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/userspace-api/media/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 - Type of the data stream, see :c:type:`v4l2_buf_type`. 107 * - union { 108 - ``fmt`` 109 * - struct :c:type:`v4l2_pix_format` 110 - ``pix`` 111 - Definition of an image format, see :ref:`pixfmt`, used by video 112 capture and output devices. 113 * - struct :c:type:`v4l2_pix_format_mplane` 114 - ``pix_mp`` 115 - Definition of an image format, see :ref:`pixfmt`, used by video 116 capture and output devices that support the 117 :ref:`multi-planar version of the API <planar-apis>`. 118 * - struct :c:type:`v4l2_window` 119 - ``win`` 120 - Definition of an overlaid image, see :ref:`overlay`, used by 121 video overlay devices. 122 * - struct :c:type:`v4l2_vbi_format` 123 - ``vbi`` 124 - Raw VBI capture or output parameters. This is discussed in more 125 detail in :ref:`raw-vbi`. Used by raw VBI capture and output 126 devices. 127 * - struct :c:type:`v4l2_sliced_vbi_format` 128 - ``sliced`` 129 - Sliced VBI capture or output parameters. See :ref:`sliced` for 130 details. Used by sliced VBI capture and output devices. 131 * - struct :c:type:`v4l2_sdr_format` 132 - ``sdr`` 133 - Definition of a data format, see :ref:`pixfmt`, used by SDR 134 capture and output devices. 135 * - struct :c:type:`v4l2_meta_format` 136 - ``meta`` 137 - Definition of a metadata format, see :ref:`meta-formats`, used by 138 metadata capture devices. 139 * - __u8 140 - ``raw_data``\ [200] 141 - Place holder for future extensions. 142 * - } 143 - 144 145 146Return Value 147============ 148 149On success 0 is returned, on error -1 and the ``errno`` variable is set 150appropriately. The generic error codes are described at the 151:ref:`Generic Error Codes <gen-errors>` chapter. 152 153EINVAL 154 The struct :c:type:`v4l2_format` ``type`` field is 155 invalid or the requested buffer type not supported. 156 157EBUSY 158 The device is busy and cannot change the format. This could be 159 because or the device is streaming or buffers are allocated or 160 queued to the driver. Relevant for :ref:`VIDIOC_S_FMT 161 <VIDIOC_G_FMT>` only. 162