time.
Since these features cannot be implemented entirely in user space V4L2
-defines the :ref:`VIDIOC_G_PRIORITY` and
+defines the :ref:`VIDIOC_G_PRIORITY <VIDIOC_G_PRIORITY>` and
:ref:`VIDIOC_S_PRIORITY <VIDIOC_G_PRIORITY>` ioctls to request and
query the access priority associate with a file descriptor. Opening a
device assigns a medium priority, compatible with earlier versions of
:ref:`VIDIOC_ENUMAUDIO` ioctl also contains signal
:status information applicable when the current audio input is queried.
-The :ref:`VIDIOC_G_AUDIO` and
+The :ref:`VIDIOC_G_AUDIO <VIDIOC_G_AUDIO>` and
:ref:`VIDIOC_G_AUDOUT <VIDIOC_G_AUDIOout>` ioctls report the current
audio input and output, respectively. Note that, unlike
-:ref:`VIDIOC_G_INPUT` and
-:ref:`VIDIOC_G_OUTPUT` these ioctls return a
+:ref:`VIDIOC_G_INPUT <VIDIOC_G_INPUT>` and
+:ref:`VIDIOC_G_OUTPUT <VIDIOC_G_OUTPUT>` these ioctls return a
structure as :ref:`VIDIOC_ENUMAUDIO` and
:ref:`VIDIOC_ENUMAUDOUT <VIDIOC_ENUMAUDIOout>` do, not just an index.
Applications can enumerate the available controls with the
:ref:`VIDIOC_QUERYCTRL` and
:ref:`VIDIOC_QUERYMENU <VIDIOC_QUERYCTRL>` ioctls, get and set a
-control value with the :ref:`VIDIOC_G_CTRL` and
+control value with the :ref:`VIDIOC_G_CTRL <VIDIOC_G_CTRL>` and
:ref:`VIDIOC_S_CTRL <VIDIOC_G_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
Applications can use the following API to select an area in the video
signal, query the default area and the hardware limits. *Despite their
name, the :ref:`VIDIOC_CROPCAP`,
-:ref:`VIDIOC_G_CROP` and
+:ref:`VIDIOC_G_CROP <VIDIOC_G_CROP>` and
:ref:`VIDIOC_S_CROP <VIDIOC_G_CROP>` ioctls apply to input as well
as output devices.*
device the source is the video signal, and the cropping ioctls determine
the area actually sampled. The target are images read by the application
or overlaid onto the graphics screen. Their size (and position for an
-overlay) is negotiated with the :ref:`VIDIOC_G_FMT`
+overlay) is negotiated with the :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>`
and :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctls.
On a video output device the source are the images passed in by the
a struct :ref:`v4l2_format <v4l2-format>` to
``V4L2_BUF_TYPE_VIDEO_CAPTURE`` or
``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE`` and call the
-:ref:`VIDIOC_G_FMT` ioctl with a pointer to this
+:ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` ioctl with a pointer to this
structure. Drivers fill the struct
:ref:`v4l2_pix_format <v4l2-pix-format>` ``pix`` or the struct
:ref:`v4l2_pix_format_mplane <v4l2-pix-format-mplane>` ``pix_mp``
struct :ref:`v4l2_format <v4l2-format>` as above and initialize all
fields of the struct :ref:`v4l2_pix_format <v4l2-pix-format>`
``vbi`` member of the ``fmt`` union, or better just modify the results
-of :ref:`VIDIOC_G_FMT`, and call the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>`
+of :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>`, and call the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>`
ioctl with a pointer to this structure. Drivers may adjust the
-parameters and finally return the actual parameters as :ref:`VIDIOC_G_FMT`
+parameters and finally return the actual parameters as :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>`
does.
Like :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` the :ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>` ioctl
The contents of struct :ref:`v4l2_pix_format <v4l2-pix-format>` and
struct :ref:`v4l2_pix_format_mplane <v4l2-pix-format-mplane>` are
discussed in :ref:`pixfmt`. See also the specification of the
-:ref:`VIDIOC_G_FMT`, :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` and :ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>` ioctls for
-details. Video capture devices must implement both the :ref:`VIDIOC_G_FMT`
+:ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>`, :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` and :ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>` ioctls for
+details. Video capture devices must implement both the :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>`
and :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl, even if :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ignores all
-requests and always returns default parameters as :ref:`VIDIOC_G_FMT` does.
+requests and always returns default parameters as :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` does.
:ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>` is optional.
implemented on the TV card and not the graphics card. On Linux it is
accessible as a framebuffer device (``/dev/fbN``). Given a V4L2 device,
applications can find the corresponding framebuffer device by calling
-the :ref:`VIDIOC_G_FBUF` ioctl. It returns, amongst
+the :ref:`VIDIOC_G_FBUF <VIDIOC_G_FBUF>` ioctl. It returns, amongst
other information, the physical address of the framebuffer in the
``base`` field of struct :ref:`v4l2_framebuffer <v4l2-framebuffer>`.
The framebuffer device ioctl ``FBIOGET_FSCREENINFO`` returns the same
parameters applications set the ``type`` field of a struct
:ref:`v4l2_format <v4l2-format>` to
``V4L2_BUF_TYPE_VIDEO_OUTPUT_OVERLAY`` and call the
-:ref:`VIDIOC_G_FMT` ioctl. The driver fills the
+:ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` ioctl. The driver fills the
:c:type:`struct v4l2_window` substructure named ``win``. It is not
possible to retrieve a previously programmed clipping list or bitmap.
``V4L2_BUF_TYPE_VIDEO_OUTPUT_OVERLAY``, initialize the ``win``
substructure and call the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl.
The driver adjusts the parameters against hardware limits and returns
-the actual parameters as :ref:`VIDIOC_G_FMT` does. Like :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>`,
+the actual parameters as :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` does. Like :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>`,
the :ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>` ioctl can be used to learn
about driver capabilities without actually changing driver state. Unlike
:ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` this also works after the overlay has been enabled.
