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 ``VIDIOC_G_FMT``, and call the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>`
+of :ref:`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 ``VIDIOC_G_FMT``
+parameters and finally return the actual parameters as :ref:`VIDIOC_G_FMT`
does.
-Like ``VIDIOC_S_FMT`` the :ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>` ioctl
+Like :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` the :ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>` ioctl
can be used to learn about hardware limitations without disabling I/O or
possibly time consuming hardware preparations.
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
-``VIDIOC_G_FMT``, ``VIDIOC_S_FMT`` and ``VIDIOC_TRY_FMT`` ioctls for
-details. Video capture devices must implement both the ``VIDIOC_G_FMT``
-and ``VIDIOC_S_FMT`` ioctl, even if ``VIDIOC_S_FMT`` ignores all
-requests and always returns default parameters as ``VIDIOC_G_FMT`` does.
-``VIDIOC_TRY_FMT`` is optional.
+: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`
+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.
+:ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>` is optional.
Reading Images
``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 ``VIDIOC_G_FMT`` does. Like ``VIDIOC_S_FMT``,
+the actual parameters as :ref:`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
-``VIDIOC_S_FMT`` this also works after the overlay has been enabled.
+:ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` this also works after the overlay has been enabled.
A struct :ref:`v4l2_crop <v4l2-crop>` defines the size and position
of the target rectangle. The scaling factor of the overlay is implied by
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 ``VIDIOC_G_FMT``, and call the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>`
+of :ref:`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 ``VIDIOC_G_FMT``
+parameters and finally return the actual parameters as :ref:`VIDIOC_G_FMT`
does.
-Like ``VIDIOC_S_FMT`` the :ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>` ioctl
+Like :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` the :ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>` ioctl
can be used to learn about hardware limitations without disabling I/O or
possibly time consuming hardware preparations.
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
-``VIDIOC_G_FMT``, ``VIDIOC_S_FMT`` and ``VIDIOC_TRY_FMT`` ioctls for
-details. Video output devices must implement both the ``VIDIOC_G_FMT``
-and ``VIDIOC_S_FMT`` ioctl, even if ``VIDIOC_S_FMT`` ignores all
-requests and always returns default parameters as ``VIDIOC_G_FMT`` does.
-``VIDIOC_TRY_FMT`` is optional.
+: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`
+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.
+:ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>` is optional.
Writing Images
and the image format, for example RGB 5:6:5. The
:ref:`VIDIOC_G_FBUF` and
:ref:`VIDIOC_S_FBUF <VIDIOC_G_FBUF>` ioctls are available to get and
-set these parameters, respectively. The ``VIDIOC_S_FBUF`` ioctl is
+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,
bypassing the memory protection mechanisms of the kernel. Only the
superuser can change the frame buffer address and size. Users are not
Some devices add the video overlay to the output signal of the graphics
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 ``VIDIOC_S_FBUF`` ioctl is not privileged. An application
-can check for this type of device by calling the ``VIDIOC_G_FBUF``
+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`
ioctl.
A driver may support any (or none) of five clipping/blending methods:
``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 ``VIDIOC_G_FMT`` does. Like ``VIDIOC_S_FMT``, the
+parameters as :ref:`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
-``VIDIOC_S_FMT`` this also works after the overlay has been enabled.
+:ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` this also works after the overlay has been enabled.
The scaling factor of the overlaid image is implied by the width and
height given in struct :ref:`v4l2_window <v4l2-window>` and the size
When the application set the ``clips`` field, this field must
contain the number of clipping rectangles in the list. When clip
lists are not supported the driver ignores this field, its contents
- after calling ``VIDIOC_S_FMT`` are undefined. When clip lists are
+ after calling :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` are undefined. When clip lists are
supported but no clipping is desired this field must be set to zero.
``void * bitmap``
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 ``VIDIOC_G_FMT``, and call the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>`
+of :ref:`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 ``VIDIOC_G_FMT`` and
-``VIDIOC_S_FMT`` ioctl, even if ``VIDIOC_S_FMT`` ignores all requests
-and always returns default parameters as ``VIDIOC_G_FMT`` does.
-``VIDIOC_TRY_FMT`` is optional.
+VBI devices must implement both the :ref:`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.
+:ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>` is optional.
.. _v4l2-vbi-format:
respective device section in :ref:`devices`. For a closer look at
image formats see :ref:`pixfmt`.
