vidioc-enum-frameintervals.rst (5469B)
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SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later 2.. c:namespace:: V4L 3 4.. _VIDIOC_ENUM_FRAMEINTERVALS: 5 6******************************** 7ioctl VIDIOC_ENUM_FRAMEINTERVALS 8******************************** 9 10Name 11==== 12 13VIDIOC_ENUM_FRAMEINTERVALS - Enumerate frame intervals 14 15Synopsis 16======== 17 18.. c:macro:: VIDIOC_ENUM_FRAMEINTERVALS 19 20``int ioctl(int fd, VIDIOC_ENUM_FRAMEINTERVALS, struct v4l2_frmivalenum *argp)`` 21 22Arguments 23========= 24 25``fd`` 26 File descriptor returned by :c:func:`open()`. 27 28``argp`` 29 Pointer to struct :c:type:`v4l2_frmivalenum` 30 that contains a pixel format and size and receives a frame interval. 31 32Description 33=========== 34 35This ioctl allows applications to enumerate all frame intervals that the 36device supports for the given pixel format and frame size. 37 38The supported pixel formats and frame sizes can be obtained by using the 39:ref:`VIDIOC_ENUM_FMT` and 40:ref:`VIDIOC_ENUM_FRAMESIZES` functions. 41 42The return value and the content of the ``v4l2_frmivalenum.type`` field 43depend on the type of frame intervals the device supports. Here are the 44semantics of the function for the different cases: 45 46- **Discrete:** The function returns success if the given index value 47 (zero-based) is valid. The application should increase the index by 48 one for each call until ``EINVAL`` is returned. The 49 `v4l2_frmivalenum.type` field is set to 50 `V4L2_FRMIVAL_TYPE_DISCRETE` by the driver. Of the union only 51 the `discrete` member is valid. 52 53- **Step-wise:** The function returns success if the given index value 54 is zero and ``EINVAL`` for any other index value. The 55 ``v4l2_frmivalenum.type`` field is set to 56 ``V4L2_FRMIVAL_TYPE_STEPWISE`` by the driver. Of the union only the 57 ``stepwise`` member is valid. 58 59- **Continuous:** This is a special case of the step-wise type above. 60 The function returns success if the given index value is zero and 61 ``EINVAL`` for any other index value. The ``v4l2_frmivalenum.type`` 62 field is set to ``V4L2_FRMIVAL_TYPE_CONTINUOUS`` by the driver. Of 63 the union only the ``stepwise`` member is valid and the ``step`` 64 value is set to 1. 65 66When the application calls the function with index zero, it must check 67the ``type`` field to determine the type of frame interval enumeration 68the device supports. Only for the ``V4L2_FRMIVAL_TYPE_DISCRETE`` type 69does it make sense to increase the index value to receive more frame 70intervals. 71 72.. note:: 73 74 The order in which the frame intervals are returned has no 75 special meaning. In particular does it not say anything about potential 76 default frame intervals. 77 78Applications can assume that the enumeration data does not change 79without any interaction from the application itself. This means that the 80enumeration data is consistent if the application does not perform any 81other ioctl calls while it runs the frame interval enumeration. 82 83.. note:: 84 85 **Frame intervals and frame rates:** The V4L2 API uses frame 86 intervals instead of frame rates. Given the frame interval the frame 87 rate can be computed as follows: 88 89 :: 90 91 frame_rate = 1 / frame_interval 92 93Structs 94======= 95 96In the structs below, *IN* denotes a value that has to be filled in by 97the application, *OUT* denotes values that the driver fills in. The 98application should zero out all members except for the *IN* fields. 99 100.. c:type:: v4l2_frmival_stepwise 101 102.. flat-table:: struct v4l2_frmival_stepwise 103 :header-rows: 0 104 :stub-columns: 0 105 :widths: 1 1 2 106 107 * - struct :c:type:`v4l2_fract` 108 - ``min`` 109 - Minimum frame interval [s]. 110 * - struct :c:type:`v4l2_fract` 111 - ``max`` 112 - Maximum frame interval [s]. 113 * - struct :c:type:`v4l2_fract` 114 - ``step`` 115 - Frame interval step size [s]. 116 117 118.. c:type:: v4l2_frmivalenum 119 120.. tabularcolumns:: |p{4.9cm}|p{3.3cm}|p{9.1cm}| 121 122.. flat-table:: struct v4l2_frmivalenum 123 :header-rows: 0 124 :stub-columns: 0 125 126 * - __u32 127 - ``index`` 128 - IN: Index of the given frame interval in the enumeration. 129 * - __u32 130 - ``pixel_format`` 131 - IN: Pixel format for which the frame intervals are enumerated. 132 * - __u32 133 - ``width`` 134 - IN: Frame width for which the frame intervals are enumerated. 135 * - __u32 136 - ``height`` 137 - IN: Frame height for which the frame intervals are enumerated. 138 * - __u32 139 - ``type`` 140 - OUT: Frame interval type the device supports. 141 * - union { 142 - (anonymous) 143 - OUT: Frame interval with the given index. 144 * - struct :c:type:`v4l2_fract` 145 - ``discrete`` 146 - Frame interval [s]. 147 * - struct :c:type:`v4l2_frmival_stepwise` 148 - ``stepwise`` 149 - 150 * - } 151 - 152 - 153 * - __u32 154 - ``reserved[2]`` 155 - Reserved space for future use. Must be zeroed by drivers and 156 applications. 157 158 159Enums 160===== 161 162.. c:type:: v4l2_frmivaltypes 163 164.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.5cm}| 165 166.. flat-table:: enum v4l2_frmivaltypes 167 :header-rows: 0 168 :stub-columns: 0 169 :widths: 3 1 4 170 171 * - ``V4L2_FRMIVAL_TYPE_DISCRETE`` 172 - 1 173 - Discrete frame interval. 174 * - ``V4L2_FRMIVAL_TYPE_CONTINUOUS`` 175 - 2 176 - Continuous frame interval. 177 * - ``V4L2_FRMIVAL_TYPE_STEPWISE`` 178 - 3 179 - Step-wise defined frame interval. 180 181Return Value 182============ 183 184On success 0 is returned, on error -1 and the ``errno`` variable is set 185appropriately. The generic error codes are described at the 186:ref:`Generic Error Codes <gen-errors>` chapter.