To query the current image format applications set the ``type`` field of
a struct :ref:`v4l2_format <v4l2-format>` to
``V4L2_BUF_TYPE_VIDEO_OUTPUT`` or ``V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE``
-and call the :ref:`VIDIOC_G_FMT` ioctl with a pointer
+and call the :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` ioctl with a pointer
to this structure. Drivers fill the struct
:ref:`v4l2_pix_format <v4l2-pix-format>` ``pix`` or the struct
:ref:`v4l2_pix_format_mplane <v4l2-pix-format-mplane>` ``pix_mp``
struct :ref:`v4l2_format <v4l2-format>` as above and initialize all
fields of the struct :ref:`v4l2_pix_format <v4l2-pix-format>`
``vbi`` member of the ``fmt`` union, or better just modify the results
-of :ref:`VIDIOC_G_FMT`, and call the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>`
+of :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>`, and call the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>`
ioctl with a pointer to this structure. Drivers may adjust the
-parameters and finally return the actual parameters as :ref:`VIDIOC_G_FMT`
+parameters and finally return the actual parameters as :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>`
does.
Like :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` the :ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>` ioctl
The contents of struct :ref:`v4l2_pix_format <v4l2-pix-format>` and
struct :ref:`v4l2_pix_format_mplane <v4l2-pix-format-mplane>` are
discussed in :ref:`pixfmt`. See also the specification of the
-:ref:`VIDIOC_G_FMT`, :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` and :ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>` ioctls for
-details. Video output devices must implement both the :ref:`VIDIOC_G_FMT`
+:ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>`, :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` and :ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>` ioctls for
+details. Video output devices must implement both the :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>`
and :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl, even if :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ignores all
-requests and always returns default parameters as :ref:`VIDIOC_G_FMT` does.
+requests and always returns default parameters as :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` does.
:ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>` is optional.
Before overlay can commence applications must program the driver with
frame buffer parameters, namely the address and size of the frame buffer
and the image format, for example RGB 5:6:5. The
-:ref:`VIDIOC_G_FBUF` and
+:ref:`VIDIOC_G_FBUF <VIDIOC_G_FBUF>` and
:ref:`VIDIOC_S_FBUF <VIDIOC_G_FBUF>` ioctls are available to get and
set these parameters, respectively. The :ref:`VIDIOC_S_FBUF <VIDIOC_G_FBUF>` ioctl is
privileged because it allows to set up DMA into physical memory,
card. In this case the frame buffer is not modified by the video device,
and the frame buffer address and pixel format are not needed by the
driver. The :ref:`VIDIOC_S_FBUF <VIDIOC_G_FBUF>` ioctl is not privileged. An application
-can check for this type of device by calling the :ref:`VIDIOC_G_FBUF`
+can check for this type of device by calling the :ref:`VIDIOC_G_FBUF <VIDIOC_G_FBUF>`
ioctl.
A driver may support any (or none) of five clipping/blending methods:
To get the current parameters applications set the ``type`` field of a
struct :ref:`v4l2_format <v4l2-format>` to
``V4L2_BUF_TYPE_VIDEO_OVERLAY`` and call the
-:ref:`VIDIOC_G_FMT` ioctl. The driver fills the
+:ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` ioctl. The driver fills the
:c:type:`struct v4l2_window` substructure named ``win``. It is not
possible to retrieve a previously programmed clipping list or bitmap.
``V4L2_BUF_TYPE_VIDEO_OVERLAY``, initialize the ``win`` substructure and
call the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl. The driver
adjusts the parameters against hardware limits and returns the actual
-parameters as :ref:`VIDIOC_G_FMT` does. Like :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>`, the
+parameters as :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` does. Like :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>`, the
:ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>` ioctl can be used to learn
about driver capabilities without actually changing driver state. Unlike
:ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` this also works after the overlay has been enabled.
``struct v4l2_clip * clips``
When chroma-keying has *not* been negotiated and
- :ref:`VIDIOC_G_FBUF` indicated this capability,
+ :ref:`VIDIOC_G_FBUF <VIDIOC_G_FBUF>` indicated this capability,
applications can set this field to point to an array of clipping
rectangles.
``void * bitmap``
When chroma-keying has *not* been negotiated and
- :ref:`VIDIOC_G_FBUF` indicated this capability,
+ :ref:`VIDIOC_G_FBUF <VIDIOC_G_FBUF>` indicated this capability,
applications can set this field to point to a clipping bit mask.
It must be of the same size as the window, ``w.width`` and ``w.height``.
frequency and to determine if a monaural or FM stereo program is
received/emitted. Drivers switch automatically between AM and FM
depending on the selected frequency. The
-:ref:`VIDIOC_G_TUNER` or
-:ref:`VIDIOC_G_MODULATOR` ioctl reports the
+:ref:`VIDIOC_G_TUNER <VIDIOC_G_TUNER>` or
+:ref:`VIDIOC_G_MODULATOR <VIDIOC_G_MODULATOR>` ioctl reports the
supported frequency range.
To query the current raw VBI capture parameters applications set the
``type`` field of a struct :ref:`v4l2_format <v4l2-format>` to
``V4L2_BUF_TYPE_VBI_CAPTURE`` or ``V4L2_BUF_TYPE_VBI_OUTPUT``, and call
-the :ref:`VIDIOC_G_FMT` ioctl with a pointer to this
+the :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` ioctl with a pointer to this
structure. Drivers fill the struct
:ref:`v4l2_vbi_format <v4l2-vbi-format>` ``vbi`` member of the
``fmt`` union.
struct :ref:`v4l2_format <v4l2-format>` as above and initialize all
fields of the struct :ref:`v4l2_vbi_format <v4l2-vbi-format>`
``vbi`` member of the ``fmt`` union, or better just modify the results
-of :ref:`VIDIOC_G_FMT`, and call the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>`
+of :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>`, and call the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>`
ioctl with a pointer to this structure. Drivers return an EINVAL error
code only when the given parameters are ambiguous, otherwise they modify
the parameters according to the hardware capabilities and return the
:ref:`VIDIOC_STREAMON` ioctl and the first read(),
write() and select() call.
-VBI devices must implement both the :ref:`VIDIOC_G_FMT` and
+VBI devices must implement both the :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` and
:ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl, even if :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ignores all requests
-and always returns default parameters as :ref:`VIDIOC_G_FMT` does.
+and always returns default parameters as :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` does.
:ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>` is optional.
