planes, while the buffer structure acts as a container for the planes.
Only pointers to buffers (planes) are exchanged, the data itself is not
copied. These pointers, together with meta-information like timestamps
-or field parity, are stored in a struct :c:type:`struct v4l2_buffer`,
+or field parity, are stored in a struct :ref:`struct v4l2_buffer <v4l2-buffer>`,
argument to the :ref:`VIDIOC_QUERYBUF`,
:ref:`VIDIOC_QBUF` and
:ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl. In the multi-planar API,
-some plane-specific members of struct :c:type:`struct v4l2_buffer`,
+some plane-specific members of struct :ref:`struct v4l2_buffer <v4l2-buffer>`,
such as pointers and sizes for each plane, are stored in struct
-:c:type:`struct v4l2_plane` instead. In that case, struct
-:c:type:`struct v4l2_buffer` contains an array of plane structures.
+:ref:`struct v4l2_plane <v4l2-plane>` instead. In that case, struct
+:ref:`struct v4l2_buffer <v4l2-buffer>` contains an array of plane structures.
Dequeued video buffers come with timestamps. The driver decides at which
part of the frame and with which clock the timestamp is taken. Please
- When using the multi-planar API, contains a userspace pointer to
an array of struct :ref:`v4l2_plane <v4l2-plane>`. The size of
the array should be put in the ``length`` field of this
- :c:type:`struct v4l2_buffer` structure.
+ :ref:`struct v4l2_buffer <v4l2-buffer>` structure.
- .. row 15
Timecodes
=========
-The :c:type:`struct v4l2_timecode` structure is designed to hold a
+The :ref:`struct v4l2_timecode <v4l2-timecode>` structure is designed to hold a
:ref:`smpte12m` or similar timecode. (struct
:c:type:`struct timeval` timestamps are stored in struct
:ref:`v4l2_buffer <v4l2-buffer>` field ``timestamp``.)
:ref:`v4l2_format <v4l2-format>` to
``V4L2_BUF_TYPE_VIDEO_OUTPUT_OVERLAY`` and call the
:ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` ioctl. The driver fills the
-:c:type:`struct v4l2_window` substructure named ``win``. It is not
+:ref:`struct v4l2_window <v4l2-window>` substructure named ``win``. It is not
possible to retrieve a previously programmed clipping list or bitmap.
To program the source rectangle 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 <VIDIOC_G_FMT>` ioctl. The driver fills the
-:c:type:`struct v4l2_window` substructure named ``win``. It is not
+:ref:`struct v4l2_window <v4l2-window>` substructure named ``win``. It is not
possible to retrieve a previously programmed clipping list or bitmap.
To program the overlay window applications set the ``type`` field of a
Applications can request different parameters by initializing or
modifying the ``fmt.sliced`` member and calling the
:ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl with a pointer to the
-:c:type:`struct v4l2_format` structure.
+:ref:`struct v4l2_format <v4l2-format>` structure.
The sliced VBI API is more complicated than the raw VBI API because the
hardware must be told which VBI service to expect on each scan line. Not
A single :ref:`read() <func-read>` or :ref:`write() <func-write>`
call must pass all data belonging to one video frame. That is an array
-of :c:type:`struct v4l2_sliced_vbi_data` structures with one or
+of :ref:`struct v4l2_sliced_vbi_data <v4l2-sliced-vbi-data>` structures with one or
more elements and a total size not exceeding ``io_size`` bytes. Likewise
in streaming I/O mode one buffer of ``io_size`` bytes must contain data
of one video frame. The ``id`` of unused
-:c:type:`struct v4l2_sliced_vbi_data` elements must be zero.
+:ref:`struct v4l2_sliced_vbi_data <v4l2-sliced-vbi-data>` elements must be zero.
.. _v4l2-sliced-vbi-data:
The control array is a struct
:ref:`v4l2_ext_control <v4l2-ext-control>` array. The
-:c:type:`struct v4l2_ext_control` structure is very similar to
+:ref:`struct v4l2_ext_control <v4l2-ext-control>` structure is very similar to
struct :ref:`v4l2_control <v4l2-control>`, except for the fact that
it also allows for 64-bit values and pointers to be passed.
