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.
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.
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.
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.
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.
Below all controls within the MPEG control class are described. First the generic controls, then controls specific for certain hardware.
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 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. The currently defined stream types are: | |||||||||||||||||||||||||||||||||||||||||
| |||||||||||||||||||||||||||||||||||||||||
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 (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_CID_MPEG_AUDIO_SAMPLING_FREQ | enum v4l2_mpeg_audio_sampling_freq | ||||||||||||||||||||||||||||||||||||||||
MPEG Audio sampling frequency. Possible values are: | |||||||||||||||||||||||||||||||||||||||||
| |||||||||||||||||||||||||||||||||||||||||
V4L2_CID_MPEG_AUDIO_ENCODING | enum v4l2_mpeg_audio_encoding | ||||||||||||||||||||||||||||||||||||||||
MPEG Audio encoding. Possible values are: | |||||||||||||||||||||||||||||||||||||||||
| |||||||||||||||||||||||||||||||||||||||||
V4L2_CID_MPEG_AUDIO_L1_BITRATE | enum v4l2_mpeg_audio_l1_bitrate | ||||||||||||||||||||||||||||||||||||||||
MPEG-1/2 Layer I bitrate. Possible values are: | |||||||||||||||||||||||||||||||||||||||||
| |||||||||||||||||||||||||||||||||||||||||
V4L2_CID_MPEG_AUDIO_L2_BITRATE | enum v4l2_mpeg_audio_l2_bitrate | ||||||||||||||||||||||||||||||||||||||||
MPEG-1/2 Layer II bitrate. Possible values are: | |||||||||||||||||||||||||||||||||||||||||
| |||||||||||||||||||||||||||||||||||||||||
V4L2_CID_MPEG_AUDIO_L3_BITRATE | enum v4l2_mpeg_audio_l3_bitrate | ||||||||||||||||||||||||||||||||||||||||
MPEG-1/2 Layer III bitrate. Possible values are: | |||||||||||||||||||||||||||||||||||||||||
| |||||||||||||||||||||||||||||||||||||||||
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_CID_MPEG_AUDIO_MODE | enum v4l2_mpeg_audio_mode | ||||||||||||||||||||||||||||||||||||||||
MPEG Audio mode. Possible values are: | |||||||||||||||||||||||||||||||||||||||||
| |||||||||||||||||||||||||||||||||||||||||
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_CID_MPEG_AUDIO_EMPHASIS | enum v4l2_mpeg_audio_emphasis | ||||||||||||||||||||||||||||||||||||||||
Audio Emphasis. Possible values are: | |||||||||||||||||||||||||||||||||||||||||
| |||||||||||||||||||||||||||||||||||||||||
V4L2_CID_MPEG_AUDIO_CRC | enum v4l2_mpeg_audio_crc | ||||||||||||||||||||||||||||||||||||||||
CRC method. Possible values are: | |||||||||||||||||||||||||||||||||||||||||
| |||||||||||||||||||||||||||||||||||||||||
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 reproducable audio bitstream. 0 = unmuted, 1 = muted. | |||||||||||||||||||||||||||||||||||||||||
V4L2_CID_MPEG_VIDEO_ENCODING | enum v4l2_mpeg_video_encoding | ||||||||||||||||||||||||||||||||||||||||
MPEG Video encoding method. Possible values are: | |||||||||||||||||||||||||||||||||||||||||
| |||||||||||||||||||||||||||||||||||||||||
V4L2_CID_MPEG_VIDEO_ASPECT | enum v4l2_mpeg_video_aspect | ||||||||||||||||||||||||||||||||||||||||
Video aspect. Possible values are: | |||||||||||||||||||||||||||||||||||||||||
| |||||||||||||||||||||||||||||||||||||||||
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_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): | |||||||||||||||||||||||||||||||||||||||||
|
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
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 | 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_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_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. | |||||||||||
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.
Table 1.5. 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 [EN 50067], 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 [EN 50067]. 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_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 [EN 50067] document, from CENELEC.