-The ``VIDIOC_S_FMT`` ioctl is a major turning-point in the
+The :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl is a major turning-point in the
initialization sequence. Prior to this point multiple panel applications
can access the same device concurrently to select the current input,
-change controls or modify other properties. The first ``VIDIOC_S_FMT``
+change controls or modify other properties. The first :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>`
assigns a logical stream (video data, VBI data etc.) exclusively to one
file descriptor.
simultaneous video capturing may be restricted to the same cropping and
image size.
-When applications omit the ``VIDIOC_S_FMT`` ioctl its locking side
+When applications omit the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl its locking side
effects are implied by the next step, the selection of an I/O method
with the :ref:`VIDIOC_REQBUFS` ioctl or implicit
with the first :ref:`read() <func-read>` or
overlay using the same file descriptor for compatibility with V4L and
earlier versions of V4L2. Switching the logical stream or returning into
"panel mode" is possible by closing and reopening the device. Drivers
-*may* support a switch using ``VIDIOC_S_FMT``.
+*may* support a switch using :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>`.
All drivers exchanging data with applications must support the
-``VIDIOC_G_FMT`` and ``VIDIOC_S_FMT`` ioctl. Implementation of the
-``VIDIOC_TRY_FMT`` is highly recommended but optional.
+:ref:`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.
Image Format Enumeration
the same file descriptor, for compatibility with V4L and earlier
versions of V4L2.
-``VIDIOC_S_FMT`` and ``VIDIOC_REQBUFS`` would permit this to some
+:ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` and :ref:`VIDIOC_REQBUFS` would permit this to some
degree, but for simplicity drivers need not support switching the I/O
method (after first switching away from read/write) other than by
closing and reopening the device.
coordinates are obtained using ``V4L2_SEL_TGT_COMPOSE_BOUNDS``. All
coordinates are expressed in pixels. The rectangle's top/left corner
must be located at position ``(0,0)``. The width and height are equal to
-the image size set by ``VIDIOC_S_FMT``.
+the image size set by :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>`.
The part of a buffer into which the image is inserted by the hardware is
controlled by the ``V4L2_SEL_TGT_COMPOSE`` target. The rectangle's
cropping coordinates are obtained using ``V4L2_SEL_TGT_CROP_BOUNDS``.
All coordinates are expressed in pixels. The top/left corner is always
point ``(0,0)``. The width and height is equal to the image size
-specified using ``VIDIOC_S_FMT`` ioctl.
+specified using :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl.
The top left corner, width and height of the source rectangle, that is
the area from which image date are processed by the hardware, is given
:ref:`v4l2_pix_format <v4l2-pix-format>```::bytesperline``.
Introducing an image offsets could be done by modifying field struct
:ref:`v4l2_buffer <v4l2-buffer>```::m_userptr`` before calling
-``VIDIOC_QBUF``. Those operations should be avoided because they are not
+:ref:`VIDIOC_QBUF`. Those operations should be avoided because they are not
portable (endianness), and do not work for macroblock and Bayer formats
and mmap buffers. The selection API deals with configuration of buffer
cropping/composing in a clear, intuitive and portable way. Next, with
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 ``VIDIOC_G_STD``,
-``VIDIOC_S_STD``, ``VIDIOC_QUERYSTD`` and ``VIDIOC_ENUMSTD`` ioctls
+:ref:`v4l2_output <v4l2-output>` to zero and the :ref:`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.
Applications can make use of the :ref:`input-capabilities` and
To query and change tuner properties applications use the
:ref:`VIDIOC_G_TUNER` and
:ref:`VIDIOC_S_TUNER <VIDIOC_G_TUNER>` ioctls, respectively. The
-struct :ref:`v4l2_tuner <v4l2-tuner>` returned by ``VIDIOC_G_TUNER``
+struct :ref:`v4l2_tuner <v4l2-tuner>` returned by :ref:`VIDIOC_G_TUNER`
also contains signal status information applicable when the tuner of the
-current video or radio input is queried. Note that ``VIDIOC_S_TUNER``
+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.
The tuner is solely determined by the current video input. Drivers must
support both ioctls and set the ``V4L2_CAP_TUNER`` flag in the struct
To query and change modulator properties applications use the
:ref:`VIDIOC_G_MODULATOR` and
:ref:`VIDIOC_S_MODULATOR <VIDIOC_G_MODULATOR>` ioctl. Note that
-``VIDIOC_S_MODULATOR`` does not switch the current modulator, when there
+: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
current video output. Drivers must support both ioctls and set the
``V4L2_CAP_MODULATOR`` flag in the struct
- ``count``
- The number of buffers requested or granted. If count == 0, then
- ``VIDIOC_CREATE_BUFS`` will set ``index`` to the current number of
+ :ref:`VIDIOC_CREATE_BUFS` will set ``index`` to the current number of
created buffers, and it will check the validity of ``memory`` and
``format.type``. If those are invalid -1 is returned and errno is
- set to EINVAL error code, otherwise ``VIDIOC_CREATE_BUFS`` returns
+ set to EINVAL error code, otherwise :ref:`VIDIOC_CREATE_BUFS` returns
0. It will never set errno to EBUSY error code in this particular
case.
