Video for Linux Two API Specification: Revision 0.24
Prev | Chapter 1. Common API Elements | Next

# 1.9. Extended Controls

## 1.9.1. 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.

## 1.9.2. 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 struct 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 (i. e. 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 struct v4l2_ext_control array. The `v4l2_ext_control` structure is very similar to struct v4l2_control, except for the fact that it also allows for 64-bit values and pointers to be passed (although the latter is not yet used anywhere).

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.

## 1.9.3. 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:

    struct 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 (e. g. `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.

## 1.9.4. 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 struct v4l2_queryctrl also contains hints on the behavior of the control. See the `VIDIOC_QUERYCTRL` documentation for more details.

## 1.9.5. MPEG Control Reference

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

### 1.9.5.1. Generic MPEG Controls

Table 1-2. 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 |
| The MPEG-1, -2 or -4 output stream type. One cannot assume anything here. Each hardware MPEG encoder tends to support different subsets of the available MPEG stream types. The currently defined stream types are:

`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 |
| Some cards can embed VBI data (e. g. 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 |
| 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 |
| MPEG Audio encoding. Possible values are:

`V4L2_MPEG_AUDIO_ENCODING_LAYER_1` | MPEG Layer I encoding
`V4L2_MPEG_AUDIO_ENCODING_LAYER_2` | MPEG Layer II encoding
`V4L2_MPEG_AUDIO_ENCODING_LAYER_3` | MPEG Layer III encoding

`V4L2_CID_MPEG_AUDIO_L1_BITRATE` | enum |
| 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 |
| 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 |
| 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_MODE` | enum |
| 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 |
| 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 |
| 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 |
| 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` | bool |
| Mutes the audio when capturing. This is not done by muting audio hardware, which can still produce a slight hiss, but in the encoder itself, guaranteeing a fixed and reproducable audio bitstream. 0 = unmuted, 1 = muted.
`V4L2_CID_MPEG_VIDEO_ENCODING` | enum |
| MPEG Video encoding method. Possible values are:

`V4L2_MPEG_VIDEO_ENCODING_MPEG_1` | MPEG-1 Video encoding
`V4L2_MPEG_VIDEO_ENCODING_MPEG_2` | MPEG-2 Video encoding

`V4L2_CID_MPEG_VIDEO_ASPECT` | enum |
| 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` | bool |
| GOP closure (default 1)
`V4L2_CID_MPEG_VIDEO_PULLDOWN` | bool |
| Enable 3:2 pulldown (default 0)
`V4L2_CID_MPEG_VIDEO_BITRATE_MODE` | enum |
| 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` | bool |
| "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.

### 1.9.5.2. 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.

Table 1-3. CX2341x Control IDs

ID | Type |
| Description
--- | ---
`V4L2_CID_MPEG_CX2341X_VIDEO_SPATIAL_FILTER_MODE` | enum |
| 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 |
| 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 |
| 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 |
| 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 |
| 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` | bool |
| 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.

## 1.9.6. Camera Control Reference

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

Table 1-4. 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` | integer |
| 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 `SHUTTER_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.
`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.
`V4L2_CID_PAN_RESET` | boolean |
| When this control is set to `TRUE` (1), the camera moves horizontally to the default position.
`V4L2_CID_TILT_RESET` | boolean |
| When this control is set to `TRUE` (1), 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.
`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.

Prev | Home | Next
User Controls | Up | Data Formats