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-<refentry id="vidioc-g-parm">
- <refmeta>
- <refentrytitle>ioctl VIDIOC_G_PARM, VIDIOC_S_PARM</refentrytitle>
- &manvol;
- </refmeta>
-
- <refnamediv>
- <refname>VIDIOC_G_PARM</refname>
- <refname>VIDIOC_S_PARM</refname>
- <refpurpose>Get or set streaming parameters</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_streamparm *<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_PARM, VIDIOC_S_PARM</para>
- </listitem>
- </varlistentry>
- <varlistentry>
- <term><parameter>argp</parameter></term>
- <listitem>
- <para></para>
- </listitem>
- </varlistentry>
- </variablelist>
- </refsect1>
-
- <refsect1>
- <title>Description</title>
-
- <para>The current video standard determines a nominal number of
-frames per second. If less than this number of frames is to be
-captured or output, applications can request frame skipping or
-duplicating on the driver side. This is especially useful when using
-the <function>read()</function> or <function>write()</function>, which
-are not augmented by timestamps or sequence counters, and to avoid
-unnecessary data copying.</para>
-
- <para>Further these ioctls can be used to determine the number of
-buffers used internally by a driver in read/write mode. For
-implications see the section discussing the &func-read;
-function.</para>
-
- <para>To get and set the streaming parameters applications call
-the <constant>VIDIOC_G_PARM</constant> and
-<constant>VIDIOC_S_PARM</constant> ioctl, respectively. They take a
-pointer to a struct <structname>v4l2_streamparm</structname> which
-contains a union holding separate parameters for input and output
-devices.</para>
-
- <table pgwide="1" frame="none" id="v4l2-streamparm">
- <title>struct <structname>v4l2_streamparm</structname></title>
- <tgroup cols="4">
- &cs-ustr;
- <tbody valign="top">
- <row>
- <entry>__u32</entry>
- <entry><structfield>type</structfield></entry>
- <entry></entry>
- <entry>The buffer (stream) type, same as &v4l2-format;
-<structfield>type</structfield>, set by the application. See <xref
- linkend="v4l2-buf-type" /></entry>
- </row>
- <row>
- <entry>union</entry>
- <entry><structfield>parm</structfield></entry>
- <entry></entry>
- <entry></entry>
- </row>
- <row>
- <entry></entry>
- <entry>&v4l2-captureparm;</entry>
- <entry><structfield>capture</structfield></entry>
- <entry>Parameters for capture devices, used when
-<structfield>type</structfield> is
-<constant>V4L2_BUF_TYPE_VIDEO_CAPTURE</constant>.</entry>
- </row>
- <row>
- <entry></entry>
- <entry>&v4l2-outputparm;</entry>
- <entry><structfield>output</structfield></entry>
- <entry>Parameters for output devices, used when
-<structfield>type</structfield> is
-<constant>V4L2_BUF_TYPE_VIDEO_OUTPUT</constant>.</entry>
- </row>
- <row>
- <entry></entry>
- <entry>__u8</entry>
- <entry><structfield>raw_data</structfield>[200]</entry>
- <entry>A place holder for future extensions and custom
-(driver defined) buffer types <constant>V4L2_BUF_TYPE_PRIVATE</constant> and
-higher.</entry>
- </row>
- </tbody>
- </tgroup>
- </table>
-
- <table pgwide="1" frame="none" id="v4l2-captureparm">
- <title>struct <structname>v4l2_captureparm</structname></title>
- <tgroup cols="3">
- &cs-str;
- <tbody valign="top">
- <row>
- <entry>__u32</entry>
- <entry><structfield>capability</structfield></entry>
- <entry>See <xref linkend="parm-caps" />.</entry>
- </row>
- <row>
- <entry>__u32</entry>
- <entry><structfield>capturemode</structfield></entry>
- <entry>Set by drivers and applications, see <xref linkend="parm-flags" />.</entry>
- </row>
- <row>
- <entry>&v4l2-fract;</entry>
- <entry><structfield>timeperframe</structfield></entry>
- <entry><para>This is is the desired period between
-successive frames captured by the driver, in seconds. The
-field is intended to skip frames on the driver side, saving I/O
-bandwidth.</para><para>Applications store here the desired frame
-period, drivers return the actual frame period, which must be greater
-or equal to the nominal frame period determined by the current video
-standard (&v4l2-standard; <structfield>frameperiod</structfield>
-field). Changing the video standard (also implicitly by switching the
-video input) may reset this parameter to the nominal frame period. To
-reset manually applications can just set this field to
-zero.</para><para>Drivers support this function only when they set the
-<constant>V4L2_CAP_TIMEPERFRAME</constant> flag in the
-<structfield>capability</structfield> field.</para></entry>
- </row>
- <row>
- <entry>__u32</entry>
- <entry><structfield>extendedmode</structfield></entry>
- <entry>Custom (driver specific) streaming parameters. When
-unused, applications and drivers must set this field to zero.