Applications use this function to query the cropping limits, the pixel
aspect of images and to calculate scale factors. They set the ``type``
field of a v4l2_cropcap structure to the respective buffer (stream)
-type and call the ``VIDIOC_CROPCAP`` ioctl with a pointer to this
+type and call the :ref:`VIDIOC_CROPCAP` ioctl with a pointer to this
structure. Drivers fill the rest of the structure. The results are
constant except when switching the video standard. Remember this switch
can occur implicit when switching the video input or output.
To query the driver applications must initialize the ``match.type`` and
``match.addr`` or ``match.name`` fields of a struct
:ref:`v4l2_dbg_chip_info <v4l2-dbg-chip-info>` and call
-``VIDIOC_DBG_G_CHIP_INFO`` with a pointer to this structure. On success
+:ref:`VIDIOC_DBG_G_CHIP_INFO` with a pointer to this structure. On success
the driver stores information about the selected chip in the ``name``
and ``flags`` fields.
When ``match.type`` is ``V4L2_CHIP_MATCH_BRIDGE``, ``match.addr``
selects the nth bridge 'chip' on the TV card. You can enumerate all
chips by starting at zero and incrementing ``match.addr`` by one until
-``VIDIOC_DBG_G_CHIP_INFO`` fails with an EINVAL error code. The number
+:ref:`VIDIOC_DBG_G_CHIP_INFO` fails with an EINVAL error code. The number
zero always selects the bridge chip itself, e. g. the chip connected to
the PCI or USB bus. Non-zero numbers identify specific parts of the
bridge chip such as an AC97 register block.
To enumerate image formats applications initialize the ``type`` and
``index`` field of struct :ref:`v4l2_fmtdesc <v4l2-fmtdesc>` and call
-the ``VIDIOC_ENUM_FMT`` ioctl with a pointer to this structure. Drivers
+the :ref:`VIDIOC_ENUM_FMT` ioctl with a pointer to this structure. Drivers
fill the rest of the structure or return an EINVAL error code. All
formats are enumerable by beginning at index zero and incrementing by
one until EINVAL is returned.
this applications initialize the ``tuner``, ``type`` and ``index``
fields, and zero out the ``reserved`` array of a struct
:ref:`v4l2_frequency_band <v4l2-frequency-band>` and call the
-``VIDIOC_ENUM_FREQ_BANDS`` ioctl with a pointer to this structure.
+:ref:`VIDIOC_ENUM_FREQ_BANDS` ioctl with a pointer to this structure.
This ioctl is supported if the ``V4L2_TUNER_CAP_FREQ_BANDS`` capability
of the corresponding tuner/modulator is set.
To query the attributes of an audio input applications initialize the
``index`` field and zero out the ``reserved`` array of a struct
-:ref:`v4l2_audio <v4l2-audio>` and call the ``VIDIOC_ENUMAUDIO``
+:ref:`v4l2_audio <v4l2-audio>` and call the :ref:`VIDIOC_ENUMAUDIO`
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 audio inputs applications shall begin at index
To query the attributes of a video input applications initialize the
``index`` field of struct :ref:`v4l2_input <v4l2-input>` and call the
-``VIDIOC_ENUMINPUT`` ioctl with a pointer to this structure. Drivers
+:ref:`VIDIOC_ENUMINPUT` 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 inputs applications shall begin
at index zero, incrementing by one until the driver returns EINVAL.
To query the attributes of a video outputs applications initialize the
``index`` field of struct :ref:`v4l2_output <v4l2-output>` and call
-the ``VIDIOC_ENUMOUTPUT`` ioctl with a pointer to this structure.