On success :c:func:`poll()` returns the number of file descriptors
that have been selected (that is, file descriptors for which the
-``revents`` field of the respective :c:type:`struct pollfd` structure
+``revents`` field of the respective :c:func:`struct pollfd` structure
is non-zero). Capture devices set the ``POLLIN`` and ``POLLRDNORM``
flags in the ``revents`` field, output devices the ``POLLOUT`` and
``POLLWRNORM`` flags. When the function timed out it returns a value of
the outgoing queue of the driver the function returns immediately.
On success :c:func:`select()` returns the total number of bits set in
-the :c:type:`struct fd_set`s. When the function timed out it returns
+:c:func:`struct fd_set`. When the function timed out it returns
a value of zero. On failure it returns -1 and the ``errno`` variable is
set appropriately. When the application did not call
:ref:`VIDIOC_QBUF` or
- ``priv``
- This field indicates whether the remaining fields of the
- :c:type:`struct v4l2_pix_format` structure, also called the
+ :ref:`struct v4l2_pix_format <v4l2-pix-format>` structure, also called the
extended fields, are valid. When set to
``V4L2_PIX_FMT_PRIV_MAGIC``, it indicates that the extended fields
have been correctly initialized. When set to any other value it
To use the extended fields, applications must set the ``priv``
field to ``V4L2_PIX_FMT_PRIV_MAGIC``, initialize all the extended
fields and zero the unused bytes of the
- :c:type:`struct v4l2_format` ``raw_data`` field.
+ :ref:`struct v4l2_format <v4l2-format>` ``raw_data`` field.
When the ``priv`` field isn't set to ``V4L2_PIX_FMT_PRIV_MAGIC``
drivers must act as if all the extended fields were set to zero.
Multi-planar format structures
******************************
-The :c:type:`struct v4l2_plane_pix_format` structures define size
+The :ref:`struct v4l2_plane_pix_format <v4l2-plane-pix-format>` structures define size
and layout for each of the planes in a multi-planar format. The
-:c:type:`struct v4l2_pix_format_mplane` structure contains
+:ref:`struct v4l2_pix_format_mplane <v4l2-pix-format-mplane>` structure contains
information common to all planes (such as image width and height) and an
-array of :c:type:`struct v4l2_plane_pix_format` structures,
+array of :ref:`struct v4l2_plane_pix_format <v4l2-plane-pix-format>` structures,
describing all planes of that format.
Image Formats
#############
The V4L2 API was primarily designed for devices exchanging image data
-with applications. The :c:type:`struct v4l2_pix_format` and
-:c:type:`struct v4l2_pix_format_mplane` structures define the
+with applications. The :ref:`struct v4l2_pix_format <v4l2-pix-format>` and
+:ref:`struct v4l2_pix_format_mplane <v4l2-pix-format-mplane>` structures define the
format and layout of an image in memory. The former is used with the
single-planar API, while the latter is used with the multi-planar
version (see :ref:`planar-apis`). Image formats are negotiated with
create buffers of different sizes.
To allocate the device buffers applications must initialize the relevant
-fields of the :c:type:`struct v4l2_create_buffers` structure. The
+fields of the :ref:`struct v4l2_create_buffers <v4l2-create-buffers>` structure. The
``count`` field must be set to the number of requested buffers, the
``memory`` field specifies the requested I/O method and the ``reserved``
array must be zeroed.
set as custom standards. Multiple bits can be set if the hardware
does not distinguish between these standards, however separate
indices do not indicate the opposite. The ``id`` must be unique.
- No other enumerated :c:type:`struct v4l2_standard` structure,
+ No other enumerated :ref:`struct v4l2_standard <v4l2-standard>` structure,
for this input or output anyway, can contain the same set of bits.
- .. row 3
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 :ref:`VIDIOC_S_AUDIO <VIDIOC_G_AUDIO>`
+:ref:`struct v4l2_audio <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.