To find out which data services are supported by the hardware
applications can call the
-:ref:`VIDIOC_G_SLICED_VBI_CAP` ioctl.
+:ref:`VIDIOC_G_SLICED_VBI_CAP <VIDIOC_G_SLICED_VBI_CAP>` ioctl.
All drivers implementing the sliced VBI interface must support this
ioctl. The results may differ from those of the
:ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl when the number of VBI
``type`` field of struct :ref:`v4l2_format <v4l2-format>` to
``V4L2_BUF_TYPE_SLICED_VBI_CAPTURE`` or
``V4L2_BUF_TYPE_SLICED_VBI_OUTPUT``, and the
-:ref:`VIDIOC_G_FMT` ioctl fills the ``fmt.sliced``
+:ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` ioctl fills the ``fmt.sliced``
member, a struct
:ref:`v4l2_sliced_vbi_format <v4l2-sliced-vbi-format>`.
error code when applications violate this rule. They must also return an
EINVAL error code when applications pass an incorrect field or line
number, or a combination of ``field``, ``line`` and ``id`` which has not
-been negotiated with the :ref:`VIDIOC_G_FMT` or
+been negotiated with the :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` or
:ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl. When the line numbers are
unknown the driver must pass the packets in transmitted order. The
driver can insert empty packets with ``id`` set to zero anywhere in the
- ``-``
- - Applications can call the :ref:`VIDIOC_G_CROP`
+ - Applications can call the :ref:`VIDIOC_G_CROP <VIDIOC_G_CROP>`
ioctl to determine if the device supports capturing a subsection
of the full picture ("cropping" in V4L2). If not, the ioctl
returns the EINVAL error code. For more information on cropping
The ``audios`` field was replaced by ``capabilities`` flag
``V4L2_CAP_AUDIO``, indicating *if* the device has any audio inputs or
outputs. To determine their number applications can enumerate audio
-inputs with the :ref:`VIDIOC_G_AUDIO` ioctl. The
+inputs with the :ref:`VIDIOC_G_AUDIO <VIDIOC_G_AUDIO>` ioctl. The
audio ioctls are described in :ref:`audio`.
The ``maxwidth``, ``maxheight``, ``minwidth`` and ``minheight`` fields
:c:type:`struct video_channel` to enumerate the video inputs of a V4L
device. The equivalent V4L2 ioctls are
:ref:`VIDIOC_ENUMINPUT`,
-:ref:`VIDIOC_G_INPUT` and
+:ref:`VIDIOC_G_INPUT <VIDIOC_G_INPUT>` and
:ref:`VIDIOC_S_INPUT <VIDIOC_G_INPUT>` using struct
:ref:`v4l2_input <v4l2-input>` as discussed in :ref:`video`.
The V4L ``VIDIOCGTUNER`` and ``VIDIOCSTUNER`` ioctl and struct
:c:type:`struct video_tuner` can be used to enumerate the tuners of a
V4L TV or radio device. The equivalent V4L2 ioctls are
-:ref:`VIDIOC_G_TUNER` and
+:ref:`VIDIOC_G_TUNER <VIDIOC_G_TUNER>` and
:ref:`VIDIOC_S_TUNER <VIDIOC_G_TUNER>` using struct
:ref:`v4l2_tuner <v4l2-tuner>`. Tuners are covered in :ref:`tuner`.
The ``VIDIOCGFREQ`` and ``VIDIOCSFREQ`` ioctl to change the tuner
frequency where renamed to
-:ref:`VIDIOC_G_FREQUENCY` and
+:ref:`VIDIOC_G_FREQUENCY <VIDIOC_G_FREQUENCY>` and
:ref:`VIDIOC_S_FREQUENCY <VIDIOC_G_FREQUENCY>`. They take a pointer
to a struct :ref:`v4l2_frequency <v4l2-frequency>` instead of an
unsigned long integer.
and struct :c:type:`struct video_picture`. The following fields where
replaced by V4L2 controls accessible with the
:ref:`VIDIOC_QUERYCTRL`,
-:ref:`VIDIOC_G_CTRL` and
+:ref:`VIDIOC_G_CTRL <VIDIOC_G_CTRL>` and
:ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` ioctls:
The ``VIDIOCGAUDIO`` and ``VIDIOCSAUDIO`` ioctl and struct
:c:type:`struct video_audio` are used to enumerate the audio inputs
of a V4L device. The equivalent V4L2 ioctls are
-:ref:`VIDIOC_G_AUDIO` and
+:ref:`VIDIOC_G_AUDIO <VIDIOC_G_AUDIO>` and
:ref:`VIDIOC_S_AUDIO <VIDIOC_G_AUDIO>` using struct
:ref:`v4l2_audio <v4l2-audio>` as discussed in :ref:`audio`.
The following fields where replaced by V4L2 controls accessible with the
:ref:`VIDIOC_QUERYCTRL`,
-:ref:`VIDIOC_G_CTRL` and
+:ref:`VIDIOC_G_CTRL <VIDIOC_G_CTRL>` and
:ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` ioctls:
====================
The V4L2 ioctls equivalent to ``VIDIOCGFBUF`` and ``VIDIOCSFBUF`` are
-:ref:`VIDIOC_G_FBUF` and
+:ref:`VIDIOC_G_FBUF <VIDIOC_G_FBUF>` and
:ref:`VIDIOC_S_FBUF <VIDIOC_G_FBUF>`. The ``base`` field of struct
:c:type:`struct video_buffer` remained unchanged, except V4L2 defines
a flag to indicate non-destructive overlays instead of a ``NULL``
Instead of the special ioctls ``VIDIOCGWIN`` and ``VIDIOCSWIN`` V4L2
uses the general-purpose data format negotiation ioctls
-:ref:`VIDIOC_G_FMT` and
+:ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` and
:ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>`. They take a pointer to a struct
:ref:`v4l2_format <v4l2-format>` as argument. Here the ``win`` member
of the ``fmt`` union is used, a struct
To capture only a subsection of the full picture V4L defines the
``VIDIOCGCAPTURE`` and ``VIDIOCSCAPTURE`` ioctls using struct
:c:type:`struct video_capture`. The equivalent V4L2 ioctls are
-:ref:`VIDIOC_G_CROP` and
+:ref:`VIDIOC_G_CROP <VIDIOC_G_CROP>` and
:ref:`VIDIOC_S_CROP <VIDIOC_G_CROP>` using struct
:ref:`v4l2_crop <v4l2-crop>`, and the related
:ref:`VIDIOC_CROPCAP` ioctl. This is a rather
To select an image format and size, V4L provides the ``VIDIOCSPICT`` and
``VIDIOCSWIN`` ioctls. V4L2 uses the general-purpose data format
-negotiation ioctls :ref:`VIDIOC_G_FMT` and
+negotiation ioctls :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` and
:ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>`. They take a pointer to a struct
:ref:`v4l2_format <v4l2-format>` as argument, here the struct
:ref:`v4l2_pix_format <v4l2-pix-format>` named ``pix`` of its
DV timings for the device applications use the
:ref:`VIDIOC_S_DV_TIMINGS <VIDIOC_G_DV_TIMINGS>` ioctl and to get
current DV timings they use the
-:ref:`VIDIOC_G_DV_TIMINGS` ioctl. To detect
+:ref:`VIDIOC_G_DV_TIMINGS <VIDIOC_G_DV_TIMINGS>` ioctl. To detect
the DV timings as seen by the video receiver applications use the
:ref:`VIDIOC_QUERY_DV_TIMINGS` ioctl.
