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_ENUM_FRAMEINTERVALS:
11
12********************************
13ioctl VIDIOC_ENUM_FRAMEINTERVALS
14********************************
15
16Name
17====
18
19VIDIOC_ENUM_FRAMEINTERVALS - Enumerate frame intervals
20
21
22Synopsis
23========
24
25.. c:function:: int ioctl( int fd, VIDIOC_ENUM_FRAMEINTERVALS, struct v4l2_frmivalenum *argp )
26    :name: VIDIOC_ENUM_FRAMEINTERVALS
27
28
29Arguments
30=========
31
32``fd``
33    File descriptor returned by :ref:`open() <func-open>`.
34
35``argp``
36    Pointer to struct :c:type:`v4l2_frmivalenum`
37    that contains a pixel format and size and receives a frame interval.
38
39
40Description
41===========
42
43This ioctl allows applications to enumerate all frame intervals that the
44device supports for the given pixel format and frame size.
45
46The supported pixel formats and frame sizes can be obtained by using the
47:ref:`VIDIOC_ENUM_FMT` and
48:ref:`VIDIOC_ENUM_FRAMESIZES` functions.
49
50The return value and the content of the ``v4l2_frmivalenum.type`` field
51depend on the type of frame intervals the device supports. Here are the
52semantics of the function for the different cases:
53
54-  **Discrete:** The function returns success if the given index value
55   (zero-based) is valid. The application should increase the index by
56   one for each call until ``EINVAL`` is returned. The
57   `v4l2_frmivalenum.type` field is set to
58   `V4L2_FRMIVAL_TYPE_DISCRETE` by the driver. Of the union only
59   the `discrete` member is valid.
60
61-  **Step-wise:** The function returns success if the given index value
62   is zero and ``EINVAL`` for any other index value. The
63   ``v4l2_frmivalenum.type`` field is set to
64   ``V4L2_FRMIVAL_TYPE_STEPWISE`` by the driver. Of the union only the
65   ``stepwise`` member is valid.
66
67-  **Continuous:** This is a special case of the step-wise type above.
68   The function returns success if the given index value is zero and
69   ``EINVAL`` for any other index value. The ``v4l2_frmivalenum.type``
70   field is set to ``V4L2_FRMIVAL_TYPE_CONTINUOUS`` by the driver. Of
71   the union only the ``stepwise`` member is valid and the ``step``
72   value is set to 1.
73
74When the application calls the function with index zero, it must check
75the ``type`` field to determine the type of frame interval enumeration
76the device supports. Only for the ``V4L2_FRMIVAL_TYPE_DISCRETE`` type
77does it make sense to increase the index value to receive more frame
78intervals.
79
80.. note::
81
82   The order in which the frame intervals are returned has no
83   special meaning. In particular does it not say anything about potential
84   default frame intervals.
85
86Applications can assume that the enumeration data does not change
87without any interaction from the application itself. This means that the
88enumeration data is consistent if the application does not perform any
89other ioctl calls while it runs the frame interval enumeration.
90
91.. note::
92
93   **Frame intervals and frame rates:** The V4L2 API uses frame
94   intervals instead of frame rates. Given the frame interval the frame
95   rate can be computed as follows:
96
97   ::
98
99       frame_rate = 1 / frame_interval
100
101
102Structs
103=======
104
105In the structs below, *IN* denotes a value that has to be filled in by
106the application, *OUT* denotes values that the driver fills in. The
107application should zero out all members except for the *IN* fields.
108
109
110.. c:type:: v4l2_frmival_stepwise
111
112.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
113
114.. flat-table:: struct v4l2_frmival_stepwise
115    :header-rows:  0
116    :stub-columns: 0
117    :widths:       1 1 2
118
119    * - struct :c:type:`v4l2_fract`
120      - ``min``
121      - Minimum frame interval [s].
122    * - struct :c:type:`v4l2_fract`
123      - ``max``
124      - Maximum frame interval [s].
125    * - struct :c:type:`v4l2_fract`
126      - ``step``
127      - Frame interval step size [s].
128
129
130
131.. c:type:: v4l2_frmivalenum
132
133.. tabularcolumns:: |p{1.8cm}|p{4.4cm}|p{2.4cm}|p{8.9cm}|
134
135.. flat-table:: struct v4l2_frmivalenum
136    :header-rows:  0
137    :stub-columns: 0
138
139    * - __u32
140      - ``index``
141      -
142      - IN: Index of the given frame interval in the enumeration.
143    * - __u32
144      - ``pixel_format``
145      -
146      - IN: Pixel format for which the frame intervals are enumerated.
147    * - __u32
148      - ``width``
149      -
150      - IN: Frame width for which the frame intervals are enumerated.
151    * - __u32
152      - ``height``
153      -
154      - IN: Frame height for which the frame intervals are enumerated.
155    * - __u32
156      - ``type``
157      -
158      - OUT: Frame interval type the device supports.
159    * - union
160      -
161      -
162      - OUT: Frame interval with the given index.
163    * -
164      - struct :c:type:`v4l2_fract`
165      - ``discrete``
166      - Frame interval [s].
167    * -
168      - struct :c:type:`v4l2_frmival_stepwise`
169      - ``stepwise``
170      -
171    * - __u32
172      - ``reserved[2]``
173      -
174      - Reserved space for future use. Must be zeroed by drivers and
175	applications.
176
177
178
179Enums
180=====
181
182
183.. c:type:: v4l2_frmivaltypes
184
185.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}|
186
187.. flat-table:: enum v4l2_frmivaltypes
188    :header-rows:  0
189    :stub-columns: 0
190    :widths:       3 1 4
191
192    * - ``V4L2_FRMIVAL_TYPE_DISCRETE``
193      - 1
194      - Discrete frame interval.
195    * - ``V4L2_FRMIVAL_TYPE_CONTINUOUS``
196      - 2
197      - Continuous frame interval.
198    * - ``V4L2_FRMIVAL_TYPE_STEPWISE``
199      - 3
200      - Step-wise defined frame interval.
201
202
203Return Value
204============
205
206On success 0 is returned, on error -1 and the ``errno`` variable is set
207appropriately. The generic error codes are described at the
208:ref:`Generic Error Codes <gen-errors>` chapter.
209