Audio outputs have no writable properties. Nevertheless, to select the
current audio output applications can initialize the ``index`` field and
``reserved`` array (which in the future may contain writable properties)
-of a :c:type:`struct v4l2_audioout` structure and call the
+of a :ref:`struct v4l2_audioout <v4l2-audioout>` structure and call the
``VIDIOC_S_AUDOUT`` ioctl. Drivers switch to the requested output or
return the ``EINVAL`` error code when the index is out of bounds. This is a
write-only ioctl, it does not return the current audio output attributes
===========
To query the cropping rectangle size and position applications set the
-``type`` field of a :c:type:`struct v4l2_crop` structure to the
+``type`` field of a :ref:`struct v4l2_crop <v4l2-crop>` structure to the
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.
===========
To get the current value of a control applications initialize the ``id``
-field of a struct :c:type:`struct v4l2_control` and call the
+field of a struct :ref:`struct v4l2_control <v4l2-control>` and call 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
+fields of a struct :ref:`struct v4l2_control <v4l2-control>` and call the
:ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` ioctl.
When the ``id`` is invalid drivers return an ``EINVAL`` error code. When the
always non-destructive.
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`
+ioctl with a pointer to a :ref:`struct v4l2_framebuffer <v4l2-framebuffer>`
structure. The driver fills all fields of the structure or returns an
EINVAL error code when overlays are not supported.
To set the parameters for a *Video Output Overlay*, applications must
initialize the ``flags`` field of a struct
-:c:type:`struct v4l2_framebuffer`. Since the framebuffer is
+:ref:`struct v4l2_framebuffer <v4l2-framebuffer>`. Since the framebuffer is
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
format) exchanged between driver and application.
To query the current parameters applications set the ``type`` field of a
-struct :c:type:`struct v4l2_format` to the respective buffer (stream)
+struct :ref:`struct v4l2_format <v4l2-format>` to the respective buffer (stream)
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:`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 :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl with
-a pointer to a :c:type:`struct v4l2_format` structure the driver
+a pointer to a :ref:`struct v4l2_format <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
To get and set the streaming parameters applications call the
: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
+pointer to a struct :ref:`struct v4l2_streamparm <v4l2-streamparm>` which contains a
union holding separate parameters for input and output devices.
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:`struct v4l2_standard <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 <VIDIOC_G_STD>` does. When
received audio programs do not match.
Currently this is the only field of struct
- :c:type:`struct v4l2_tuner` applications can change.
+ :ref:`struct v4l2_tuner <v4l2-tuner>` applications can change.
- .. row 15
``V4L2_BUF_FLAG_NO_CACHE_INVALIDATE`` and
``V4L2_BUF_FLAG_NO_CACHE_CLEAN`` flags to skip the respective step.
-The :c:type:`struct v4l2_buffer` structure is specified in
+The :ref:`struct v4l2_buffer <v4l2-buffer>` structure is specified in
:ref:`buffer`.
range from zero to the number of buffers allocated with
:ref:`VIDIOC_REQBUFS` (struct
:ref:`v4l2_requestbuffers <v4l2-requestbuffers>` ``count``) minus
-one. The contents of the struct :c:type:`struct v4l2_buffer` returned
+one. The contents of the struct :ref:`struct v4l2_buffer <v4l2-buffer>` returned
by a :ref:`VIDIOC_QUERYBUF` ioctl will do as well.
When the buffer is intended for output (``type`` is
``V4L2_BUF_TYPE_VIDEO_OUTPUT``, ``V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE``,
:ref:`open() <func-open>` function, ``VIDIOC_DQBUF`` returns
immediately with an ``EAGAIN`` error code when no buffer is available.
-The :c:type:`struct v4l2_buffer` structure is specified in
+The :ref:`struct v4l2_buffer <v4l2-buffer>` structure is specified in
:ref:`buffer`.
array elements. The driver may or may not set the remaining fields and
flags, they are meaningless in this context.
-The :c:type:`struct v4l2_buffer` structure is specified in
+The :ref:`struct v4l2_buffer <v4l2-buffer>` structure is specified in
:ref:`buffer`.
allocation.
To allocate device buffers applications initialize all fields of the
-:c:type:`struct v4l2_requestbuffers` structure. They set the ``type``
+:ref:`struct v4l2_requestbuffers <v4l2-requestbuffers>` structure. They set the ``type``
field to the respective stream or buffer type, the ``count`` field to
the desired number of buffers, ``memory`` must be set to the requested
I/O method and the ``reserved`` array must be zeroed. When the ioctl is
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