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+.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
+.. c:namespace:: V4L
+
+.. _VIDIOC_ENUM_FRAMEINTERVALS:
+
+********************************
+ioctl VIDIOC_ENUM_FRAMEINTERVALS
+********************************
+
+Name
+====
+
+VIDIOC_ENUM_FRAMEINTERVALS - Enumerate frame intervals
+
+Synopsis
+========
+
+.. c:macro:: VIDIOC_ENUM_FRAMEINTERVALS
+
+``int ioctl(int fd, VIDIOC_ENUM_FRAMEINTERVALS, struct v4l2_frmivalenum *argp)``
+
+Arguments
+=========
+
+``fd``
+ File descriptor returned by :c:func:`open()`.
+
+``argp``
+ Pointer to struct :c:type:`v4l2_frmivalenum`
+ that contains a pixel format and size and receives a frame interval.
+
+Description
+===========
+
+This ioctl allows applications to enumerate all frame intervals that the
+device supports for the given pixel format and frame size.
+
+The supported pixel formats and frame sizes can be obtained by using the
+:ref:`VIDIOC_ENUM_FMT` and
+:ref:`VIDIOC_ENUM_FRAMESIZES` functions.
+
+The return value and the content of the ``v4l2_frmivalenum.type`` field
+depend on the type of frame intervals the device supports. Here are the
+semantics of the function for the different cases:
+
+- **Discrete:** The function returns success if the given index value
+ (zero-based) is valid. The application should increase the index by
+ one for each call until ``EINVAL`` is returned. The
+ `v4l2_frmivalenum.type` field is set to
+ `V4L2_FRMIVAL_TYPE_DISCRETE` by the driver. Of the union only
+ the `discrete` member is valid.
+
+- **Step-wise:** The function returns success if the given index value
+ is zero and ``EINVAL`` for any other index value. The
+ ``v4l2_frmivalenum.type`` field is set to
+ ``V4L2_FRMIVAL_TYPE_STEPWISE`` by the driver. Of the union only the
+ ``stepwise`` member is valid.
+
+- **Continuous:** This is a special case of the step-wise type above.
+ The function returns success if the given index value is zero and
+ ``EINVAL`` for any other index value. The ``v4l2_frmivalenum.type``
+ field is set to ``V4L2_FRMIVAL_TYPE_CONTINUOUS`` by the driver. Of
+ the union only the ``stepwise`` member is valid and the ``step``
+ value is set to 1.
+
+When the application calls the function with index zero, it must check
+the ``type`` field to determine the type of frame interval enumeration
+the device supports. Only for the ``V4L2_FRMIVAL_TYPE_DISCRETE`` type
+does it make sense to increase the index value to receive more frame
+intervals.
+
+.. note::
+
+ The order in which the frame intervals are returned has no
+ special meaning. In particular does it not say anything about potential
+ default frame intervals.
+
+Applications can assume that the enumeration data does not change
+without any interaction from the application itself. This means that the
+enumeration data is consistent if the application does not perform any
+other ioctl calls while it runs the frame interval enumeration.
+
+.. note::
+
+ **Frame intervals and frame rates:** The V4L2 API uses frame
+ intervals instead of frame rates. Given the frame interval the frame
+ rate can be computed as follows:
+
+ ::
+
+ frame_rate = 1 / frame_interval
+
+Structs
+=======
+
+In the structs below, *IN* denotes a value that has to be filled in by
+the application, *OUT* denotes values that the driver fills in. The
+application should zero out all members except for the *IN* fields.
+
+.. c:type:: v4l2_frmival_stepwise
+
+.. flat-table:: struct v4l2_frmival_stepwise
+ :header-rows: 0
+ :stub-columns: 0
+ :widths: 1 1 2
+
+ * - struct :c:type:`v4l2_fract`
+ - ``min``
+ - Minimum frame interval [s].
+ * - struct :c:type:`v4l2_fract`
+ - ``max``
+ - Maximum frame interval [s].
+ * - struct :c:type:`v4l2_fract`
+ - ``step``
+ - Frame interval step size [s].
+
+
+.. c:type:: v4l2_frmivalenum
+
+.. tabularcolumns:: |p{4.9cm}|p{3.3cm}|p{9.1cm}|
+
+.. flat-table:: struct v4l2_frmivalenum
+ :header-rows: 0
+ :stub-columns: 0
+
+ * - __u32
+ - ``index``
+ - IN: Index of the given frame interval in the enumeration.
+ * - __u32
+ - ``pixel_format``
+ - IN: Pixel format for which the frame intervals are enumerated.
+ * - __u32
+ - ``width``
+ - IN: Frame width for which the frame intervals are enumerated.
+ * - __u32
+ - ``height``
+ - IN: Frame height for which the frame intervals are enumerated.
+ * - __u32
+ - ``type``
+ - OUT: Frame interval type the device supports.
+ * - union {
+ - (anonymous)
+ - OUT: Frame interval with the given index.
+ * - struct :c:type:`v4l2_fract`
+ - ``discrete``
+ - Frame interval [s].
+ * - struct :c:type:`v4l2_frmival_stepwise`
+ - ``stepwise``
+ -
+ * - }
+ -
+ -
+ * - __u32
+ - ``reserved[2]``
+ - Reserved space for future use. Must be zeroed by drivers and
+ applications.
+
+
+Enums
+=====
+
+.. c:type:: v4l2_frmivaltypes
+
+.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.5cm}|
+
+.. flat-table:: enum v4l2_frmivaltypes
+ :header-rows: 0
+ :stub-columns: 0
+ :widths: 3 1 4
+
+ * - ``V4L2_FRMIVAL_TYPE_DISCRETE``
+ - 1
+ - Discrete frame interval.
+ * - ``V4L2_FRMIVAL_TYPE_CONTINUOUS``
+ - 2
+ - Continuous frame interval.
+ * - ``V4L2_FRMIVAL_TYPE_STEPWISE``
+ - 3
+ - Step-wise defined frame interval.
+
+Return Value
+============
+
+On success 0 is returned, on error -1 and the ``errno`` variable is set
+appropriately. The generic error codes are described at the
+:ref:`Generic Error Codes <gen-errors>` chapter.