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.. -*- coding: utf-8; mode: rst -*-
.. _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`` and
``V4L2_BUF_TYPE_VIDEO_OVERLAY``. 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.
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.
|
