITY` control should be set by driver to 0.

The value range of this control is driver-specific. Only positive, non-zero values are meaningful. The recommended range is 1 - 100, where larger values correspond to better image quality.

`V4L2_CID_JPEG_ACTIVE_MARKER` | bitmask
Specify which JPEG markers are included in compressed stream. This control is valid only for encoders.
`V4L2_JPEG_ACTIVE_MARKER_APP0` | Application data segment APP0.
`V4L2_JPEG_ACTIVE_MARKER_APP1` | Application data segment APP1.
`V4L2_JPEG_ACTIVE_MARKER_COM` | Comment segment.
`V4L2_JPEG_ACTIVE_MARKER_DQT` | Quantization tables segment.
`V4L2_JPEG_ACTIVE_MARKER_DHT` | Huffman tables segment.

For more details about JPEG specification, refer to , , .