+the :ref:`VIDIOC_ENUMOUTPUT` 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 outputs applications
shall begin at index zero, incrementing by one until the driver returns
To query the attributes of a video standard, especially a custom (driver
defined) one, applications initialize the ``index`` field of struct
-:ref:`v4l2_standard <v4l2-standard>` and call the ``VIDIOC_ENUMSTD``
+:ref:`v4l2_standard <v4l2-standard>` and call the :ref:`VIDIOC_ENUMSTD`
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 standards applications shall begin at index
.. [1]
The supported standards may overlap and we need an unambiguous set to
- find the current standard returned by ``VIDIOC_G_STD``.
+ find the current standard returned by :ref:`VIDIOC_G_STD`.
.. [2]
Japan uses a standard similar to M/NTSC (V4L2_STD_NTSC_M_JP).
for open() for details. Currently only O_CLOEXEC, O_RDONLY, O_WRONLY,
and O_RDWR are supported. All other fields must be set to zero. In the
case of multi-planar API, every plane is exported separately using
-multiple ``VIDIOC_EXPBUF`` calls.
+multiple :ref:`VIDIOC_EXPBUF` calls.
-After calling ``VIDIOC_EXPBUF`` the ``fd`` field will be set by a
+After calling :ref:`VIDIOC_EXPBUF` the ``fd`` field will be set by a
driver. This is a DMABUF file descriptor. The application may pass it to
other DMABUF-aware devices. Refer to :ref:`DMABUF importing <dmabuf>`
for details about importing DMABUF files into V4L2 nodes. It is
To query the current audio input applications zero out the ``reserved``
array of a struct :ref:`v4l2_audio <v4l2-audio>` and call the
-``VIDIOC_G_AUDIO`` ioctl with a pointer to this structure. Drivers fill
+:ref:`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.
Audio inputs have one writable property, the audio mode. To select the
current audio input *and* change the audio mode, applications initialize
the ``index`` and ``mode`` fields, and the ``reserved`` array of a
-:c:type:`struct v4l2_audio` structure and call the ``VIDIOC_S_AUDIO``
+:c:type:`struct v4l2_audio` structure and call the :ref:`VIDIOC_S_AUDIO <VIDIOC_G_AUDIO>`
ioctl. Drivers may switch to a different audio mode if the request
cannot be satisfied. However, this is a write-only ioctl, it does not
return the actual new audio mode.
- ``mode``
- Audio mode flags set by drivers and applications (on
- ``VIDIOC_S_AUDIO`` ioctl), see :ref:`audio-mode`.
+ :ref:`VIDIOC_S_AUDIO <VIDIOC_G_AUDIO>` ioctl), see :ref:`audio-mode`.
- .. row 5
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 ``VIDIOC_G_CROP`` ioctl
+respective buffer (stream) type and call the :ref:`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.
To change the cropping rectangle applications initialize the ``type``
and struct :ref:`v4l2_rect <v4l2-rect>` substructure named ``c`` of a
-v4l2_crop structure and call the ``VIDIOC_S_CROP`` ioctl with a pointer
+v4l2_crop structure and call the :ref:`VIDIOC_S_CROP <VIDIOC_G_CROP>` ioctl with a pointer
to this structure.
Do not use the multiplanar buffer types. Use
vertical scaling factor.
Finally the driver programs the hardware with the actual cropping and
-image parameters. ``VIDIOC_S_CROP`` is a write-only ioctl, it does not
+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
-``VIDIOC_G_CROP`` and :ref:`VIDIOC_G_FMT`. When the
+:ref:`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.
When cropping is not supported then no parameters are changed and
-``VIDIOC_S_CROP`` returns the EINVAL error code.
+:ref:`VIDIOC_S_CROP <VIDIOC_G_CROP>` returns the EINVAL error code.
.. _v4l2-crop:
To get the current value of a control applications initialize the ``id``
field of a struct :c:type:`struct v4l2_control` and call the
-``VIDIOC_G_CTRL`` ioctl with a pointer to this structure. To change the
+:ref:`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
-``VIDIOC_S_CTRL`` ioctl.
+:ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` ioctl.
When the ``id`` is invalid drivers return an EINVAL error code. When the
``value`` is out of bounds drivers can choose to take the closest valid
value or return an ERANGE error code, whatever seems more appropriate.
-However, ``VIDIOC_S_CTRL`` is a write-only ioctl, it does not return the
+However, :ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` is a write-only ioctl, it does not return the
actual new value. If the ``value`` is inappropriate for the control
(e.g. if it refers to an unsupported menu index of a menu control), then
EINVAL error code is returned as well.
===========
To set DV timings for the input or output, applications use the
-``VIDIOC_S_DV_TIMINGS`` ioctl and to get the current timings,
-applications use the ``VIDIOC_G_DV_TIMINGS`` ioctl. The detailed timing
+: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
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>`
:ref:`Generic Error Codes <gen-errors>` chapter.
