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+.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
+.. c:namespace:: V4L
+
+.. _VIDIOC_ENUM_FMT:
+
+*********************
+ioctl VIDIOC_ENUM_FMT
+*********************
+
+Name
+====
+
+VIDIOC_ENUM_FMT - Enumerate image formats
+
+Synopsis
+========
+
+.. c:macro:: VIDIOC_ENUM_FMT
+
+``int ioctl(int fd, VIDIOC_ENUM_FMT, struct v4l2_fmtdesc *argp)``
+
+Arguments
+=========
+
+``fd``
+ File descriptor returned by :c:func:`open()`.
+
+``argp``
+ Pointer to struct :c:type:`v4l2_fmtdesc`.
+
+Description
+===========
+
+To enumerate image formats applications initialize the ``type``, ``mbus_code``
+and ``index`` fields 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. If applicable, drivers shall return
+formats in preference order, where preferred formats are returned before
+(that is, with lower ``index`` value) less-preferred formats.
+
+Depending on the ``V4L2_CAP_IO_MC`` :ref:`capability <device-capabilities>`,
+the ``mbus_code`` field is handled differently:
+
+1) ``V4L2_CAP_IO_MC`` is not set (also known as a 'video-node-centric' driver)
+
+ Applications shall initialize the ``mbus_code`` field to zero and drivers
+ shall ignore the value of the field.
+
+ Drivers shall enumerate all image formats.
+
+ .. note::
+
+ After switching the input or output the list of enumerated image
+ formats may be different.
+
+2) ``V4L2_CAP_IO_MC`` is set (also known as an 'MC-centric' driver)
+
+ If the ``mbus_code`` field is zero, then all image formats
+ shall be enumerated.
+
+ If the ``mbus_code`` field is initialized to a valid (non-zero)
+ :ref:`media bus format code <v4l2-mbus-pixelcode>`, then drivers
+ shall restrict enumeration to only the image formats that can produce
+ (for video output devices) or be produced from (for video capture
+ devices) that media bus code. If the ``mbus_code`` is unsupported by
+ the driver, then ``EINVAL`` shall be returned.
+
+ Regardless of the value of the ``mbus_code`` field, the enumerated image
+ formats shall not depend on the active configuration of the video device
+ or device pipeline.
+
+.. 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``,
+ ``V4L2_BUF_TYPE_META_CAPTURE`` and
+ ``V4L2_BUF_TYPE_META_OUTPUT``.
+ 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
+ - ``mbus_code``
+ - Media bus code restricting the enumerated formats, set by the
+ application. Only applicable to drivers that advertise the
+ ``V4L2_CAP_IO_MC`` :ref:`capability <device-capabilities>`, shall be 0
+ otherwise.
+ * - __u32
+ - ``reserved``\ [3]
+ - 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. This flag is valid for stateful codecs only.
+ * - ``V4L2_FMT_FLAG_ENC_CAP_FRAME_INTERVAL``
+ - 0x0010
+ - The hardware encoder supports setting the ``CAPTURE`` coded frame
+ interval separately from the ``OUTPUT`` raw frame interval.
+ Setting the ``OUTPUT`` raw frame interval with :ref:`VIDIOC_S_PARM <VIDIOC_G_PARM>`
+ also sets the ``CAPTURE`` coded frame interval to the same value.
+ If this flag is set, then the ``CAPTURE`` coded frame interval can be
+ set to a different value afterwards. This is typically used for
+ offline encoding where the ``OUTPUT`` raw frame interval is used as
+ a hint for reserving hardware encoder resources and the ``CAPTURE`` coded
+ frame interval is the actual frame rate embedded in the encoded video
+ stream.
+
+ 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 encoders only.
+ * - ``V4L2_FMT_FLAG_CSC_COLORSPACE``
+ - 0x0020
+ - The driver allows the application to try to change the default
+ colorspace. This flag is relevant only for capture devices.
+ The application can ask to configure the colorspace of the capture device
+ when calling the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl with
+ :ref:`V4L2_PIX_FMT_FLAG_SET_CSC <v4l2-pix-fmt-flag-set-csc>` set.
+ * - ``V4L2_FMT_FLAG_CSC_XFER_FUNC``
+ - 0x0040
+ - The driver allows the application to try to change the default
+ transfer function. This flag is relevant only for capture devices.
+ The application can ask to configure the transfer function of the capture
+ device when calling the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl with
+ :ref:`V4L2_PIX_FMT_FLAG_SET_CSC <v4l2-pix-fmt-flag-set-csc>` set.
+ * - ``V4L2_FMT_FLAG_CSC_YCBCR_ENC``
+ - 0x0080
+ - The driver allows the application to try to change the default
+ Y'CbCr encoding. This flag is relevant only for capture devices.
+ The application can ask to configure the Y'CbCr encoding of the capture device
+ when calling the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl with
+ :ref:`V4L2_PIX_FMT_FLAG_SET_CSC <v4l2-pix-fmt-flag-set-csc>` set.
+ * - ``V4L2_FMT_FLAG_CSC_HSV_ENC``
+ - 0x0080
+ - The driver allows the application to try to change the default
+ HSV encoding. This flag is relevant only for capture devices.
+ The application can ask to configure the HSV encoding of the capture device
+ when calling the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl with
+ :ref:`V4L2_PIX_FMT_FLAG_SET_CSC <v4l2-pix-fmt-flag-set-csc>` set.
+ * - ``V4L2_FMT_FLAG_CSC_QUANTIZATION``
+ - 0x0100
+ - The driver allows the application to try to change the default
+ quantization. This flag is relevant only for capture devices.
+ The application can ask to configure the quantization of the capture
+ device when calling the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl with
+ :ref:`V4L2_PIX_FMT_FLAG_SET_CSC <v4l2-pix-fmt-flag-set-csc>` set.
+
+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.
+
+ If ``V4L2_CAP_IO_MC`` is set and the specified ``mbus_code``
+ is unsupported, then also return this error code.