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Diffstat (limited to 'Documentation/DocBook/media/v4l/vidioc-g-parm.xml')
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diff --git a/Documentation/DocBook/media/v4l/vidioc-g-parm.xml b/Documentation/DocBook/media/v4l/vidioc-g-parm.xml new file mode 100644 index 00000000..19b1d85d --- /dev/null +++ b/Documentation/DocBook/media/v4l/vidioc-g-parm.xml @@ -0,0 +1,315 @@ +<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>&v4l2-buf-type;</entry> + <entry><structfield>type</structfield></entry> + <entry></entry> + <entry>The buffer (stream) type, same as &v4l2-format; +<structfield>type</structfield>, set by the application.</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> |