1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later 2.. c:namespace:: V4L 3 4.. _VIDIOC_G_FMT: 5 6************************************************ 7ioctl VIDIOC_G_FMT, VIDIOC_S_FMT, VIDIOC_TRY_FMT 8************************************************ 9 10Name 11==== 12 13VIDIOC_G_FMT - VIDIOC_S_FMT - VIDIOC_TRY_FMT - Get or set the data format, try a format 14 15Synopsis 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 30Arguments 31========= 32 33``fd`` 34 File descriptor returned by :c:func:`open()`. 35 36``argp`` 37 Pointer to struct :c:type:`v4l2_format`. 38 39Description 40=========== 41 42These ioctls are used to negotiate the format of data (typically image 43format) exchanged between driver and application. 44 45To query the current parameters applications set the ``type`` field of a 46struct :c:type:`v4l2_format` to the respective buffer (stream) 47type. 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 51the respective member of the ``fmt`` union. In case of video capture 52devices that is either the struct 53:c:type:`v4l2_pix_format` ``pix`` or the struct 54:c:type:`v4l2_pix_format_mplane` ``pix_mp`` 55member. When the requested buffer type is not supported drivers return 56an ``EINVAL`` error code. 57 58To change the current format parameters applications initialize the 59``type`` field and all fields of the respective ``fmt`` union member. 60For details see the documentation of the various devices types in 61:ref:`devices`. Good practice is to query the current parameters 62first, and to modify only those parameters not suitable for the 63application. When the application calls the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl with 64a pointer to a struct :c:type:`v4l2_format` structure the driver 65checks and adjusts the parameters against hardware abilities. Drivers 66should not return an error code unless the ``type`` field is invalid, 67this is a mechanism to fathom device capabilities and to approach 68parameters acceptable for both the application and driver. On success 69the driver may program the hardware, allocate resources and generally 70prepare for data exchange. Finally the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl returns 71the current format parameters as :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` does. Very simple, 72inflexible devices may even ignore all input and always return the 73default parameters. However all V4L2 devices exchanging data with the 74application must implement the :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` and :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` 75ioctl. When the requested buffer type is not supported drivers return an 76EINVAL error code on a :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` attempt. When I/O is already in 77progress or the resource is not available for other reasons drivers 78return the ``EBUSY`` error code. 79 80The :ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>` ioctl is equivalent to :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` with one 81exception: it does not change driver state. It can also be called at any 82time, never returning ``EBUSY``. This function is provided to negotiate 83parameters, to learn about hardware limitations, without disabling I/O 84or possibly time consuming hardware preparations. Although strongly 85recommended drivers are not required to implement this ioctl. 86 87The 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{1.2cm}|p{4.6cm}|p{3.0cm}|p{8.6cm}| 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 139Return Value 140============ 141 142On success 0 is returned, on error -1 and the ``errno`` variable is set 143appropriately. The generic error codes are described at the 144:ref:`Generic Error Codes <gen-errors>` chapter. 145 146EINVAL 147 The struct :c:type:`v4l2_format` ``type`` field is 148 invalid or the requested buffer type not supported. 149 150EBUSY 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. 155