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:

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.
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.

.. c:type:: v4l2_fmtdesc

.. cssclass:: longtable

.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm}|

.. 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{8.4cm}|p{1.8cm}|p{7.1cm}|

.. cssclass:: longtable

.. _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.
* - ``V4L2_FMT_FLAG_META_LINE_BASED``
  - 0x0200
  - The metadata format is line-based. In this case the ``width``,
``height`` and ``bytesperline`` fields of :c:type:`v4l2_meta_format` are
valid. The buffer consists of ``height`` lines, each having ``width``
Data Units of data and the offset (in bytes) between the beginning of
each two consecutive lines is ``bytesperline``.

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.