========================
Three new ioctls are available:
-:ref:`VIDIOC_G_EXT_CTRLS`,
+:ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>`,
:ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` and
:ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>`. These ioctls act
on arrays of controls (as opposed to the
-:ref:`VIDIOC_G_CTRL` and
+:ref:`VIDIOC_G_CTRL <VIDIOC_G_CTRL>` and
:ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` ioctls that act on a single
control). This is needed since it is often required to atomically change
several controls at once.
A single mechanism exists to negotiate all data formats using the
aggregate struct :ref:`v4l2_format <v4l2-format>` and the
-:ref:`VIDIOC_G_FMT` and
+:ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` and
:ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctls. Additionally the
:ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>` ioctl can be used to examine
what the hardware *could* do, without actually selecting a new data
*may* support a switch using :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>`.
All drivers exchanging data with applications must support the
-:ref:`VIDIOC_G_FMT` and :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl. Implementation of the
+:ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` and :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl. Implementation of the
:ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>` is highly recommended but optional.
depends on the discarding policy.
Applications can get and set the number of buffers used internally by
-the driver with the :ref:`VIDIOC_G_PARM` and
+the driver with the :ref:`VIDIOC_G_PARM <VIDIOC_G_PARM>` and
:ref:`VIDIOC_S_PARM <VIDIOC_G_PARM>` ioctls. They are optional,
however. The discarding policy is not reported and cannot be changed.
For minimum requirements see :ref:`devices`.
:c:type:`struct video_standard` and the color subcarrier fields were
renamed. The :ref:`VIDIOC_QUERYSTD` ioctl was
renamed to :ref:`VIDIOC_ENUMSTD`,
-:ref:`VIDIOC_G_INPUT` to
+:ref:`VIDIOC_G_INPUT <VIDIOC_G_INPUT>` to
:ref:`VIDIOC_ENUMINPUT`. A first draft of the
Codec API was released.
1998-11-14: ``V4L2_PIX_FMT_RGB24`` changed to ``V4L2_PIX_FMT_BGR24``,
and ``V4L2_PIX_FMT_RGB32`` changed to ``V4L2_PIX_FMT_BGR32``. Audio
controls are now accessible with the
-:ref:`VIDIOC_G_CTRL` and
+:ref:`VIDIOC_G_CTRL <VIDIOC_G_CTRL>` and
:ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` ioctls under names starting
with ``V4L2_CID_AUDIO``. The ``V4L2_MAJOR`` define was removed from
``videodev.h`` since it was only used once in the ``videodev`` kernel
int a = V4L2_XXX; err = ioctl(fd, VIDIOC_XXX, &a);
4. All the different get- and set-format commands were swept into one
- :ref:`VIDIOC_G_FMT` and
+ :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` and
:ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl taking a union and a
type field selecting the union member as parameter. Purpose is to
simplify the API by eliminating several ioctls and to allow new and
2001-04-13: Big endian 16-bit RGB formats were added.
2001-09-17: New YUV formats and the
-:ref:`VIDIOC_G_FREQUENCY` and
+:ref:`VIDIOC_G_FREQUENCY <VIDIOC_G_FREQUENCY>` and
:ref:`VIDIOC_S_FREQUENCY <VIDIOC_G_FREQUENCY>` ioctls were added.
(The old ``VIDIOC_G_FREQ`` and ``VIDIOC_S_FREQ`` ioctls did not take
multiple tuners into account.)
2000-09-18: ``V4L2_BUF_TYPE_VBI`` was added. This may *break
-compatibility* as the :ref:`VIDIOC_G_FMT` and
+compatibility* as the :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` and
:ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctls may fail now if the struct
:c:type:`struct v4l2_fmt` ``type`` field does not contain
``V4L2_BUF_TYPE_VBI``. In the documentation of the struct
supported standards with an ioctl applications can now refer to
standards by :ref:`v4l2_std_id <v4l2-std-id>` and symbols
defined in the ``videodev2.h`` header file. For details see
- :ref:`standard`. The :ref:`VIDIOC_G_STD` and
+ :ref:`standard`. The :ref:`VIDIOC_G_STD <VIDIOC_G_STD>` and
:ref:`VIDIOC_S_STD <VIDIOC_G_STD>` now take a pointer to this
type as argument. :ref:`VIDIOC_QUERYSTD` was
added to autodetect the received standard, if the hardware has this
3. The audio input and output interface was found to be incomplete.
- Previously the :ref:`VIDIOC_G_AUDIO` ioctl would
+ Previously the :ref:`VIDIOC_G_AUDIO <VIDIOC_G_AUDIO>` ioctl would
enumerate the available audio inputs. An ioctl to determine the
current audio input, if more than one combines with the current video
input, did not exist. So ``VIDIOC_G_AUDIO`` was renamed to
``VIDIOC_G_AUDIO_OLD``, this ioctl was removed on Kernel 2.6.39. The
:ref:`VIDIOC_ENUMAUDIO` ioctl was added to
enumerate audio inputs, while
- :ref:`VIDIOC_G_AUDIO` now reports the current
+ :ref:`VIDIOC_G_AUDIO <VIDIOC_G_AUDIO>` now reports the current
audio input.