EINVAL
- This ioctl is not supported, or the ``VIDIOC_S_DV_TIMINGS``
+ This ioctl is not supported, or the :ref:`VIDIOC_S_DV_TIMINGS <VIDIOC_G_DV_TIMINGS>`
parameter was unsuitable.
ENODATA
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 ``VIDIOC_G_EDID``. The current EDID from block
+array and call :ref:`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
-``VIDIOC_G_EDID`` is called, then the driver will set ``blocks`` to the
+:ref:`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 ``VIDIOC_G_ENC_INDEX`` ioctl provides meta data about a compressed
+The :ref:`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 ``VIDIOC_G_ENC_INDEX`` with a
+To read the data applications must call :ref:`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 ``VIDIOC_G_ENC_INDEX`` call reads up to
+picture. A :ref:`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
-``VIDIOC_G_EXT_CTRLS`` ioctl. String controls controls must also set the
+:ref:`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.
To change the value of a set of controls applications initialize the
``id``, ``size``, ``reserved2`` and ``value/value64/string/ptr`` fields
of each struct :ref:`v4l2_ext_control <v4l2-ext-control>` and call
-the ``VIDIOC_S_EXT_CTRLS`` ioctl. The controls will only be set if *all*
+the :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` ioctl. The controls will only be set if *all*
control values are valid.
To check if a set of controls have correct values applications
initialize the ``id``, ``size``, ``reserved2`` and
``value/value64/string/ptr`` fields of each struct
:ref:`v4l2_ext_control <v4l2-ext-control>` and call the
-``VIDIOC_TRY_EXT_CTRLS`` ioctl. It is up to the driver whether wrong
+:ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` ioctl. It is up to the driver whether wrong
values are automatically adjusted to a valid value or if an error is
returned.
- 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 ``VIDIOC_G_EXT_CTRLS`` finds that this value is
+ the payload. If :ref:`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
handling controls will also accept a value of 0 here, meaning that
the controls can belong to any control class. Whether drivers
support this can be tested by setting ``ctrl_class`` to 0 and
- calling ``VIDIOC_TRY_EXT_CTRLS`` with a ``count`` of 0. If that
+ calling :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` with a ``count`` of 0. If that
succeeds, then the driver supports this feature.
- .. row 3
``error_idx-1`` were read or written correctly, and the state of
the remaining controls is undefined.
- Since ``VIDIOC_TRY_EXT_CTRLS`` does not access hardware there is
+ Since :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` does not access hardware there is
also no need to handle the validation step in this special way, so
``error_idx`` will just be set to the control that failed the
validation step instead of to ``count``. This means that if
- ``VIDIOC_S_EXT_CTRLS`` fails with ``error_idx`` set to ``count``,
- then you can call ``VIDIOC_TRY_EXT_CTRLS`` to try to discover the
+ :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 ``VIDIOC_G_EXT_CTRLS``.
+ there is no ``TRY`` equivalent for :ref:`VIDIOC_G_EXT_CTRLS`.
- .. row 6
:ref:`v4l2_ext_control <v4l2-ext-control>` ``value`` was
inappropriate (e.g. the given menu index is not supported by the
driver). This error code is also returned by the
- ``VIDIOC_S_EXT_CTRLS`` and ``VIDIOC_TRY_EXT_CTRLS`` ioctls if two or
+ :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` and :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` ioctls if two or
more control values are in conflict.
ERANGE
Description
===========
-Applications can use the ``VIDIOC_G_FBUF`` and ``VIDIOC_S_FBUF`` ioctl
+Applications can use the :ref:`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 ``VIDIOC_G_FBUF``
+To get the current parameters applications call the :ref:`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.
initialize the ``flags`` field of a struct
:c:type:`struct v4l2_framebuffer`. Since the framebuffer is
implemented on the TV card all other parameters are determined by the
-driver. When an application calls ``VIDIOC_S_FBUF`` with a pointer to
+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 ``VIDIOC_G_FBUF`` does, or it returns an error
+framebuffer parameters as :ref:`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 ``VIDIOC_S_FBUF``. Again the driver prepares for
-the overlay and returns the framebuffer parameters as ``VIDIOC_G_FBUF``
+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`
does, or it returns an error code.
For a *destructive Video Overlay* applications must additionally provide
:ref:`Generic Error Codes <gen-errors>` chapter.
