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-<section id="planar-apis">
- <title>Single- and multi-planar APIs</title>
- <para>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 <xref linkend="pixfmt" />.</para>
- <para>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".</para>
- <para>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 &v4l2-buf-type;.
- </para>
- <section>
- <title>Multi-planar formats</title>
- <para>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.</para>
- </section>
- <section>
- <title>Calls that distinguish between single and multi-planar APIs</title>
- <variablelist>
- <varlistentry>
- <term>&VIDIOC-QUERYCAP;</term>
- <listitem><para>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.</para></listitem>
- </varlistentry>
- <varlistentry>
- <listitem><para>New structures for describing multi-planar formats are added:
- &v4l2-pix-format-mplane; and &v4l2-plane-pix-format;. Drivers may
- define new multi-planar formats, which have distinct FourCC codes from
- the existing single-planar ones.</para>
- </listitem>
- </varlistentry>
- <varlistentry>
- <listitem><para>A new &v4l2-plane; structure for describing planes is added.
- Arrays of this structure are passed in the new
- <structfield>m.planes</structfield> field of &v4l2-buffer;.</para>
- </listitem>
- </varlistentry>
- <varlistentry>
- <term>&VIDIOC-REQBUFS;</term>
- <listitem><para>Will allocate multi-planar buffers as requested.</para></listitem>
- </varlistentry>
- </variablelist>
- </section>