The same changes were made to
2. A new ``V4L2_TUNER_MODE_LANG1_LANG2`` was defined to record both
languages of a bilingual program. The use of
``V4L2_TUNER_MODE_STEREO`` for this purpose is deprecated now. See
- the :ref:`VIDIOC_G_TUNER` section for details.
+ the :ref:`VIDIOC_G_TUNER <VIDIOC_G_TUNER>` section for details.
V4L2 spec erratum 2006-09-23 (Draft 0.15)
``V4L2_BUF_TYPE_SLICED_VBI_OUTPUT`` of the sliced VBI interface were
not mentioned along with other buffer types.
-2. In :ref:`VIDIOC_G_AUDIO` it was clarified that the struct
+2. In :ref:`VIDIOC_G_AUDIO <VIDIOC_G_AUDIO>` it was clarified that the struct
:ref:`v4l2_audio <v4l2-audio>` ``mode`` field is a flags field.
3. :ref:`VIDIOC_QUERYCAP` did not mention the sliced VBI and radio
capability flags.
-4. In :ref:`VIDIOC_G_FREQUENCY` it was clarified that applications
+4. In :ref:`VIDIOC_G_FREQUENCY <VIDIOC_G_FREQUENCY>` it was clarified that applications
must initialize the tuner ``type`` field of struct
:ref:`v4l2_frequency <v4l2-frequency>` before calling
:ref:`VIDIOC_S_FREQUENCY <VIDIOC_G_FREQUENCY>`.
V4L2 in Linux 2.6.18
====================
-1. New ioctls :ref:`VIDIOC_G_EXT_CTRLS`,
+1. New ioctls :ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>`,
:ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` and
:ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` were added, a
flag to skip unsupported controls with
buffer type field was added replacing a reserved field. Note on
architectures where the size of enum types differs from int types the
size of the structure changed. The
- :ref:`VIDIOC_G_SLICED_VBI_CAP` ioctl
+ :ref:`VIDIOC_G_SLICED_VBI_CAP <VIDIOC_G_SLICED_VBI_CAP>` ioctl
was redefined from being read-only to write-read. Applications must
initialize the type field and clear the reserved fields now. These
changes may *break the compatibility* with older drivers and
2. Three new clipping/blending methods with a global or straight or
inverted local alpha value were added to the video overlay interface.
- See the description of the :ref:`VIDIOC_G_FBUF`
+ See the description of the :ref:`VIDIOC_G_FBUF <VIDIOC_G_FBUF>`
and :ref:`VIDIOC_S_FBUF <VIDIOC_G_FBUF>` ioctls for details.
A new ``global_alpha`` field was added to
In most cases, libv4l2 just passes the calls directly through to the
v4l2 driver, intercepting the calls to
:ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>`,
-:ref:`VIDIOC_G_FMT`
+:ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>`
:ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>`
:ref:`VIDIOC_ENUM_FRAMESIZES` and
:ref:`VIDIOC_ENUM_FRAMEINTERVALS` in
- 'JPEG'
- - TBD. See also :ref:`VIDIOC_G_JPEGCOMP`,
+ - TBD. See also :ref:`VIDIOC_G_JPEGCOMP <VIDIOC_G_JPEGCOMP>`,
:ref:`VIDIOC_S_JPEGCOMP <VIDIOC_G_JPEGCOMP>`.
- .. _`V4L2-PIX-FMT-MPEG`:
version (see :ref:`planar-apis`). Image formats are negotiated with
the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl. (The explanations here
focus on video capturing and output, for overlay frame buffer formats
-see also :ref:`VIDIOC_G_FBUF`.)
+see also :ref:`VIDIOC_G_FBUF <VIDIOC_G_FBUF>`.)
.. toctree::
together with non-multi-planar ones for devices that handle both
single- and multi-planar formats.
-:ref:`VIDIOC_G_FMT`,
+:ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>`,
:ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>`,
:ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>`
New structures for describing multi-planar formats are added: struct
"NTSC-M" and "SECAM-D/K". [1]_
To query and select the standard used by the current video input or
-output applications call the :ref:`VIDIOC_G_STD` and
+output applications call the :ref:`VIDIOC_G_STD <VIDIOC_G_STD>` and
:ref:`VIDIOC_S_STD <VIDIOC_G_STD>` ioctl, respectively. The
*received* standard can be sensed with the
:ref:`VIDIOC_QUERYSTD` ioctl. Note that the
Here the driver shall set the ``std`` field of struct
:ref:`v4l2_input <v4l2-input>` and struct
-:ref:`v4l2_output <v4l2-output>` to zero and the :ref:`VIDIOC_G_STD`,
+:ref:`v4l2_output <v4l2-output>` to zero and the :ref:`VIDIOC_G_STD <VIDIOC_G_STD>`,
:ref:`VIDIOC_S_STD <VIDIOC_G_STD>`, :ref:`VIDIOC_QUERYSTD` and :ref:`VIDIOC_ENUMSTD` ioctls
shall return the ENOTTY error code or the EINVAL error code.
section discussing the :ref:`read() <func-read>` function.
To get and set the streaming parameters applications call the
-:ref:`VIDIOC_G_PARM` and
+:ref:`VIDIOC_G_PARM <VIDIOC_G_PARM>` and
:ref:`VIDIOC_S_PARM <VIDIOC_G_PARM>` ioctl, respectively. They take
a pointer to a struct :ref:`v4l2_streamparm <v4l2-streamparm>`, which
contains a union holding separate parameters for input and output
inputs.
To query and change tuner properties applications use the
-:ref:`VIDIOC_G_TUNER` and
+:ref:`VIDIOC_G_TUNER <VIDIOC_G_TUNER>` and
:ref:`VIDIOC_S_TUNER <VIDIOC_G_TUNER>` ioctls, respectively. The
-struct :ref:`v4l2_tuner <v4l2-tuner>` returned by :ref:`VIDIOC_G_TUNER`
+struct :ref:`v4l2_tuner <v4l2-tuner>` returned by :ref:`VIDIOC_G_TUNER <VIDIOC_G_TUNER>`
also contains signal status information applicable when the tuner of the
current video or radio input is queried. Note that :ref:`VIDIOC_S_TUNER <VIDIOC_G_TUNER>`
does not switch the current tuner, when there is more than one at all.
cannot specify whether the frequency is for a tuner or a modulator.