EPERM
- ``VIDIOC_S_FBUF`` can only be called by a privileged user to
+ :ref:`VIDIOC_S_FBUF <VIDIOC_G_FBUF>` can only be called by a privileged user to
negotiate the parameters for a destructive overlay.
EINVAL
- The ``VIDIOC_S_FBUF`` parameters are unsuitable.
+ The :ref:`VIDIOC_S_FBUF <VIDIOC_G_FBUF>` parameters are unsuitable.
.. [1]
A physical base address may not suit all platforms. GK notes in
type. For example video capture devices use
``V4L2_BUF_TYPE_VIDEO_CAPTURE`` or
``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE``. When the application calls the
-``VIDIOC_G_FMT`` ioctl with a pointer to this structure the driver fills
+:ref:`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
For details see the documentation of the various devices types in
:ref:`devices`. Good practice is to query the current parameters
first, and to modify only those parameters not suitable for the
-application. When the application calls the ``VIDIOC_S_FMT`` ioctl with
+application. When the application calls the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl with
a pointer to a :c:type:`struct v4l2_format` structure the driver
checks and adjusts the parameters against hardware abilities. Drivers
should not return an error code unless the ``type`` field is invalid,
this is a mechanism to fathom device capabilities and to approach
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 ``VIDIOC_S_FMT`` ioctl returns
-the current format parameters as ``VIDIOC_G_FMT`` does. Very simple,
+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,
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 ``VIDIOC_G_FMT`` and ``VIDIOC_S_FMT``
+application must implement the :ref:`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 ``VIDIOC_S_FMT`` attempt. When I/O is already in
+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
return the EBUSY error code.
-The ``VIDIOC_TRY_FMT`` ioctl is equivalent to ``VIDIOC_S_FMT`` with one
+The :ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>` ioctl is equivalent to :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` with one
exception: it does not change driver state. It can also be called at any
time, never returning EBUSY. This function is provided to negotiate
parameters, to learn about hardware limitations, without disabling I/O
or possibly time consuming hardware preparations. Although strongly
recommended drivers are not required to implement this ioctl.
-The format as returned by ``VIDIOC_TRY_FMT`` must be identical to what
-``VIDIOC_S_FMT`` returns for the same input or output.
+The format as returned by :ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>` must be identical to what
+:ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` returns for the same input or output.
.. _v4l2-format:
: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
-``VIDIOC_G_FREQUENCY`` ioctl with a pointer to this structure. The
+:ref:`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
initialize the ``tuner``, ``type`` and ``frequency`` fields, and the
``reserved`` array of a struct :ref:`v4l2_frequency <v4l2-frequency>`
-and call the ``VIDIOC_S_FREQUENCY`` ioctl with a pointer to this
+and call the :ref:`VIDIOC_S_FREQUENCY <VIDIOC_G_FREQUENCY>` ioctl with a pointer to this
structure. When the requested frequency is not possible the driver
-assumes the closest possible value. However ``VIDIOC_S_FREQUENCY`` is a
+assumes the closest possible value. However :ref:`VIDIOC_S_FREQUENCY <VIDIOC_G_FREQUENCY>` is a
write-only ioctl, it does not return the actual new frequency.
===========
To query the current video input applications call the
-``VIDIOC_G_INPUT`` ioctl with a pointer to an integer where the driver
+:ref:`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 select a video input applications store the number of the desired
-input in an integer and call the ``VIDIOC_S_INPUT`` ioctl with a pointer
+input in an integer and call the :ref:`VIDIOC_S_INPUT <VIDIOC_G_INPUT>` ioctl with a pointer
to this integer. Side effects are possible. For example inputs may
support different video standards, so the driver may implicitly switch
the current standard. Because of these possible side effects
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
-``VIDIOC_G_MODULATOR`` ioctl with a pointer to this structure. Drivers
+:ref:`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
Modulators have two writable properties, an audio modulation set and the
radio frequency. To change the modulated audio subprograms, applications
initialize the ``index`` and ``txsubchans`` fields and the ``reserved``
-array and call the ``VIDIOC_S_MODULATOR`` ioctl. Drivers may choose a
+array and call the :ref:`VIDIOC_S_MODULATOR <VIDIOC_G_MODULATOR>` ioctl. Drivers may choose a
different audio modulation if the request cannot be satisfied. However
this is a write-only ioctl, it does not return the actual audio
modulation selected.
