linux/linux-5.4.31/Documentation/media/uapi/v4l/vidioc-enum-fmt.rst

.. Permission is granted to copy, distribute and/or modify this
.. document under the terms of the GNU Free Documentation License,
.. Version 1.1 or any later version published by the Free Software
.. Foundation, with no Invariant Sections, no Front-Cover Texts
.. and no Back-Cover Texts. A copy of the license is included at
.. Documentation/media/uapi/fdl-appendix.rst.
..
.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections

.. _VIDIOC_ENUM_FMT:

*********************
ioctl VIDIOC_ENUM_FMT
*********************

Name
====

VIDIOC_ENUM_FMT - Enumerate image formats


Synopsis
========

.. c:function:: int ioctl( int fd, VIDIOC_ENUM_FMT, struct v4l2_fmtdesc *argp )
    :name: VIDIOC_ENUM_FMT


Arguments
=========

``fd``
    File descriptor returned by :ref:`open() <func-open>`.

``argp``
    Pointer to struct :c:type:`v4l2_fmtdesc`.


Description
===========

To enumerate image formats applications initialize the ``type`` and
``index`` field of struct :c:type:`v4l2_fmtdesc` and call
the :ref:`VIDIOC_ENUM_FMT` ioctl with a pointer to this structure. Drivers
fill the rest of the structure or return an ``EINVAL`` error code. All
formats are enumerable by beginning at index zero and incrementing by
one until ``EINVAL`` is returned.

.. note::

   After switching input or output the list of enumerated image
   formats may be different.


.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|

.. c:type:: v4l2_fmtdesc

.. flat-table:: struct v4l2_fmtdesc
    :header-rows:  0
    :stub-columns: 0
    :widths:       1 1 2

    * - __u32
      - ``index``
      - Number of the format in the enumeration, set by the application.
	This is in no way related to the ``pixelformat`` field.
    * - __u32
      - ``type``
      - Type of the data stream, set by the application. Only these types
	are valid here: ``V4L2_BUF_TYPE_VIDEO_CAPTURE``,
	``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE``,
	``V4L2_BUF_TYPE_VIDEO_OUTPUT``,
	``V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE``,
	``V4L2_BUF_TYPE_VIDEO_OVERLAY``,
	``V4L2_BUF_TYPE_SDR_CAPTURE``,
	``V4L2_BUF_TYPE_SDR_OUTPUT`` and
	``V4L2_BUF_TYPE_META_CAPTURE``.
	See :c:type:`v4l2_buf_type`.
    * - __u32
      - ``flags``
      - See :ref:`fmtdesc-flags`
    * - __u8
      - ``description``\ [32]
      - Description of the format, a NUL-terminated ASCII string. This
	information is intended for the user, for example: "YUV 4:2:2".
    * - __u32
      - ``pixelformat``
      - The image format identifier. This is a four character code as
	computed by the v4l2_fourcc() macro:
    * - :cspan:`2`

	.. _v4l2-fourcc:

	``#define v4l2_fourcc(a,b,c,d)``

	``(((__u32)(a)<<0)|((__u32)(b)<<8)|((__u32)(c)<<16)|((__u32)(d)<<24))``

	Several image formats are already defined by this specification in
	:ref:`pixfmt`.

	.. attention::

	   These codes are not the same as those used
	   in the Windows world.
    * - __u32
      - ``reserved``\ [4]
      - Reserved for future extensions. Drivers must set the array to
	zero.



.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}|

.. _fmtdesc-flags:

.. flat-table:: Image Format Description Flags
    :header-rows:  0
    :stub-columns: 0
    :widths:       3 1 4

    * - ``V4L2_FMT_FLAG_COMPRESSED``
      - 0x0001
      - This is a compressed format.
    * - ``V4L2_FMT_FLAG_EMULATED``
      - 0x0002
      - This format is not native to the device but emulated through
	software (usually libv4l2), where possible try to use a native
	format instead for better performance.
    * - ``V4L2_FMT_FLAG_CONTINUOUS_BYTESTREAM``
      - 0x0004
      - The hardware decoder for this compressed bytestream format (aka coded
	format) is capable of parsing a continuous bytestream. Applications do
	not need to parse the bytestream themselves to find the boundaries
	between frames/fields. This flag can only be used in combination with
	the ``V4L2_FMT_FLAG_COMPRESSED`` flag, since this applies to compressed
	formats only. This flag is valid for stateful decoders only.
    * - ``V4L2_FMT_FLAG_DYN_RESOLUTION``
      - 0x0008
      - Dynamic resolution switching is supported by the device for this
	compressed bytestream format (aka coded format). It will notify the user
	via the event ``V4L2_EVENT_SOURCE_CHANGE`` when changes in the video
	parameters are detected. This flag can only be used in combination
	with the ``V4L2_FMT_FLAG_COMPRESSED`` flag, since this applies to
	compressed formats only. It is also only applies to stateful codecs.


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.

EINVAL
    The struct :c:type:`v4l2_fmtdesc` ``type`` is not
    supported or the ``index`` is out of bounds.