To query and change modulator properties applications use the
-:ref:`VIDIOC_G_MODULATOR` and
+:ref:`VIDIOC_G_MODULATOR <VIDIOC_G_MODULATOR>` and
:ref:`VIDIOC_S_MODULATOR <VIDIOC_G_MODULATOR>` ioctl. Note that
:ref:`VIDIOC_S_MODULATOR <VIDIOC_G_MODULATOR>` does not switch the current modulator, when there
is more than one at all. The modulator is solely determined by the
===============
To get and set the tuner or modulator radio frequency applications use
-the :ref:`VIDIOC_G_FREQUENCY` and
+the :ref:`VIDIOC_G_FREQUENCY <VIDIOC_G_FREQUENCY>` and
:ref:`VIDIOC_S_FREQUENCY <VIDIOC_G_FREQUENCY>` ioctl which both take
a pointer to a struct :ref:`v4l2_frequency <v4l2-frequency>`. These
ioctls are used for TV and radio devices alike. Drivers must support
:ref:`VIDIOC_ENUMINPUT` ioctl also contains signal
:status information applicable when the current video input is queried.
-The :ref:`VIDIOC_G_INPUT` and
-:ref:`VIDIOC_G_OUTPUT` ioctls return the index of
+The :ref:`VIDIOC_G_INPUT <VIDIOC_G_INPUT>` and
+:ref:`VIDIOC_G_OUTPUT <VIDIOC_G_OUTPUT>` ioctls return the index of
the current video input or output. To select a different input or output
applications call the :ref:`VIDIOC_S_INPUT <VIDIOC_G_INPUT>` and
:ref:`VIDIOC_S_OUTPUT <VIDIOC_G_OUTPUT>` ioctls. Drivers must
able to handle. The application has to fill in this struct
:ref:`v4l2_format <v4l2-format>`. Usually this will be done using the
:ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>` or
-:ref:`VIDIOC_G_FMT` ioctls to ensure that the
+:ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` ioctls to ensure that the
requested format is supported by the driver. Based on the format's
``type`` field the requested buffer size (for single-planar) or plane
sizes (for multi-planar formats) will be used for the allocated buffers.
bounds. To enumerate all audio inputs applications shall begin at index
zero, incrementing by one until the driver returns EINVAL.
-See :ref:`VIDIOC_G_AUDIO` for a description of struct
+See :ref:`VIDIOC_G_AUDIO <VIDIOC_G_AUDIO>` for a description of struct
:ref:`v4l2_audio <v4l2-audio>`.
Note connectors on a TV card to loop back the received audio signal to a
sound card are not audio outputs in this sense.
-See :ref:`VIDIOC_G_AUDIOout` for a description of struct
+See :ref:`VIDIOC_G_AUDIOout <VIDIOC_G_AUDIOout>` for a description of struct
:ref:`v4l2_audioout <v4l2-audioout>`.
.. [1]
The supported standards may overlap and we need an unambiguous set to
- find the current standard returned by :ref:`VIDIOC_G_STD`.
+ find the current standard returned by :ref:`VIDIOC_G_STD <VIDIOC_G_STD>`.
.. [2]
Japan uses a standard similar to M/NTSC (V4L2_STD_NTSC_M_JP).
To query the current audio input applications zero out the ``reserved``
array of a struct :ref:`v4l2_audio <v4l2-audio>` and call the
-:ref:`VIDIOC_G_AUDIO` ioctl with a pointer to this structure. Drivers fill
+:ref:`VIDIOC_G_AUDIO <VIDIOC_G_AUDIO>` ioctl with a pointer to this structure. Drivers fill
the rest of the structure or return an EINVAL error code when the device
has no audio inputs, or none which combine with the current video input.
To query the cropping rectangle size and position applications set the
``type`` field of a :c:type:`struct v4l2_crop` structure to the
-respective buffer (stream) type and call the :ref:`VIDIOC_G_CROP` ioctl
+respective buffer (stream) type and call the :ref:`VIDIOC_G_CROP <VIDIOC_G_CROP>` ioctl
with a pointer to this structure. The driver fills the rest of the
structure or returns the EINVAL error code if cropping is not supported.
Finally the driver programs the hardware with the actual cropping and
image parameters. :ref:`VIDIOC_S_CROP <VIDIOC_G_CROP>` is a write-only ioctl, it does not
return the actual parameters. To query them applications must call
-:ref:`VIDIOC_G_CROP` and :ref:`VIDIOC_G_FMT`. When the
+:ref:`VIDIOC_G_CROP <VIDIOC_G_CROP>` and :ref:`VIDIOC_G_FMT`. When the
parameters are unsuitable the application may modify the cropping or
image parameters and repeat the cycle until satisfactory parameters have
been negotiated.
To get the current value of a control applications initialize the ``id``
field of a struct :c:type:`struct v4l2_control` and call the
-:ref:`VIDIOC_G_CTRL` ioctl with a pointer to this structure. To change the
+:ref:`VIDIOC_G_CTRL <VIDIOC_G_CTRL>` ioctl with a pointer to this structure. To change the
value of a control applications initialize the ``id`` and ``value``
fields of a struct :c:type:`struct v4l2_control` and call the
:ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` ioctl.
EINVAL error code is returned as well.
These ioctls work only with user controls. For other control classes the
-:ref:`VIDIOC_G_EXT_CTRLS`,
+:ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>`,
:ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` or
:ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` must be used.
