mirror of https://gitee.com/openkylin/linux.git
130 lines
3.2 KiB
ReStructuredText
130 lines
3.2 KiB
ReStructuredText
.. -*- coding: utf-8; mode: rst -*-
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.. _VIDIOC_ENUM_FMT:
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*********************
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ioctl VIDIOC_ENUM_FMT
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*********************
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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 )
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:name: VIDIOC_ENUM_FMT
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Arguments
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=========
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``fd``
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File descriptor returned by :ref:`open() <func-open>`.
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``argp``
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Description
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===========
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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::
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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
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:header-rows: 0
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:stub-columns: 0
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:widths: 1 1 2
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* - __u32
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- ``index``
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- 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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* - __u32
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- ``type``
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- Type of the data stream, set by the application. Only these types
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are valid here: ``V4L2_BUF_TYPE_VIDEO_CAPTURE``,
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``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE``,
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``V4L2_BUF_TYPE_VIDEO_OUTPUT``,
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``V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE`` and
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``V4L2_BUF_TYPE_VIDEO_OVERLAY``. See :c:type:`v4l2_buf_type`.
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* - __u32
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- ``flags``
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- See :ref:`fmtdesc-flags`
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* - __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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* - __u32
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- ``pixelformat``
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- 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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* - :cspan:`2`
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.. _v4l2-fourcc:
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``#define v4l2_fourcc(a,b,c,d)``
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``(((__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::
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These codes are not the same as those used
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in the Windows world.
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* - __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
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:header-rows: 0
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:stub-columns: 0
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:widths: 3 1 4
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* - ``V4L2_FMT_FLAG_COMPRESSED``
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- 0x0001
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- This is a compressed format.
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* - ``V4L2_FMT_FLAG_EMULATED``
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- 0x0002
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- 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
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format instead for better performance.
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Return Value
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============
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On success 0 is returned, on error -1 and the ``errno`` variable is set
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appropriately. The generic error codes are described at the
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:ref:`Generic Error Codes <gen-errors>` chapter.
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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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