planar-apis.rst (2664B)
1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later 2 3.. _planar-apis: 4 5***************************** 6Single- and multi-planar APIs 7***************************** 8 9Some devices require data for each input or output video frame to be 10placed in discontiguous memory buffers. In such cases, one video frame 11has to be addressed using more than one memory address, i.e. one pointer 12per "plane". A plane is a sub-buffer of the current frame. For examples 13of such formats see :ref:`pixfmt`. 14 15Initially, V4L2 API did not support multi-planar buffers and a set of 16extensions has been introduced to handle them. Those extensions 17constitute what is being referred to as the "multi-planar API". 18 19Some of the V4L2 API calls and structures are interpreted differently, 20depending on whether single- or multi-planar API is being used. An 21application can choose whether to use one or the other by passing a 22corresponding buffer type to its ioctl calls. Multi-planar versions of 23buffer types are suffixed with an ``_MPLANE`` string. For a list of 24available multi-planar buffer types see enum 25:c:type:`v4l2_buf_type`. 26 27 28Multi-planar formats 29==================== 30 31Multi-planar API introduces new multi-planar formats. Those formats use 32a separate set of FourCC codes. It is important to distinguish between 33the multi-planar API and a multi-planar format. Multi-planar API calls 34can handle all single-planar formats as well (as long as they are passed 35in multi-planar API structures), while the single-planar API cannot 36handle multi-planar formats. 37 38 39Calls that distinguish between single and multi-planar APIs 40=========================================================== 41 42:ref:`VIDIOC_QUERYCAP <VIDIOC_QUERYCAP>` 43 Two additional multi-planar capabilities are added. They can be set 44 together with non-multi-planar ones for devices that handle both 45 single- and multi-planar formats. 46 47:ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>`, :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>`, :ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>` 48 New structures for describing multi-planar formats are added: struct 49 :c:type:`v4l2_pix_format_mplane` and 50 struct :c:type:`v4l2_plane_pix_format`. 51 Drivers may define new multi-planar formats, which have distinct 52 FourCC codes from the existing single-planar ones. 53 54:ref:`VIDIOC_QBUF <VIDIOC_QBUF>`, :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>`, :ref:`VIDIOC_QUERYBUF <VIDIOC_QUERYBUF>` 55 A new struct :c:type:`v4l2_plane` structure for 56 describing planes is added. Arrays of this structure are passed in 57 the new ``m.planes`` field of struct 58 :c:type:`v4l2_buffer`. 59 60:ref:`VIDIOC_REQBUFS <VIDIOC_REQBUFS>` 61 Will allocate multi-planar buffers as requested.