To set DV timings for the input or output, applications use the
:ref:`VIDIOC_S_DV_TIMINGS <VIDIOC_G_DV_TIMINGS>` ioctl and to get the current timings,
-applications use the :ref:`VIDIOC_G_DV_TIMINGS` ioctl. The detailed timing
+applications use the :ref:`VIDIOC_G_DV_TIMINGS <VIDIOC_G_DV_TIMINGS>` ioctl. The detailed timing
information is filled in using the structure struct
:ref:`v4l2_dv_timings <v4l2-dv-timings>`. These ioctls take a
pointer to the struct :ref:`v4l2_dv_timings <v4l2-dv-timings>`
To get the EDID data the application has to fill in the ``pad``,
``start_block``, ``blocks`` and ``edid`` fields, zero the ``reserved``
-array and call :ref:`VIDIOC_G_EDID`. The current EDID from block
+array and call :ref:`VIDIOC_G_EDID <VIDIOC_G_EDID>`. The current EDID from block
``start_block`` and of size ``blocks`` will be placed in the memory
``edid`` points to. The ``edid`` pointer must point to memory at least
``blocks`` * 128 bytes large (the size of one block is 128 bytes).
until they have been read.
If ``start_block`` and ``blocks`` are both set to 0 when
-:ref:`VIDIOC_G_EDID` is called, then the driver will set ``blocks`` to the
+:ref:`VIDIOC_G_EDID <VIDIOC_G_EDID>` is called, then the driver will set ``blocks`` to the
total number of available EDID blocks and it will return 0 without
copying any data. This is an easy way to discover how many EDID blocks
there are. Note that if there are no EDID blocks available at all, then
Description
===========
-The :ref:`VIDIOC_G_ENC_INDEX` ioctl provides meta data about a compressed
+The :ref:`VIDIOC_G_ENC_INDEX <VIDIOC_G_ENC_INDEX>` ioctl provides meta data about a compressed
video stream the same or another application currently reads from the
driver, which is useful for random access into the stream without
decoding it.
-To read the data applications must call :ref:`VIDIOC_G_ENC_INDEX` with a
+To read the data applications must call :ref:`VIDIOC_G_ENC_INDEX <VIDIOC_G_ENC_INDEX>` with a
pointer to a struct :ref:`v4l2_enc_idx <v4l2-enc-idx>`. On success
the driver fills the ``entry`` array, stores the number of elements
written in the ``entries`` field, and initializes the ``entries_cap``
field.
Each element of the ``entry`` array contains meta data about one
-picture. A :ref:`VIDIOC_G_ENC_INDEX` call reads up to
+picture. A :ref:`VIDIOC_G_ENC_INDEX <VIDIOC_G_ENC_INDEX>` call reads up to
``V4L2_ENC_IDX_ENTRIES`` entries from a driver buffer, which can hold up
to ``entries_cap`` entries. This number can be lower or higher than
``V4L2_ENC_IDX_ENTRIES``, but not zero. When the application fails to
To get the current value of a set of controls applications initialize
the ``id``, ``size`` and ``reserved2`` fields of each struct
:ref:`v4l2_ext_control <v4l2-ext-control>` and call the
-:ref:`VIDIOC_G_EXT_CTRLS` ioctl. String controls controls must also set the
+:ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` ioctl. String controls controls must also set the
``string`` field. Controls of compound types
(``V4L2_CTRL_FLAG_HAS_PAYLOAD`` is set) must set the ``ptr`` field.
- The total size in bytes of the payload of this control. This is
normally 0, but for pointer controls this should be set to the
size of the memory containing the payload, or that will receive
- the payload. If :ref:`VIDIOC_G_EXT_CTRLS` finds that this value is
+ the payload. If :ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` finds that this value is
less than is required to store the payload result, then it is set
to a value large enough to store the payload result and ENOSPC is
returned. Note that for string controls this ``size`` field should
:ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` fails with ``error_idx`` set to ``count``,
then you can call :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` to try to discover the
actual control that failed the validation step. Unfortunately,
- there is no ``TRY`` equivalent for :ref:`VIDIOC_G_EXT_CTRLS`.
+ there is no ``TRY`` equivalent for :ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>`.
- .. row 6
- The class containing user controls. These controls are described
in :ref:`control`. All controls that can be set using the
:ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` and
- :ref:`VIDIOC_G_CTRL` ioctl belong to this
+ :ref:`VIDIOC_G_CTRL <VIDIOC_G_CTRL>` ioctl belong to this
class.
- .. row 2
Description
===========
-Applications can use the :ref:`VIDIOC_G_FBUF` and :ref:`VIDIOC_S_FBUF <VIDIOC_G_FBUF>` ioctl
+Applications can use the :ref:`VIDIOC_G_FBUF <VIDIOC_G_FBUF>` and :ref:`VIDIOC_S_FBUF <VIDIOC_G_FBUF>` ioctl
to get and set the framebuffer parameters for a
:ref:`Video Overlay <overlay>` or :ref:`Video Output Overlay <osd>`
(OSD). The type of overlay is implied by the device type (capture or
VGA signal or graphics into a video signal. *Video Output Overlays* are
always non-destructive.
-To get the current parameters applications call the :ref:`VIDIOC_G_FBUF`
+To get the current parameters applications call the :ref:`VIDIOC_G_FBUF <VIDIOC_G_FBUF>`
ioctl with a pointer to a :c:type:`struct v4l2_framebuffer`
structure. The driver fills all fields of the structure or returns an
EINVAL error code when overlays are not supported.
implemented on the TV card all other parameters are determined by the
driver. When an application calls :ref:`VIDIOC_S_FBUF <VIDIOC_G_FBUF>` with a pointer to
this structure, the driver prepares for the overlay and returns the
-framebuffer parameters as :ref:`VIDIOC_G_FBUF` does, or it returns an error
+framebuffer parameters as :ref:`VIDIOC_G_FBUF <VIDIOC_G_FBUF>` does, or it returns an error
code.
To set the parameters for a *non-destructive Video Overlay*,
applications must initialize the ``flags`` field, the ``fmt``
substructure, and call :ref:`VIDIOC_S_FBUF <VIDIOC_G_FBUF>`. Again the driver prepares for
-the overlay and returns the framebuffer parameters as :ref:`VIDIOC_G_FBUF`
+the overlay and returns the framebuffer parameters as :ref:`VIDIOC_G_FBUF <VIDIOC_G_FBUF>`
does, or it returns an error code.
