134 lines
5.6 KiB
ReStructuredText
134 lines
5.6 KiB
ReStructuredText
.. -*- coding: utf-8; mode: rst -*-
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******************************
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Single-planar format structure
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******************************
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.. tabularcolumns:: |p{4.0cm}|p{2.5cm}|p{11.0cm}|
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.. c:type:: v4l2_pix_format
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.. cssclass:: longtable
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.. flat-table:: struct v4l2_pix_format
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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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- ``width``
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- Image width in pixels.
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* - __u32
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- ``height``
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- Image height in pixels. If ``field`` is one of ``V4L2_FIELD_TOP``,
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``V4L2_FIELD_BOTTOM`` or ``V4L2_FIELD_ALTERNATE`` then height
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refers to the number of lines in the field, otherwise it refers to
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the number of lines in the frame (which is twice the field height
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for interlaced formats).
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* - :cspan:`2` Applications set these fields to request an image
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size, drivers return the closest possible values. In case of
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planar formats the ``width`` and ``height`` applies to the largest
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plane. To avoid ambiguities drivers must return values rounded up
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to a multiple of the scale factor of any smaller planes. For
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example when the image format is YUV 4:2:0, ``width`` and
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``height`` must be multiples of two.
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* - __u32
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- ``pixelformat``
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- The pixel format or type of compression, set by the application.
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This is a little endian
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:ref:`four character code <v4l2-fourcc>`. V4L2 defines standard
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RGB formats in :ref:`rgb-formats`, YUV formats in
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:ref:`yuv-formats`, and reserved codes in
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:ref:`reserved-formats`
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* - enum :c:type::`v4l2_field`
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- ``field``
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- Video images are typically interlaced. Applications can request to
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capture or output only the top or bottom field, or both fields
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interlaced or sequentially stored in one buffer or alternating in
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separate buffers. Drivers return the actual field order selected.
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For more details on fields see :ref:`field-order`.
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* - __u32
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- ``bytesperline``
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- Distance in bytes between the leftmost pixels in two adjacent
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lines.
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* - :cspan:`2`
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Both applications and drivers can set this field to request
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padding bytes at the end of each line. Drivers however may ignore
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the value requested by the application, returning ``width`` times
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bytes per pixel or a larger value required by the hardware. That
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implies applications can just set this field to zero to get a
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reasonable default.
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Video hardware may access padding bytes, therefore they must
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reside in accessible memory. Consider cases where padding bytes
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after the last line of an image cross a system page boundary.
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Input devices may write padding bytes, the value is undefined.
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Output devices ignore the contents of padding bytes.
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When the image format is planar the ``bytesperline`` value applies
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to the first plane and is divided by the same factor as the
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``width`` field for the other planes. For example the Cb and Cr
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planes of a YUV 4:2:0 image have half as many padding bytes
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following each line as the Y plane. To avoid ambiguities drivers
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must return a ``bytesperline`` value rounded up to a multiple of
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the scale factor.
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For compressed formats the ``bytesperline`` value makes no sense.
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Applications and drivers must set this to 0 in that case.
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* - __u32
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- ``sizeimage``
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- Size in bytes of the buffer to hold a complete image, set by the
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driver. Usually this is ``bytesperline`` times ``height``. When
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the image consists of variable length compressed data this is the
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maximum number of bytes required to hold an image.
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* - enum :c:type:`v4l2_colorspace`
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- ``colorspace``
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- This information supplements the ``pixelformat`` and must be set
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by the driver for capture streams and by the application for
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output streams, see :ref:`colorspaces`.
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* - __u32
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- ``priv``
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- This field indicates whether the remaining fields of the
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struct :c:type:`v4l2_pix_format`, also called the
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extended fields, are valid. When set to
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``V4L2_PIX_FMT_PRIV_MAGIC``, it indicates that the extended fields
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have been correctly initialized. When set to any other value it
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indicates that the extended fields contain undefined values.
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Applications that wish to use the pixel format extended fields
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must first ensure that the feature is supported by querying the
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device for the :ref:`V4L2_CAP_EXT_PIX_FORMAT <querycap>`
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capability. If the capability isn't set the pixel format extended
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fields are not supported and using the extended fields will lead
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to undefined results.
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To use the extended fields, applications must set the ``priv``
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field to ``V4L2_PIX_FMT_PRIV_MAGIC``, initialize all the extended
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fields and zero the unused bytes of the
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struct :c:type:`v4l2_format` ``raw_data`` field.
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When the ``priv`` field isn't set to ``V4L2_PIX_FMT_PRIV_MAGIC``
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drivers must act as if all the extended fields were set to zero.
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On return drivers must set the ``priv`` field to
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``V4L2_PIX_FMT_PRIV_MAGIC`` and all the extended fields to
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applicable values.
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* - __u32
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- ``flags``
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- Flags set by the application or driver, see :ref:`format-flags`.
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* - enum :c:type:`v4l2_ycbcr_encoding`
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- ``ycbcr_enc``
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- This information supplements the ``colorspace`` and must be set by
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the driver for capture streams and by the application for output
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streams, see :ref:`colorspaces`.
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* - enum :c:type:`v4l2_quantization`
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- ``quantization``
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- This information supplements the ``colorspace`` and must be set by
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the driver for capture streams and by the application for output
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streams, see :ref:`colorspaces`.
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* - enum :c:type:`v4l2_xfer_func`
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- ``xfer_func``
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- This information supplements the ``colorspace`` and must be set by
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the driver for capture streams and by the application for output
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streams, see :ref:`colorspaces`.
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