``V4L2_TUNER_SUB_MONO``, ``V4L2_TUNER_SUB_STEREO`` or
``V4L2_TUNER_SUB_SAP``. If the hardware does not support the
respective audio matrix, or the current video standard does not
- permit bilingual audio the ``VIDIOC_S_MODULATOR`` ioctl shall
+ permit bilingual audio the :ref:`VIDIOC_S_MODULATOR <VIDIOC_G_MODULATOR>` ioctl shall
return an EINVAL error code and the driver shall fall back to mono
or stereo mode.
``V4L2_TUNER_SUB_MONO`` or ``V4L2_TUNER_SUB_STEREO``. If the
hardware does not support the respective audio matrix, or the
current video standard does not permit SAP the
- ``VIDIOC_S_MODULATOR`` ioctl shall return an EINVAL error code and
+ :ref:`VIDIOC_S_MODULATOR <VIDIOC_G_MODULATOR>` ioctl shall return an EINVAL error code and
driver shall fall back to mono or stereo mode.
- .. row 6
===========
To query the current video output applications call the
-``VIDIOC_G_OUTPUT`` ioctl with a pointer to an integer where the driver
+:ref:`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
code.
To select a video output applications store the number of the desired
-output in an integer and call the ``VIDIOC_S_OUTPUT`` ioctl with a
+output in an integer and call the :ref:`VIDIOC_S_OUTPUT <VIDIOC_G_OUTPUT>` ioctl with a
pointer to this integer. Side effects are possible. For example outputs
may support different video standards, so the driver may implicitly
switch the current standard. standard. Because of these possible side
section discussing the :ref:`read() <func-read>` function.
To get and set the streaming parameters applications call the
-``VIDIOC_G_PARM`` and ``VIDIOC_S_PARM`` ioctl, respectively. They take a
+:ref:`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
-``VIDIOC_G_PRIORITY`` ioctl with a pointer to an enum v4l2_priority
+:ref:`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
-an enum v4l2_priority variable and call ``VIDIOC_S_PRIORITY`` ioctl
+an enum v4l2_priority variable and call :ref:`VIDIOC_S_PRIORITY <VIDIOC_G_PRIORITY>` ioctl
with a pointer to this variable.
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 ``VIDIOC_G_SLICED_VBI_CAP`` ioctl. The
+``reserved`` array and call the :ref:`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
-``VIDIOC_G_STD`` and ``VIDIOC_S_STD`` ioctls which take a pointer to a
-:ref:`v4l2_std_id <v4l2-std-id>` type as argument. ``VIDIOC_G_STD``
+: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`
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.
-``VIDIOC_S_STD`` accepts one or more flags, being a write-only ioctl it
-does not return the actual new standard as ``VIDIOC_G_STD`` does. When
+: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
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:`Generic Error Codes <gen-errors>` chapter.
EINVAL
- The ``VIDIOC_S_STD`` parameter was unsuitable.
+ The :ref:`VIDIOC_S_STD <VIDIOC_G_STD>` parameter was unsuitable.
ENODATA
Standard video timings are not supported for this input or output.
===========
This ioctl is part of the :ref:`video overlay <overlay>` I/O method.
-Applications call ``VIDIOC_OVERLAY`` to start or stop the overlay. It
+Applications call :ref:`VIDIOC_OVERLAY` to start or stop the overlay. It
takes a pointer to an integer which must be set to zero by the
application to stop overlay, to one to start.
Description
===========
-Applications can optionally call the ``VIDIOC_PREPARE_BUF`` ioctl to
+Applications can optionally call the :ref:`VIDIOC_PREPARE_BUF` ioctl to
pass ownership of the buffer to the driver before actually enqueuing it,
-using the ``VIDIOC_QBUF`` ioctl, and to prepare it for future I/O. Such
+using the :ref:`VIDIOC_QBUF` ioctl, and to prepare it for future I/O. Such
preparations may include cache invalidation or cleaning. Performing them
in advance saves time during the actual I/O. In case such cache
operations are not required, the application can use one of
The hardware may be able to detect the current DV timings automatically,
similar to sensing the video standard. To do so, applications call
-``VIDIOC_QUERY_DV_TIMINGS`` with a pointer to a struct
+:ref:`VIDIOC_QUERY_DV_TIMINGS` with a pointer to a struct
:ref:`v4l2_dv_timings <v4l2-dv-timings>`. Once the hardware detects
the timings, it will fill in the timings structure.
Please note that drivers shall *not* switch timings automatically if new
timings are detected. Instead, drivers should send the
``V4L2_EVENT_SOURCE_CHANGE`` event (if they support this) and expect
-that userspace will take action by calling ``VIDIOC_QUERY_DV_TIMINGS``.
