1.. Permission is granted to copy, distribute and/or modify this
2.. document under the terms of the GNU Free Documentation License,
3.. Version 1.1 or any later version published by the Free Software
4.. Foundation, with no Invariant Sections, no Front-Cover Texts
5.. and no Back-Cover Texts. A copy of the license is included at
6.. Documentation/media/uapi/fdl-appendix.rst.
7..
8.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections
9
10.. _VIDIOC_G_FMT:
11
12************************************************
13ioctl VIDIOC_G_FMT, VIDIOC_S_FMT, VIDIOC_TRY_FMT
14************************************************
15
16Name
17====
18
19VIDIOC_G_FMT - VIDIOC_S_FMT - VIDIOC_TRY_FMT - Get or set the data format, try a format
20
21
22Synopsis
23========
24
25.. c:function:: int ioctl( int fd, VIDIOC_G_FMT, struct v4l2_format *argp )
26    :name: VIDIOC_G_FMT
27
28.. c:function:: int ioctl( int fd, VIDIOC_S_FMT, struct v4l2_format *argp )
29    :name: VIDIOC_S_FMT
30
31.. c:function:: int ioctl( int fd, VIDIOC_TRY_FMT, struct v4l2_format *argp )
32    :name: VIDIOC_TRY_FMT
33
34Arguments
35=========
36
37``fd``
38    File descriptor returned by :ref:`open() <func-open>`.
39
40``argp``
41    Pointer to struct :c:type:`v4l2_format`.
42
43
44Description
45===========
46
47These ioctls are used to negotiate the format of data (typically image
48format) exchanged between driver and application.
49
50To query the current parameters applications set the ``type`` field of a
51struct :c:type:`v4l2_format` to the respective buffer (stream)
52type. For example video capture devices use
53``V4L2_BUF_TYPE_VIDEO_CAPTURE`` or
54``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE``. When the application calls the
55:ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` ioctl with a pointer to this structure the driver fills
56the respective member of the ``fmt`` union. In case of video capture
57devices that is either the struct
58:c:type:`v4l2_pix_format` ``pix`` or the struct
59:c:type:`v4l2_pix_format_mplane` ``pix_mp``
60member. When the requested buffer type is not supported drivers return
61an ``EINVAL`` error code.
62
63To change the current format parameters applications initialize the
64``type`` field and all fields of the respective ``fmt`` union member.
65For details see the documentation of the various devices types in
66:ref:`devices`. Good practice is to query the current parameters
67first, and to modify only those parameters not suitable for the
68application. When the application calls the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl with
69a pointer to a struct :c:type:`v4l2_format` structure the driver
70checks and adjusts the parameters against hardware abilities. Drivers
71should not return an error code unless the ``type`` field is invalid,
72this is a mechanism to fathom device capabilities and to approach
73parameters acceptable for both the application and driver. On success
74the driver may program the hardware, allocate resources and generally
75prepare for data exchange. Finally the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl returns
76the current format parameters as :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` does. Very simple,
77inflexible devices may even ignore all input and always return the
78default parameters. However all V4L2 devices exchanging data with the
79application must implement the :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` and :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>`
80ioctl. When the requested buffer type is not supported drivers return an
81EINVAL error code on a :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` attempt. When I/O is already in
82progress or the resource is not available for other reasons drivers
83return the ``EBUSY`` error code.
84
85The :ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>` ioctl is equivalent to :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` with one
86exception: it does not change driver state. It can also be called at any
87time, never returning ``EBUSY``. This function is provided to negotiate
88parameters, to learn about hardware limitations, without disabling I/O
89or possibly time consuming hardware preparations. Although strongly
90recommended drivers are not required to implement this ioctl.
91
92The format as returned by :ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>` must be identical to what
93:ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` returns for the same input or output.
94
95
96.. c:type:: v4l2_format
97
98.. tabularcolumns::  |p{1.2cm}|p{4.6cm}|p{3.0cm}|p{8.6cm}|
99
100.. flat-table:: struct v4l2_format
101    :header-rows:  0
102    :stub-columns: 0
103
104    * - __u32
105      - ``type``
106      -
107      - Type of the data stream, see :c:type:`v4l2_buf_type`.
108    * - union
109      - ``fmt``
110    * -
111      - struct :c:type:`v4l2_pix_format`
112      - ``pix``
113      - Definition of an image format, see :ref:`pixfmt`, used by video
114	capture and output devices.
115    * -
116      - struct :c:type:`v4l2_pix_format_mplane`
117      - ``pix_mp``
118      - Definition of an image format, see :ref:`pixfmt`, used by video
119	capture and output devices that support the
120	:ref:`multi-planar version of the API <planar-apis>`.
121    * -
122      - struct :c:type:`v4l2_window`
123      - ``win``
124      - Definition of an overlaid image, see :ref:`overlay`, used by
125	video overlay devices.
126    * -
127      - struct :c:type:`v4l2_vbi_format`
128      - ``vbi``
129      - Raw VBI capture or output parameters. This is discussed in more
130	detail in :ref:`raw-vbi`. Used by raw VBI capture and output
131	devices.
132    * -
133      - struct :c:type:`v4l2_sliced_vbi_format`
134      - ``sliced``
135      - Sliced VBI capture or output parameters. See :ref:`sliced` for
136	details. Used by sliced VBI capture and output devices.
137    * -
138      - struct :c:type:`v4l2_sdr_format`
139      - ``sdr``
140      - Definition of a data format, see :ref:`pixfmt`, used by SDR
141	capture and output devices.
142    * -
143      - struct :c:type:`v4l2_meta_format`
144      - ``meta``
145      - Definition of a metadata format, see :ref:`meta-formats`, used by
146	metadata capture devices.
147    * -
148      - __u8
149      - ``raw_data``\ [200]
150      - Place holder for future extensions.
151
152
153Return Value
154============
155
156On success 0 is returned, on error -1 and the ``errno`` variable is set
157appropriately. The generic error codes are described at the
158:ref:`Generic Error Codes <gen-errors>` chapter.
159
160EINVAL
161    The struct :c:type:`v4l2_format` ``type`` field is
162    invalid or the requested buffer type not supported.
163
164EBUSY
165    The device is busy and cannot change the format. This could be
166    because or the device is streaming or buffers are allocated or
167    queued to the driver. Relevant for :ref:`VIDIOC_S_FMT
168    <VIDIOC_G_FMT>` only.
169