For a *destructive Video Overlay* applications must additionally provide
type. For example video capture devices use
``V4L2_BUF_TYPE_VIDEO_CAPTURE`` or
``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE``. When the application calls the
-:ref:`VIDIOC_G_FMT` ioctl with a pointer to this structure the driver fills
+:ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` ioctl with a pointer to this structure the driver fills
the respective member of the ``fmt`` union. In case of video capture
devices that is either the struct
:ref:`v4l2_pix_format <v4l2-pix-format>` ``pix`` or the struct
parameters acceptable for both the application and driver. On success
the driver may program the hardware, allocate resources and generally
prepare for data exchange. Finally the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl returns
-the current format parameters as :ref:`VIDIOC_G_FMT` does. Very simple,
+the current format parameters as :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` does. Very simple,
inflexible devices may even ignore all input and always return the
default parameters. However all V4L2 devices exchanging data with the
-application must implement the :ref:`VIDIOC_G_FMT` and :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>`
+application must implement the :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` and :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>`
ioctl. When the requested buffer type is not supported drivers return an
EINVAL error code on a :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` attempt. When I/O is already in
progress or the resource is not available for other reasons drivers
:ref:`v4l2_frequency <v4l2-frequency>` to the respective tuner or
modulator number (only input devices have tuners, only output devices
have modulators), zero out the ``reserved`` array and call the
-:ref:`VIDIOC_G_FREQUENCY` ioctl with a pointer to this structure. The
+:ref:`VIDIOC_G_FREQUENCY <VIDIOC_G_FREQUENCY>` ioctl with a pointer to this structure. The
driver stores the current frequency in the ``frequency`` field.
To change the current tuner or modulator radio frequency applications
===========
To query the current video input applications call the
-:ref:`VIDIOC_G_INPUT` ioctl with a pointer to an integer where the driver
+:ref:`VIDIOC_G_INPUT <VIDIOC_G_INPUT>` ioctl with a pointer to an integer where the driver
stores the number of the input, as in the struct
:ref:`v4l2_input <v4l2-input>` ``index`` field. This ioctl will fail
only when there are no video inputs, returning EINVAL.
To query the attributes of a modulator applications initialize the
``index`` field and zero out the ``reserved`` array of a struct
:ref:`v4l2_modulator <v4l2-modulator>` and call the
-:ref:`VIDIOC_G_MODULATOR` ioctl with a pointer to this structure. Drivers
+:ref:`VIDIOC_G_MODULATOR <VIDIOC_G_MODULATOR>` ioctl with a pointer to this structure. Drivers
fill the rest of the structure or return an EINVAL error code when the
index is out of bounds. To enumerate all modulators applications shall
begin at index zero, incrementing by one until the driver returns
===========
To query the current video output applications call the
-:ref:`VIDIOC_G_OUTPUT` ioctl with a pointer to an integer where the driver
+:ref:`VIDIOC_G_OUTPUT <VIDIOC_G_OUTPUT>` ioctl with a pointer to an integer where the driver
stores the number of the output, as in the struct
:ref:`v4l2_output <v4l2-output>` ``index`` field. This ioctl will
fail only when there are no video outputs, returning the EINVAL error
section discussing the :ref:`read() <func-read>` function.
To get and set the streaming parameters applications call the
-:ref:`VIDIOC_G_PARM` and :ref:`VIDIOC_S_PARM <VIDIOC_G_PARM>` ioctl, respectively. They take a
+:ref:`VIDIOC_G_PARM <VIDIOC_G_PARM>` and :ref:`VIDIOC_S_PARM <VIDIOC_G_PARM>` ioctl, respectively. They take a
pointer to a struct :c:type:`struct v4l2_streamparm` which contains a
union holding separate parameters for input and output devices.
===========
To query the current access priority applications call the
-:ref:`VIDIOC_G_PRIORITY` ioctl with a pointer to an enum v4l2_priority
+:ref:`VIDIOC_G_PRIORITY <VIDIOC_G_PRIORITY>` ioctl with a pointer to an enum v4l2_priority
variable where the driver stores the current priority.
To request an access priority applications store the desired priority in
To find out which data services are supported by a sliced VBI capture or
output device, applications initialize the ``type`` field of a struct
:ref:`v4l2_sliced_vbi_cap <v4l2-sliced-vbi-cap>`, clear the
-``reserved`` array and call the :ref:`VIDIOC_G_SLICED_VBI_CAP` ioctl. The
+``reserved`` array and call the :ref:`VIDIOC_G_SLICED_VBI_CAP <VIDIOC_G_SLICED_VBI_CAP>` ioctl. The
driver fills in the remaining fields or returns an EINVAL error code if
the sliced VBI API is unsupported or ``type`` is invalid.
===========
To query and select the current video standard applications use the
-:ref:`VIDIOC_G_STD` and :ref:`VIDIOC_S_STD <VIDIOC_G_STD>` ioctls which take a pointer to a
-:ref:`v4l2_std_id <v4l2-std-id>` type as argument. :ref:`VIDIOC_G_STD`
+:ref:`VIDIOC_G_STD <VIDIOC_G_STD>` and :ref:`VIDIOC_S_STD <VIDIOC_G_STD>` ioctls which take a pointer to a
+:ref:`v4l2_std_id <v4l2-std-id>` type as argument. :ref:`VIDIOC_G_STD <VIDIOC_G_STD>`
can return a single flag or a set of flags as in struct
:ref:`v4l2_standard <v4l2-standard>` field ``id``. The flags must be
unambiguous such that they appear in only one enumerated
:c:type:`struct v4l2_standard` structure.
:ref:`VIDIOC_S_STD <VIDIOC_G_STD>` accepts one or more flags, being a write-only ioctl it
-does not return the actual new standard as :ref:`VIDIOC_G_STD` does. When
+does not return the actual new standard as :ref:`VIDIOC_G_STD <VIDIOC_G_STD>` does. When
no flags are given or the current input does not support the requested
standard the driver returns an EINVAL error code. When the standard set
is ambiguous drivers may return EINVAL or choose any of the requested
:ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` you need to
set the ``size`` field of struct
:ref:`v4l2_ext_control <v4l2-ext-control>` to 9. For
- :ref:`VIDIOC_G_EXT_CTRLS` you can set
+ :ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` you can set
the ``size`` field to ``maximum`` + 1. Which character encoding is
used will depend on the string control itself and should be part
of the control documentation.
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