<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>. 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 the &v4l2-pix-format; <structfield>pix</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 input is ambiguous, 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> <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>&v4l2-buf-type;</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-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 and custom (driver defined) formats with <structfield>type</structfield> <constant>V4L2_BUF_TYPE_PRIVATE</constant> and higher.</entry> </row> </tbody> </tgroup> </table> </refsect1> <refsect1> &return-value; <variablelist> <varlistentry> <term><errorcode>EBUSY</errorcode></term> <listitem> <para>The data format cannot be changed at this time, for example because I/O is already in progress.</para> </listitem> </varlistentry> <varlistentry> <term><errorcode>EINVAL</errorcode></term> <listitem> <para>The &v4l2-format; <structfield>type</structfield> field is invalid, the requested buffer type not supported, or <constant>VIDIOC_TRY_FMT</constant> was called and is not supported with this buffer type.</para> </listitem> </varlistentry> </variablelist> </refsect1> </refentry> <!-- Local Variables: mode: sgml sgml-parent-document: "v4l2.sgml" indent-tabs-mode: nil End: -->