0001 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
0002 .. c:namespace:: V4L
0003
0004 .. _VIDIOC_G_FMT:
0005
0006 ************************************************
0007 ioctl VIDIOC_G_FMT, VIDIOC_S_FMT, VIDIOC_TRY_FMT
0008 ************************************************
0009
0010 Name
0011 ====
0012
0013 VIDIOC_G_FMT - VIDIOC_S_FMT - VIDIOC_TRY_FMT - Get or set the data format, try a format
0014
0015 Synopsis
0016 ========
0017
0018 .. c:macro:: VIDIOC_G_FMT
0019
0020 ``int ioctl(int fd, VIDIOC_G_FMT, struct v4l2_format *argp)``
0021
0022 .. c:macro:: VIDIOC_S_FMT
0023
0024 ``int ioctl(int fd, VIDIOC_S_FMT, struct v4l2_format *argp)``
0025
0026 .. c:macro:: VIDIOC_TRY_FMT
0027
0028 ``int ioctl(int fd, VIDIOC_TRY_FMT, struct v4l2_format *argp)``
0029
0030 Arguments
0031 =========
0032
0033 ``fd``
0034 File descriptor returned by :c:func:`open()`.
0035
0036 ``argp``
0037 Pointer to struct :c:type:`v4l2_format`.
0038
0039 Description
0040 ===========
0041
0042 These ioctls are used to negotiate the format of data (typically image
0043 format) exchanged between driver and application.
0044
0045 To query the current parameters applications set the ``type`` field of a
0046 struct :c:type:`v4l2_format` to the respective buffer (stream)
0047 type. For example video capture devices use
0048 ``V4L2_BUF_TYPE_VIDEO_CAPTURE`` or
0049 ``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE``. When the application calls the
0050 :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` ioctl with a pointer to this structure the driver fills
0051 the respective member of the ``fmt`` union. In case of video capture
0052 devices that is either the struct
0053 :c:type:`v4l2_pix_format` ``pix`` or the struct
0054 :c:type:`v4l2_pix_format_mplane` ``pix_mp``
0055 member. When the requested buffer type is not supported drivers return
0056 an ``EINVAL`` error code.
0057
0058 To change the current format parameters applications initialize the
0059 ``type`` field and all fields of the respective ``fmt`` union member.
0060 For details see the documentation of the various devices types in
0061 :ref:`devices`. Good practice is to query the current parameters
0062 first, and to modify only those parameters not suitable for the
0063 application. When the application calls the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl with
0064 a pointer to a struct :c:type:`v4l2_format` structure the driver
0065 checks and adjusts the parameters against hardware abilities. Drivers
0066 should not return an error code unless the ``type`` field is invalid,
0067 this is a mechanism to fathom device capabilities and to approach
0068 parameters acceptable for both the application and driver. On success
0069 the driver may program the hardware, allocate resources and generally
0070 prepare for data exchange. Finally the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl returns
0071 the current format parameters as :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` does. Very simple,
0072 inflexible devices may even ignore all input and always return the
0073 default parameters. However all V4L2 devices exchanging data with the
0074 application must implement the :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` and :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>`
0075 ioctl. When the requested buffer type is not supported drivers return an
0076 EINVAL error code on a :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` attempt. When I/O is already in
0077 progress or the resource is not available for other reasons drivers
0078 return the ``EBUSY`` error code.
0079
0080 The :ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>` ioctl is equivalent to :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` with one
0081 exception: it does not change driver state. It can also be called at any
0082 time, never returning ``EBUSY``. This function is provided to negotiate
0083 parameters, to learn about hardware limitations, without disabling I/O
0084 or possibly time consuming hardware preparations. Although strongly
0085 recommended drivers are not required to implement this ioctl.
0086
0087 The format as returned by :ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>` must be identical to what
0088 :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` returns for the same input or output.
0089
0090 .. c:type:: v4l2_format
0091
0092 .. tabularcolumns:: |p{7.4cm}|p{4.4cm}|p{5.5cm}|
0093
0094 .. flat-table:: struct v4l2_format
0095 :header-rows: 0
0096 :stub-columns: 0
0097
0098 * - __u32
0099 - ``type``
0100 - Type of the data stream, see :c:type:`v4l2_buf_type`.
0101 * - union {
0102 - ``fmt``
0103 * - struct :c:type:`v4l2_pix_format`
0104 - ``pix``
0105 - Definition of an image format, see :ref:`pixfmt`, used by video
0106 capture and output devices.
0107 * - struct :c:type:`v4l2_pix_format_mplane`
0108 - ``pix_mp``
0109 - Definition of an image format, see :ref:`pixfmt`, used by video
0110 capture and output devices that support the
0111 :ref:`multi-planar version of the API <planar-apis>`.
0112 * - struct :c:type:`v4l2_window`
0113 - ``win``
0114 - Definition of an overlaid image, see :ref:`overlay`, used by
0115 video overlay devices.
0116 * - struct :c:type:`v4l2_vbi_format`
0117 - ``vbi``
0118 - Raw VBI capture or output parameters. This is discussed in more
0119 detail in :ref:`raw-vbi`. Used by raw VBI capture and output
0120 devices.
0121 * - struct :c:type:`v4l2_sliced_vbi_format`
0122 - ``sliced``
0123 - Sliced VBI capture or output parameters. See :ref:`sliced` for
0124 details. Used by sliced VBI capture and output devices.
0125 * - struct :c:type:`v4l2_sdr_format`
0126 - ``sdr``
0127 - Definition of a data format, see :ref:`pixfmt`, used by SDR
0128 capture and output devices.
0129 * - struct :c:type:`v4l2_meta_format`
0130 - ``meta``
0131 - Definition of a metadata format, see :ref:`meta-formats`, used by
0132 metadata capture devices.
0133 * - __u8
0134 - ``raw_data``\ [200]
0135 - Place holder for future extensions.
0136 * - }
0137 -
0138
0139 Return Value
0140 ============
0141
0142 On success 0 is returned, on error -1 and the ``errno`` variable is set
0143 appropriately. The generic error codes are described at the
0144 :ref:`Generic Error Codes <gen-errors>` chapter.
0145
0146 EINVAL
0147 The struct :c:type:`v4l2_format` ``type`` field is
0148 invalid or the requested buffer type not supported.
0149
0150 EBUSY
0151 The device is busy and cannot change the format. This could be
0152 because or the device is streaming or buffers are allocated or
0153 queued to the driver. Relevant for :ref:`VIDIOC_S_FMT
0154 <VIDIOC_G_FMT>` only.
