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243 lines
8.8 KiB
243 lines
8.8 KiB
.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later |
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.. c:namespace:: V4L |
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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:macro:: VIDIOC_ENUM_FMT |
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``int ioctl(int fd, VIDIOC_ENUM_FMT, struct v4l2_fmtdesc *argp)`` |
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Arguments |
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========= |
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``fd`` |
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File descriptor returned by :c:func:`open()`. |
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``argp`` |
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Pointer to struct :c:type:`v4l2_fmtdesc`. |
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Description |
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=========== |
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To enumerate image formats applications initialize the ``type``, ``mbus_code`` |
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and ``index`` fields 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. If applicable, drivers shall return |
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formats in preference order, where preferred formats are returned before |
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(that is, with lower ``index`` value) less-preferred formats. |
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Depending on the ``V4L2_CAP_IO_MC`` :ref:`capability <device-capabilities>`, |
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the ``mbus_code`` field is handled differently: |
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1) ``V4L2_CAP_IO_MC`` is not set (also known as a 'video-node-centric' driver) |
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Applications shall initialize the ``mbus_code`` field to zero and drivers |
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shall ignore the value of the field. |
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Drivers shall enumerate all image formats. |
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.. note:: |
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After switching the input or output the list of enumerated image |
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formats may be different. |
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2) ``V4L2_CAP_IO_MC`` is set (also known as an 'MC-centric' driver) |
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If the ``mbus_code`` field is zero, then all image formats |
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shall be enumerated. |
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If the ``mbus_code`` field is initialized to a valid (non-zero) |
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:ref:`media bus format code <v4l2-mbus-pixelcode>`, then drivers |
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shall restrict enumeration to only the image formats that can produce |
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(for video output devices) or be produced from (for video capture |
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devices) that media bus code. If the ``mbus_code`` is unsupported by |
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the driver, then ``EINVAL`` shall be returned. |
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Regardless of the value of the ``mbus_code`` field, the enumerated image |
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formats shall not depend on the active configuration of the video device |
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or device pipeline. |
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.. c:type:: v4l2_fmtdesc |
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.. cssclass:: longtable |
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.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm}| |
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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``, |
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``V4L2_BUF_TYPE_VIDEO_OVERLAY``, |
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``V4L2_BUF_TYPE_SDR_CAPTURE``, |
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``V4L2_BUF_TYPE_SDR_OUTPUT``, |
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``V4L2_BUF_TYPE_META_CAPTURE`` and |
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``V4L2_BUF_TYPE_META_OUTPUT``. |
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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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- ``mbus_code`` |
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- Media bus code restricting the enumerated formats, set by the |
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application. Only applicable to drivers that advertise the |
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``V4L2_CAP_IO_MC`` :ref:`capability <device-capabilities>`, shall be 0 |
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otherwise. |
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* - __u32 |
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- ``reserved``\ [3] |
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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{8.4cm}|p{1.8cm}|p{7.1cm}| |
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.. cssclass:: longtable |
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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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* - ``V4L2_FMT_FLAG_CONTINUOUS_BYTESTREAM`` |
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- 0x0004 |
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- The hardware decoder for this compressed bytestream format (aka coded |
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format) is capable of parsing a continuous bytestream. Applications do |
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not need to parse the bytestream themselves to find the boundaries |
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between frames/fields. |
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This flag can only be used in combination with the |
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``V4L2_FMT_FLAG_COMPRESSED`` flag, since this applies to compressed |
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formats only. This flag is valid for stateful decoders only. |
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* - ``V4L2_FMT_FLAG_DYN_RESOLUTION`` |
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- 0x0008 |
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- Dynamic resolution switching is supported by the device for this |
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compressed bytestream format (aka coded format). It will notify the user |
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via the event ``V4L2_EVENT_SOURCE_CHANGE`` when changes in the video |
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parameters are detected. |
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This flag can only be used in combination with the |
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``V4L2_FMT_FLAG_COMPRESSED`` flag, since this applies to |
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compressed formats only. This flag is valid for stateful codecs only. |
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* - ``V4L2_FMT_FLAG_ENC_CAP_FRAME_INTERVAL`` |
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- 0x0010 |
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- The hardware encoder supports setting the ``CAPTURE`` coded frame |
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interval separately from the ``OUTPUT`` raw frame interval. |
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Setting the ``OUTPUT`` raw frame interval with :ref:`VIDIOC_S_PARM <VIDIOC_G_PARM>` |
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also sets the ``CAPTURE`` coded frame interval to the same value. |
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If this flag is set, then the ``CAPTURE`` coded frame interval can be |
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set to a different value afterwards. This is typically used for |
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offline encoding where the ``OUTPUT`` raw frame interval is used as |
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a hint for reserving hardware encoder resources and the ``CAPTURE`` coded |
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frame interval is the actual frame rate embedded in the encoded video |
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stream. |
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This flag can only be used in combination with the |
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``V4L2_FMT_FLAG_COMPRESSED`` flag, since this applies to |
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compressed formats only. This flag is valid for stateful encoders only. |
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* - ``V4L2_FMT_FLAG_CSC_COLORSPACE`` |
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- 0x0020 |
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- The driver allows the application to try to change the default |
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colorspace. This flag is relevant only for capture devices. |
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The application can ask to configure the colorspace of the capture device |
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when calling the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl with |
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:ref:`V4L2_PIX_FMT_FLAG_SET_CSC <v4l2-pix-fmt-flag-set-csc>` set. |
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* - ``V4L2_FMT_FLAG_CSC_XFER_FUNC`` |
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- 0x0040 |
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- The driver allows the application to try to change the default |
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transfer function. This flag is relevant only for capture devices. |
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The application can ask to configure the transfer function of the capture |
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device when calling the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl with |
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:ref:`V4L2_PIX_FMT_FLAG_SET_CSC <v4l2-pix-fmt-flag-set-csc>` set. |
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* - ``V4L2_FMT_FLAG_CSC_YCBCR_ENC`` |
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- 0x0080 |
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- The driver allows the application to try to change the default |
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Y'CbCr encoding. This flag is relevant only for capture devices. |
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The application can ask to configure the Y'CbCr encoding of the capture device |
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when calling the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl with |
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:ref:`V4L2_PIX_FMT_FLAG_SET_CSC <v4l2-pix-fmt-flag-set-csc>` set. |
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* - ``V4L2_FMT_FLAG_CSC_HSV_ENC`` |
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- 0x0080 |
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- The driver allows the application to try to change the default |
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HSV encoding. This flag is relevant only for capture devices. |
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The application can ask to configure the HSV encoding of the capture device |
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when calling the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl with |
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:ref:`V4L2_PIX_FMT_FLAG_SET_CSC <v4l2-pix-fmt-flag-set-csc>` set. |
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* - ``V4L2_FMT_FLAG_CSC_QUANTIZATION`` |
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- 0x0100 |
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- The driver allows the application to try to change the default |
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quantization. This flag is relevant only for capture devices. |
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The application can ask to configure the quantization of the capture |
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device when calling the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl with |
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:ref:`V4L2_PIX_FMT_FLAG_SET_CSC <v4l2-pix-fmt-flag-set-csc>` set. |
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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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If ``V4L2_CAP_IO_MC`` is set and the specified ``mbus_code`` |
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is unsupported, then also return this error code.
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