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+<refentry id="vidioc-g-fmt">
+ <refmeta>
+ <refentrytitle>ioctl VIDIOC_G_FMT, VIDIOC_S_FMT,
+VIDIOC_TRY_FMT</refentrytitle>
+ &manvol;
+ </refmeta>
+
+ <refnamediv>
+ <refname>VIDIOC_G_FMT</refname>
+ <refname>VIDIOC_S_FMT</refname>
+ <refname>VIDIOC_TRY_FMT</refname>
+ <refpurpose>Get or set the data format, try a format</refpurpose>
+ </refnamediv>
+
+ <refsynopsisdiv>
+ <funcsynopsis>
+ <funcprototype>
+ <funcdef>int <function>ioctl</function></funcdef>
+ <paramdef>int <parameter>fd</parameter></paramdef>
+ <paramdef>int <parameter>request</parameter></paramdef>
+ <paramdef>struct v4l2_format
+*<parameter>argp</parameter></paramdef>
+ </funcprototype>
+ </funcsynopsis>
+ </refsynopsisdiv>
+
+ <refsect1>
+ <title>Arguments</title>
+
+ <variablelist>
+ <varlistentry>
+ <term><parameter>fd</parameter></term>
+ <listitem>
+ <para>&fd;</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><parameter>request</parameter></term>
+ <listitem>
+ <para>VIDIOC_G_FMT, VIDIOC_S_FMT, VIDIOC_TRY_FMT</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><parameter>argp</parameter></term>
+ <listitem>
+ <para></para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ </refsect1>
+
+ <refsect1>
+ <title>Description</title>
+
+ <para>These ioctls are used to negotiate the format of data
+(typically image format) exchanged between driver and
+application.</para>
+
+ <para>To query the current parameters applications set the
+<structfield>type</structfield> field of a struct
+<structname>v4l2_format</structname> to the respective buffer (stream)
+type. For example video capture devices use
+<constant>V4L2_BUF_TYPE_VIDEO_CAPTURE</constant> or
+<constant>V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE</constant>. When the application
+calls the <constant>VIDIOC_G_FMT</constant> ioctl with a pointer to
+this structure the driver fills the respective member of the
+<structfield>fmt</structfield> union. In case of video capture devices
+that is either the &v4l2-pix-format; <structfield>pix</structfield> or
+the &v4l2-pix-format-mplane; <structfield>pix_mp</structfield> member.
+When the requested buffer type is not supported drivers return an
+&EINVAL;.</para>
+
+ <para>To change the current format parameters applications
+initialize the <structfield>type</structfield> field and all
+fields of the respective <structfield>fmt</structfield>
+union member. For details see the documentation of the various devices
+types in <xref linkend="devices" />. Good practice is to query the
+current parameters first, and to
+modify only those parameters not suitable for the application. When
+the application calls the <constant>VIDIOC_S_FMT</constant> ioctl
+with a pointer to a <structname>v4l2_format</structname> structure
+the driver checks
+and adjusts the parameters against hardware abilities. Drivers
+should not return an error code unless the <structfield>type</structfield> field is invalid, this is
+a mechanism to fathom device capabilities and to approach parameters
+acceptable for both the application and driver. On success the driver
+may program the hardware, allocate resources and generally prepare for
+data exchange.
+Finally the <constant>VIDIOC_S_FMT</constant> ioctl returns the
+current format parameters as <constant>VIDIOC_G_FMT</constant> does.
+Very simple, inflexible devices may even ignore all input and always
+return the default parameters. However all V4L2 devices exchanging
+data with the application must implement the
+<constant>VIDIOC_G_FMT</constant> and
+<constant>VIDIOC_S_FMT</constant> ioctl. When the requested buffer
+type is not supported drivers return an &EINVAL; on a
+<constant>VIDIOC_S_FMT</constant> attempt. When I/O is already in
+progress or the resource is not available for other reasons drivers
+return the &EBUSY;.</para>
+
+ <para>The <constant>VIDIOC_TRY_FMT</constant> ioctl is equivalent
+to <constant>VIDIOC_S_FMT</constant> with one exception: it does not
+change driver state. It can also be called at any time, never
+returning <errorcode>EBUSY</errorcode>. This function is provided to
+negotiate parameters, to learn about hardware limitations, without
+disabling I/O or possibly time consuming hardware preparations.
+Although strongly recommended drivers are not required to implement
+this ioctl.</para>
+
+ <para>The format as returned by <constant>VIDIOC_TRY_FMT</constant>
+must be identical to what <constant>VIDIOC_S_FMT</constant> returns for
+the same input or output.</para>
+
+ <table pgwide="1" frame="none" id="v4l2-format">
+ <title>struct <structname>v4l2_format</structname></title>
+ <tgroup cols="4">
+ <colspec colname="c1" />
+ <colspec colname="c2" />
+ <colspec colname="c3" />
+ <colspec colname="c4" />
+ <tbody valign="top">
+ <row>
+ <entry>__u32</entry>
+ <entry><structfield>type</structfield></entry>
+ <entry></entry>
+ <entry>Type of the data stream, see <xref
+ linkend="v4l2-buf-type" />.</entry>
+ </row>
+ <row>
+ <entry>union</entry>
+ <entry><structfield>fmt</structfield></entry>
+ </row>
+ <row>
+ <entry></entry>
+ <entry>&v4l2-pix-format;</entry>
+ <entry><structfield>pix</structfield></entry>
+ <entry>Definition of an image format, see <xref
+ linkend="pixfmt" />, used by video capture and output
+devices.</entry>
+ </row>
+ <row>
+ <entry></entry>
+ <entry>&v4l2-pix-format-mplane;</entry>
+ <entry><structfield>pix_mp</structfield></entry>
+ <entry>Definition of an image format, see <xref
+ linkend="pixfmt" />, used by video capture and output
+devices that support the <link linkend="planar-apis">multi-planar
+version of the API</link>.</entry>
+ </row>
+ <row>
+ <entry></entry>
+ <entry>&v4l2-window;</entry>
+ <entry><structfield>win</structfield></entry>
+ <entry>Definition of an overlaid image, see <xref
+ linkend="overlay" />, used by video overlay devices.</entry>
+ </row>
+ <row>
+ <entry></entry>
+ <entry>&v4l2-vbi-format;</entry>
+ <entry><structfield>vbi</structfield></entry>
+ <entry>Raw VBI capture or output parameters. This is
+discussed in more detail in <xref linkend="raw-vbi" />. Used by raw VBI
+capture and output devices.</entry>
+ </row>
+ <row>
+ <entry></entry>
+ <entry>&v4l2-sliced-vbi-format;</entry>
+ <entry><structfield>sliced</structfield></entry>
+ <entry>Sliced VBI capture or output parameters. See
+<xref linkend="sliced" /> for details. Used by sliced VBI
+capture and output devices.</entry>
+ </row>
+ <row>
+ <entry></entry>
+ <entry>__u8</entry>
+ <entry><structfield>raw_data</structfield>[200]</entry>
+ <entry>Place holder for future extensions.</entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </table>
+ </refsect1>
+
+ <refsect1>
+ &return-value;
+
+ <variablelist>
+ <varlistentry>
+ <term><errorcode>EINVAL</errorcode></term>
+ <listitem>
+ <para>The &v4l2-format; <structfield>type</structfield>
+field is invalid or the requested buffer type not supported.</para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ </refsect1>
+</refentry>