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+.. -*- coding: utf-8; mode: rst -*-
+
+.. _VIDIOC_G_FMT:
+
+************************************************
+ioctl VIDIOC_G_FMT, VIDIOC_S_FMT, VIDIOC_TRY_FMT
+************************************************
+
+Name
+====
+
+VIDIOC_G_FMT - VIDIOC_S_FMT - VIDIOC_TRY_FMT - Get or set the data format, try a format
+
+
+Synopsis
+========
+
+.. cpp:function:: int ioctl( int fd, int request, struct v4l2_format *argp )
+
+
+Arguments
+=========
+
+``fd``
+    File descriptor returned by :ref:`open() <func-open>`.
+
+``request``
+    VIDIOC_G_FMT, VIDIOC_S_FMT, VIDIOC_TRY_FMT
+
+``argp``
+
+
+Description
+===========
+
+These ioctls are used to negotiate the format of data (typically image
+format) exchanged between driver and application.
+
+To query the current parameters applications set the ``type`` field of a
+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:`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
+:ref:`v4l2_pix_format_mplane <v4l2-pix-format-mplane>` ``pix_mp``
+member. When the requested buffer type is not supported drivers return
+an ``EINVAL`` error code.
+
+To change the current format parameters applications initialize the
+``type`` field and all fields of the respective ``fmt`` union member.
+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 :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl with
+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
+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 <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 <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
+return the ``EBUSY`` error code.
+
+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 :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:
+
+.. flat-table:: struct v4l2_format
+    :header-rows:  0
+    :stub-columns: 0
+
+
+    -  .. row 1
+
+       -  __u32
+
+       -  ``type``
+
+       -
+       -  Type of the data stream, see :ref:`v4l2-buf-type`.
+
+    -  .. row 2
+
+       -  union
+
+       -  ``fmt``
+
+    -  .. row 3
+
+       -
+       -  struct :ref:`v4l2_pix_format <v4l2-pix-format>`
+
+       -  ``pix``
+
+       -  Definition of an image format, see :ref:`pixfmt`, used by video
+	  capture and output devices.
+
+    -  .. row 4
+
+       -
+       -  struct :ref:`v4l2_pix_format_mplane <v4l2-pix-format-mplane>`
+
+       -  ``pix_mp``
+
+       -  Definition of an image format, see :ref:`pixfmt`, used by video
+	  capture and output devices that support the
+	  :ref:`multi-planar version of the API <planar-apis>`.
+
+    -  .. row 5
+
+       -
+       -  struct :ref:`v4l2_window <v4l2-window>`
+
+       -  ``win``
+
+       -  Definition of an overlaid image, see :ref:`overlay`, used by
+	  video overlay devices.
+
+    -  .. row 6
+
+       -
+       -  struct :ref:`v4l2_vbi_format <v4l2-vbi-format>`
+
+       -  ``vbi``
+
+       -  Raw VBI capture or output parameters. This is discussed in more
+	  detail in :ref:`raw-vbi`. Used by raw VBI capture and output
+	  devices.
+
+    -  .. row 7
+
+       -
+       -  struct :ref:`v4l2_sliced_vbi_format <v4l2-sliced-vbi-format>`
+
+       -  ``sliced``
+
+       -  Sliced VBI capture or output parameters. See :ref:`sliced` for
+	  details. Used by sliced VBI capture and output devices.
+
+    -  .. row 8
+
+       -
+       -  struct :ref:`v4l2_sdr_format <v4l2-sdr-format>`
+
+       -  ``sdr``
+
+       -  Definition of a data format, see :ref:`pixfmt`, used by SDR
+	  capture and output devices.
+
+    -  .. row 9
+
+       -
+       -  __u8
+
+       -  ``raw_data``\ [200]
+
+       -  Place holder for future extensions.
+
+
+Return Value
+============
+
+On success 0 is returned, on error -1 and the ``errno`` variable is set
+appropriately. The generic error codes are described at the
+:ref:`Generic Error Codes <gen-errors>` chapter.
+
+EINVAL
+    The struct :ref:`v4l2_format <v4l2-format>` ``type`` field is
+    invalid or the requested buffer type not supported.