+that userspace will take action by calling :ref:`VIDIOC_QUERY_DV_TIMINGS`.
The reason is that new timings usually mean different buffer sizes as
well, and you cannot change buffer sizes on the fly. In general,
applications that receive the Source Change event will have to call
-``VIDIOC_QUERY_DV_TIMINGS``, and if the detected timings are valid they
+:ref:`VIDIOC_QUERY_DV_TIMINGS`, and if the detected timings are valid they
will have to stop streaming, set the new timings, allocate new buffers
and start streaming again.
field must contain a userspace pointer to an array of struct
:ref:`v4l2_plane <v4l2-plane>` and the ``length`` field has to be set
to the number of elements in that array. After calling
-``VIDIOC_QUERYBUF`` with a pointer to this structure drivers return an
+:ref:`VIDIOC_QUERYBUF` with a pointer to this structure drivers return an
error code or fill the rest of the structure.
In the ``flags`` field the ``V4L2_BUF_FLAG_MAPPED``,
===========
The hardware may be able to detect the current video standard
-automatically. To do so, applications call ``VIDIOC_QUERYSTD`` with a
+automatically. To do so, applications call :ref:`VIDIOC_QUERYSTD` with a
pointer to a :ref:`v4l2_std_id <v4l2-std-id>` type. The driver
stores here a set of candidates, this can be a single flag or a set of
supported standards if for example the hardware can only distinguish
automatically if a new video standard is detected. Instead, drivers
should send the ``V4L2_EVENT_SOURCE_CHANGE`` event (if they support
this) and expect that userspace will take action by calling
-``VIDIOC_QUERYSTD``. The reason is that a new video standard can mean
+:ref:`VIDIOC_QUERYSTD`. The reason is that a new video standard can mean
different buffer sizes as well, and you cannot change buffer sizes on
the fly. In general, applications that receive the Source Change event
-will have to call ``VIDIOC_QUERYSTD``, and if the detected video
+will have to call :ref:`VIDIOC_QUERYSTD`, and if the detected video
standard is valid they will have to stop streaming, set the new
standard, allocate new buffers and start streaming again.
When the I/O method is not supported the ioctl returns an EINVAL error
code.
-Applications can call ``VIDIOC_REQBUFS`` again to change the number of
+Applications can call :ref:`VIDIOC_REQBUFS` again to change the number of
buffers, however this cannot succeed when any buffers are still mapped.
A ``count`` value of zero frees all buffers, after aborting or finishing
any DMA in progress, an implicit
To enumerate frame intervals applications initialize the ``index``,
``pad``, ``which``, ``code``, ``width`` and ``height`` fields of struct
:ref:`v4l2_subdev_frame_interval_enum <v4l2-subdev-frame-interval-enum>`
-and call the ``VIDIOC_SUBDEV_ENUM_FRAME_INTERVAL`` ioctl with a pointer
+and call the :ref:`VIDIOC_SUBDEV_ENUM_FRAME_INTERVAL` ioctl with a pointer
to this structure. Drivers fill the rest of the structure or return an
EINVAL error code if one of the input fields is invalid. All frame
intervals are enumerable by beginning at index zero and incrementing by
To enumerate frame sizes applications initialize the ``pad``, ``which``
, ``code`` and ``index`` fields of the struct
:ref:`v4l2_subdev_mbus_code_enum <v4l2-subdev-mbus-code-enum>` and
-call the ``VIDIOC_SUBDEV_ENUM_FRAME_SIZE`` ioctl with a pointer to the
+call the :ref:`VIDIOC_SUBDEV_ENUM_FRAME_SIZE` ioctl with a pointer to the
structure. Drivers fill the minimum and maximum frame sizes or return an
EINVAL error code if one of the input parameters is invalid.
applications initialize the ``pad``, ``which`` and ``index`` fields of
struct
:ref:`v4l2_subdev_mbus_code_enum <v4l2-subdev-mbus-code-enum>` and
-call the ``VIDIOC_SUBDEV_ENUM_MBUS_CODE`` ioctl with a pointer to this
+call the :ref:`VIDIOC_SUBDEV_ENUM_MBUS_CODE` ioctl with a pointer to this
structure. Drivers fill the rest of the structure or return an EINVAL
error code if either the ``pad`` or ``index`` are invalid. All media bus
formats are enumerable by beginning at index zero and incrementing by
projects / linux-beck.git / commitdiff