-Applications using this field should check the driver name and
-version, see <xref linkend="querycap" />.</entry>
- </row>
- <row>
- <entry>__u32</entry>
- <entry><structfield>readbuffers</structfield></entry>
- <entry>Applications set this field to the desired number
-of buffers used internally by the driver in &func-read; mode. Drivers
-return the actual number of buffers. When an application requests zero
-buffers, drivers should just return the current setting rather than
-the minimum or an error code. For details see <xref
- linkend="rw" />.</entry>
- </row>
- <row>
- <entry>__u32</entry>
- <entry><structfield>reserved</structfield>[4]</entry>
- <entry>Reserved for future extensions. Drivers and
-applications must set the array to zero.</entry>
- </row>
- </tbody>
- </tgroup>
- </table>
-
- <table pgwide="1" frame="none" id="v4l2-outputparm">
- <title>struct <structname>v4l2_outputparm</structname></title>
- <tgroup cols="3">
- &cs-str;
- <tbody valign="top">
- <row>
- <entry>__u32</entry>
- <entry><structfield>capability</structfield></entry>
- <entry>See <xref linkend="parm-caps" />.</entry>
- </row>
- <row>
- <entry>__u32</entry>
- <entry><structfield>outputmode</structfield></entry>
- <entry>Set by drivers and applications, see <xref
- linkend="parm-flags" />.</entry>
- </row>
- <row>
- <entry>&v4l2-fract;</entry>
- <entry><structfield>timeperframe</structfield></entry>
- <entry>This is is the desired period between
-successive frames output by the driver, in seconds.</entry>
- </row>
- <row>
- <entry spanname="hspan"><para>The field is intended to
-repeat frames on the driver side in &func-write; mode (in streaming
-mode timestamps can be used to throttle the output), saving I/O
-bandwidth.</para><para>Applications store here the desired frame
-period, drivers return the actual frame period, which must be greater
-or equal to the nominal frame period determined by the current video
-standard (&v4l2-standard; <structfield>frameperiod</structfield>
-field). Changing the video standard (also implicitly by switching the
-video output) may reset this parameter to the nominal frame period. To
-reset manually applications can just set this field to
-zero.</para><para>Drivers support this function only when they set the
-<constant>V4L2_CAP_TIMEPERFRAME</constant> flag in the
-<structfield>capability</structfield> field.</para></entry>
- </row>
- <row>
- <entry>__u32</entry>
- <entry><structfield>extendedmode</structfield></entry>
- <entry>Custom (driver specific) streaming parameters. When
-unused, applications and drivers must set this field to zero.
-Applications using this field should check the driver name and
-version, see <xref linkend="querycap" />.</entry>
- </row>
- <row>
- <entry>__u32</entry>
- <entry><structfield>writebuffers</structfield></entry>
- <entry>Applications set this field to the desired number
-of buffers used internally by the driver in
-<function>write()</function> mode. Drivers return the actual number of
-buffers. When an application requests zero buffers, drivers should
-just return the current setting rather than the minimum or an error
-code. For details see <xref linkend="rw" />.</entry>
- </row>
- <row>
- <entry>__u32</entry>
- <entry><structfield>reserved</structfield>[4]</entry>
- <entry>Reserved for future extensions. Drivers and
-applications must set the array to zero.</entry>
- </row>
- </tbody>
- </tgroup>
- </table>
-
- <table pgwide="1" frame="none" id="parm-caps">
- <title>Streaming Parameters Capabilites</title>
- <tgroup cols="3">
- &cs-def;
- <tbody valign="top">
- <row>
- <entry><constant>V4L2_CAP_TIMEPERFRAME</constant></entry>
- <entry>0x1000</entry>
- <entry>The frame skipping/repeating controlled by the
-<structfield>timeperframe</structfield> field is supported.</entry>
- </row>
- </tbody>
- </tgroup>
- </table>
-
- <table pgwide="1" frame="none" id="parm-flags">
- <title>Capture Parameters Flags</title>
- <tgroup cols="3">
- &cs-def;
- <tbody valign="top">
- <row>
- <entry><constant>V4L2_MODE_HIGHQUALITY</constant></entry>
- <entry>0x0001</entry>
- <entry><para>High quality imaging mode. High quality mode
-is intended for still imaging applications. The idea is to get the
-best possible image quality that the hardware can deliver. It is not
-defined how the driver writer may achieve that; it will depend on the
-hardware and the ingenuity of the driver writer. High quality mode is
-a different mode from the the regular motion video capture modes. In
-high quality mode:<itemizedlist>
- <listitem>
- <para>The driver may be able to capture higher
-resolutions than for motion capture.</para>
- </listitem>
- <listitem>
- <para>The driver may support fewer pixel formats
-than motion capture (eg; true color).</para>
- </listitem>
- <listitem>
- <para>The driver may capture and arithmetically
-combine multiple successive fields or frames to remove color edge
-artifacts and reduce the noise in the video data.
-</para>
- </listitem>
- <listitem>
- <para>The driver may capture images in slices like
-a scanner in order to handle larger format images than would otherwise
-be possible. </para>
- </listitem>
- <listitem>
- <para>An image capture operation may be
-significantly slower than motion capture. </para>
- </listitem>
- <listitem>
- <para>Moving objects in the image might have
-excessive motion blur. </para>
- </listitem>
- <listitem>
- <para>Capture might only work through the
-<function>read()</function> call.</para>
- </listitem>
- </itemizedlist></para></entry>
- </row>
- </tbody>
- </tgroup>
- </table>
-
- </refsect1>
-
- <refsect1>
- &return-value;
- </refsect1>
-</refentry>