1 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
2 .. c:namespace:: V4L
3
4 .. _VIDIOC_G_FMT:
5
6 ************************************************
7 ioctl VIDIOC_G_FMT, VIDIOC_S_FMT, VIDIOC_TRY_FMT
8 ************************************************
9
10 Name
11 ====
12
13 VIDIOC_G_FMT - VIDIOC_S_FMT - VIDIOC_TRY_FMT - Get or set the data format, try a format
14
15 Synopsis
16 ========
17
18 .. c:macro:: VIDIOC_G_FMT
19
20 ``int ioctl(int fd, VIDIOC_G_FMT, struct v4l2_format *argp)``
21
22 .. c:macro:: VIDIOC_S_FMT
23
24 ``int ioctl(int fd, VIDIOC_S_FMT, struct v4l2_format *argp)``
25
26 .. c:macro:: VIDIOC_TRY_FMT
27
28 ``int ioctl(int fd, VIDIOC_TRY_FMT, struct v4l2_format *argp)``
29
30 Arguments
31 =========
32
33 ``fd``
34 File descriptor returned by :c:func:`open()`.
35
36 ``argp``
37 Pointer to struct :c:type:`v4l2_format`.
38
39 Description
40 ===========
41
42 These ioctls are used to negotiate the format of data (typically image
43 format) exchanged between driver and application.
44
45 To query the current parameters applications set the ``type`` field of a
46 struct :c:type:`v4l2_format` to the respective buffer (stream)
47 type. For example video capture devices use
48 ``V4L2_BUF_TYPE_VIDEO_CAPTURE`` or
49 ``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE``. When the application calls the
50 :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` ioctl with a pointer to this structure the driver fills
51 the respective member of the ``fmt`` union. In case of video capture
52 devices that is either the struct
53 :c:type:`v4l2_pix_format` ``pix`` or the struct
54 :c:type:`v4l2_pix_format_mplane` ``pix_mp``
55 member. When the requested buffer type is not supported drivers return
56 an ``EINVAL`` error code.
57
58 To change the current format parameters applications initialize the
59 ``type`` field and all fields of the respective ``fmt`` union member.
60 For details see the documentation of the various devices types in
61 :ref:`devices`. Good practice is to query the current parameters
62 first, and to modify only those parameters not suitable for the
63 application. When the application calls the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl with
64 a pointer to a struct :c:type:`v4l2_format` structure the driver
65 checks and adjusts the parameters against hardware abilities. Drivers
66 should not return an error code unless the ``type`` field is invalid,
67 this is a mechanism to fathom device capabilities and to approach
68 parameters acceptable for both the application and driver. On success
69 the driver may program the hardware, allocate resources and generally
70 prepare for data exchange. Finally the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl returns
71 the current format parameters as :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` does. Very simple,
72 inflexible devices may even ignore all input and always return the
73 default parameters. However all V4L2 devices exchanging data with the
74 application must implement the :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` and :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>`
75 ioctl. When the requested buffer type is not supported drivers return an
76 EINVAL error code on a :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` attempt. When I/O is already in
77 progress or the resource is not available for other reasons drivers
78 return the ``EBUSY`` error code.
79
80 The :ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>` ioctl is equivalent to :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` with one
81 exception: it does not change driver state. It can also be called at any
82 time, never returning ``EBUSY``. This function is provided to negotiate
83 parameters, to learn about hardware limitations, without disabling I/O
84 or possibly time consuming hardware preparations. Although strongly
85 recommended drivers are not required to implement this ioctl.
86
87 The format as returned by :ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>` must be identical to what
88 :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` returns for the same input or output.
89
90 .. c:type:: v4l2_format
91
92 .. tabularcolumns:: |p{7.4cm}|p{4.4cm}|p{5.5cm}|
93
94 .. flat-table:: struct v4l2_format
95 :header-rows: 0
96 :stub-columns: 0
97
98 * - __u32
99 - ``type``
100 - Type of the data stream, see :c:type:`v4l2_buf_type`.
101 * - union {
102 - ``fmt``
103 * - struct :c:type:`v4l2_pix_format`
104 - ``pix``
105 - Definition of an image format, see :ref:`pixfmt`, used by video
106 capture and output devices.
107 * - struct :c:type:`v4l2_pix_format_mplane`
108 - ``pix_mp``
109 - Definition of an image format, see :ref:`pixfmt`, used by video
110 capture and output devices that support the
111 :ref:`multi-planar version of the API <planar-apis>`.
112 * - struct :c:type:`v4l2_window`
113 - ``win``
114 - Definition of an overlaid image, see :ref:`overlay`, used by
115 video overlay devices.
116 * - struct :c:type:`v4l2_vbi_format`
117 - ``vbi``
118 - Raw VBI capture or output parameters. This is discussed in more
119 detail in :ref:`raw-vbi`. Used by raw VBI capture and output
120 devices.
121 * - struct :c:type:`v4l2_sliced_vbi_format`
122 - ``sliced``
123 - Sliced VBI capture or output parameters. See :ref:`sliced` for
124 details. Used by sliced VBI capture and output devices.
125 * - struct :c:type:`v4l2_sdr_format`
126 - ``sdr``
127 - Definition of a data format, see :ref:`pixfmt`, used by SDR
128 capture and output devices.
129 * - struct :c:type:`v4l2_meta_format`
130 - ``meta``
131 - Definition of a metadata format, see :ref:`meta-formats`, used by
132 metadata capture devices.
133 * - __u8
134 - ``raw_data``\ [200]
135 - Place holder for future extensions.
136 * - }
137 -
138
139 Return Value
140 ============
141
142 On success 0 is returned, on error -1 and the ``errno`` variable is set
143 appropriately. The generic error codes are described at the
144 :ref:`Generic Error Codes <gen-errors>` chapter.
145
146 EINVAL
147 The struct :c:type:`v4l2_format` ``type`` field is
148 invalid or the requested buffer type not supported.
149
150 EBUSY
151 The device is busy and cannot change the format. This could be
152 because or the device is streaming or buffers are allocated or
153 queued to the driver. Relevant for :ref:`VIDIOC_S_FMT
154 <VIDIOC_G_FMT>` only.
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