<refentry id="vidioc-querystd">
  <refmeta>
    <refentrytitle>ioctl VIDIOC_QUERYSTD</refentrytitle>
    &manvol;
  </refmeta>

  <refnamediv>
    <refname>VIDIOC_QUERYSTD</refname>
    <refpurpose>Sense the video standard received by the current
input</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <funcsynopsis>
      <funcprototype>
	<funcdef>int <function>ioctl</function></funcdef>
	<paramdef>int <parameter>fd</parameter></paramdef>
	<paramdef>int <parameter>request</parameter></paramdef>
	<paramdef>v4l2_std_id *<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_QUERYSTD</para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term><parameter>argp</parameter></term>
	<listitem>
	  <para></para>
	</listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1>
    <title>Description</title>

    <para>The hardware may be able to detect the current video
standard automatically. To do so, applications call <constant>
VIDIOC_QUERYSTD</constant> with a pointer to a &v4l2-std-id; type. The
driver stores here a set of candidates, this can be a single flag or a
set of supported standards if for example the hardware can only
distinguish between 50 and 60 Hz systems. If no signal was detected,
then the driver will return V4L2_STD_UNKNOWN. When detection is not
possible or fails, the set must contain all standards supported by the
current video input or output.</para>

<para>Please note that drivers shall <emphasis>not</emphasis> switch the video standard
automatically if a new video standard is detected. Instead, drivers should send the
<constant>V4L2_EVENT_SOURCE_CHANGE</constant> event (if they support this) and expect
that userspace will take action by calling <constant>VIDIOC_QUERYSTD</constant>.
The reason is that a new video standard can mean different buffer sizes as well, and you
cannot change buffer sizes on the fly. In general, applications that receive the
Source Change event will have to call <constant>VIDIOC_QUERYSTD</constant>,
and if the detected video standard is valid they will have to stop streaming, set the new
standard, allocate new buffers and start streaming again.</para>

  </refsect1>

  <refsect1>
    &return-value;
    <variablelist>
      <varlistentry>
	<term><errorcode>ENODATA</errorcode></term>
	<listitem>
	  <para>Standard video timings are not supported for this input or output.</para>
	</listitem>
      </varlistentry>
    </variablelist>
  </refsect1>
</refentry>
