62 lines
2.6 KiB
ReStructuredText
62 lines
2.6 KiB
ReStructuredText
|
.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
|
||
|
|
|
||
|
|
.. _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.
|