vidioc-enum-fmt.rst 3.4 KB
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.. -*- coding: utf-8; mode: rst -*-

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.. _VIDIOC_ENUM_FMT:
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*********************
ioctl VIDIOC_ENUM_FMT
*********************

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Name
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====
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VIDIOC_ENUM_FMT - Enumerate image formats
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Synopsis
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========

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

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

``argp``


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

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

   After switching input or output the list of enumerated image
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   formats may be different.
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.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|

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

    -  .. row 1

       -  __u32

       -  ``index``

       -  Number of the format in the enumeration, set by the application.
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	  This is in no way related to the ``pixelformat`` field.
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    -  .. row 2

       -  __u32

       -  ``type``

       -  Type of the data stream, set by the application. Only these types
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	  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`` and
	  ``V4L2_BUF_TYPE_VIDEO_OVERLAY``. See :ref:`v4l2-buf-type`.
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    -  .. row 3

       -  __u32

       -  ``flags``

       -  See :ref:`fmtdesc-flags`

    -  .. row 4

       -  __u8

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       -  ``description``\ [32]
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       -  Description of the format, a NUL-terminated ASCII string. This
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	  information is intended for the user, for example: "YUV 4:2:2".
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    -  .. row 5

       -  __u32

       -  ``pixelformat``

       -  The image format identifier. This is a four character code as
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	  computed by the v4l2_fourcc() macro:
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    -  .. row 6

       -  :cspan:`2`

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	  .. _v4l2-fourcc:
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	  ``#define v4l2_fourcc(a,b,c,d)``

	  ``(((__u32)(a)<<0)|((__u32)(b)<<8)|((__u32)(c)<<16)|((__u32)(d)<<24))``
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	  Several image formats are already defined by this specification in
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	  :ref:`pixfmt`.

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	  .. attention::

	     These codes are not the same as those used
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	     in the Windows world.
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    -  .. row 7

       -  __u32

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       -  ``reserved``\ [4]
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       -  Reserved for future extensions. Drivers must set the array to
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	  zero.
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.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}|

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.. _fmtdesc-flags:

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


    -  .. row 1

       -  ``V4L2_FMT_FLAG_COMPRESSED``

       -  0x0001

       -  This is a compressed format.

    -  .. row 2

       -  ``V4L2_FMT_FLAG_EMULATED``

       -  0x0002

       -  This format is not native to the device but emulated through
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	  software (usually libv4l2), where possible try to use a native
	  format instead for better performance.
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Return Value
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============

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