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- .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
- .. c:namespace:: V4L
- .. _planar-apis:
- *****************************
- Single- and multi-planar APIs
- *****************************
- Some devices require data for each input or output video frame to be
- placed in discontiguous memory buffers. In such cases, one video frame
- has to be addressed using more than one memory address, i.e. one pointer
- per "plane". A plane is a sub-buffer of the current frame. For examples
- of such formats see :ref:`pixfmt`.
- Initially, V4L2 API did not support multi-planar buffers and a set of
- extensions has been introduced to handle them. Those extensions
- constitute what is being referred to as the "multi-planar API".
- Some of the V4L2 API calls and structures are interpreted differently,
- depending on whether single- or multi-planar API is being used. An
- application can choose whether to use one or the other by passing a
- corresponding buffer type to its ioctl calls. Multi-planar versions of
- buffer types are suffixed with an ``_MPLANE`` string. For a list of
- available multi-planar buffer types see enum
- :c:type:`v4l2_buf_type`.
- Multi-planar formats
- ====================
- Multi-planar API introduces new multi-planar formats. Those formats use
- a separate set of FourCC codes. It is important to distinguish between
- the multi-planar API and a multi-planar format. Multi-planar API calls
- can handle all single-planar formats as well (as long as they are passed
- in multi-planar API structures), while the single-planar API cannot
- handle multi-planar formats.
- Calls that distinguish between single and multi-planar APIs
- ===========================================================
- :ref:`VIDIOC_QUERYCAP <VIDIOC_QUERYCAP>`
- Two additional multi-planar capabilities are added. They can be set
- together with non-multi-planar ones for devices that handle both
- single- and multi-planar formats.
- :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>`, :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>`, :ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>`
- New structures for describing multi-planar formats are added: struct
- :c:type:`v4l2_pix_format_mplane` and
- struct :c:type:`v4l2_plane_pix_format`.
- Drivers may define new multi-planar formats, which have distinct
- FourCC codes from the existing single-planar ones.
- :ref:`VIDIOC_QBUF <VIDIOC_QBUF>`, :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>`, :ref:`VIDIOC_QUERYBUF <VIDIOC_QUERYBUF>`
- A new struct :c:type:`v4l2_plane` structure for
- describing planes is added. Arrays of this structure are passed in
- the new ``m.planes`` field of struct
- :c:type:`v4l2_buffer`.
- :ref:`VIDIOC_REQBUFS <VIDIOC_REQBUFS>`
- Will allocate multi-planar buffers as requested.
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