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+<refentry id="vidioc-decoder-cmd">
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+ <refmeta>
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+ <refentrytitle>ioctl VIDIOC_DECODER_CMD, VIDIOC_TRY_DECODER_CMD</refentrytitle>
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+ &manvol;
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+ </refmeta>
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+
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+ <refnamediv>
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+ <refname>VIDIOC_DECODER_CMD</refname>
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+ <refname>VIDIOC_TRY_DECODER_CMD</refname>
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+ <refpurpose>Execute an decoder command</refpurpose>
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+ </refnamediv>
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+
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+ <refsynopsisdiv>
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+ <funcsynopsis>
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+ <funcprototype>
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+ <funcdef>int <function>ioctl</function></funcdef>
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+ <paramdef>int <parameter>fd</parameter></paramdef>
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+ <paramdef>int <parameter>request</parameter></paramdef>
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+ <paramdef>struct v4l2_decoder_cmd *<parameter>argp</parameter></paramdef>
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+ </funcprototype>
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+ </funcsynopsis>
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+ </refsynopsisdiv>
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+
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+ <refsect1>
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+ <title>Arguments</title>
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+
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+ <variablelist>
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+ <varlistentry>
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+ <term><parameter>fd</parameter></term>
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+ <listitem>
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+ <para>&fd;</para>
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+ </listitem>
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+ </varlistentry>
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+ <varlistentry>
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+ <term><parameter>request</parameter></term>
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+ <listitem>
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+ <para>VIDIOC_DECODER_CMD, VIDIOC_TRY_DECODER_CMD</para>
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+ </listitem>
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+ </varlistentry>
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+ <varlistentry>
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+ <term><parameter>argp</parameter></term>
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+ <listitem>
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+ <para></para>
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+ </listitem>
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+ </varlistentry>
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+ </variablelist>
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+ </refsect1>
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+
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+ <refsect1>
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+ <title>Description</title>
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+
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+ <note>
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+ <title>Experimental</title>
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+
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+ <para>This is an <link linkend="experimental">experimental</link>
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+interface and may change in the future.</para>
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+ </note>
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+
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+ <para>These ioctls control an audio/video (usually MPEG-) decoder.
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+<constant>VIDIOC_DECODER_CMD</constant> sends a command to the
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+decoder, <constant>VIDIOC_TRY_DECODER_CMD</constant> can be used to
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+try a command without actually executing it. To send a command applications
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+must initialize all fields of a &v4l2-decoder-cmd; and call
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+<constant>VIDIOC_DECODER_CMD</constant> or <constant>VIDIOC_TRY_DECODER_CMD</constant>
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+with a pointer to this structure.</para>
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+
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+ <para>The <structfield>cmd</structfield> field must contain the
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+command code. Some commands use the <structfield>flags</structfield> field for
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+additional information.
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+</para>
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+
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+ <para>A <function>write</function>() or &VIDIOC-STREAMON; call sends an implicit
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+START command to the decoder if it has not been started yet.
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+</para>
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+
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+ <para>A <function>close</function>() or &VIDIOC-STREAMOFF; call of a streaming
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+file descriptor sends an implicit immediate STOP command to the decoder, and all
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+buffered data is discarded.</para>
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+
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+ <para>These ioctls are optional, not all drivers may support
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+them. They were introduced in Linux 3.3.</para>
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+
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+ <table pgwide="1" frame="none" id="v4l2-decoder-cmd">
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+ <title>struct <structname>v4l2_decoder_cmd</structname></title>
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+ <tgroup cols="5">
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+ &cs-str;
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+ <tbody valign="top">
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+ <row>
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+ <entry>__u32</entry>
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+ <entry><structfield>cmd</structfield></entry>
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+ <entry></entry>
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+ <entry></entry>
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+ <entry>The decoder command, see <xref linkend="decoder-cmds" />.</entry>
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+ </row>
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+ <row>
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+ <entry>__u32</entry>
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+ <entry><structfield>flags</structfield></entry>
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+ <entry></entry>
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+ <entry></entry>
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+ <entry>Flags to go with the command. If no flags are defined for
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+this command, drivers and applications must set this field to zero.</entry>
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+ </row>
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+ <row>
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+ <entry>union</entry>
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+ <entry>(anonymous)</entry>
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+ <entry></entry>
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+ <entry></entry>
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+ <entry></entry>
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+ </row>
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+ <row>
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+ <entry></entry>
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+ <entry>struct</entry>
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+ <entry><structfield>start</structfield></entry>
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+ <entry></entry>
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+ <entry>Structure containing additional data for the
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+<constant>V4L2_DEC_CMD_START</constant> command.</entry>
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+ </row>
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+ <row>
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+ <entry></entry>
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+ <entry></entry>
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+ <entry>__u32</entry>
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+ <entry><structfield>speed</structfield></entry>
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+ <entry>Playback speed and direction. The playback speed is defined as
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+<structfield>speed</structfield>/1000 of the normal speed. So 1000 is normal playback.
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+Negative numbers denote reverse playback, so -1000 does reverse playback at normal
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+speed. Speeds -1, 0 and 1 have special meanings: speed 0 is shorthand for 1000
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+(normal playback). A speed of 1 steps just one frame forward, a speed of -1 steps
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+just one frame back.
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+ </entry>
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+ </row>
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+ <row>
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+ <entry></entry>
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+ <entry></entry>
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+ <entry>__u32</entry>
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+ <entry><structfield>format</structfield></entry>
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+ <entry>Format restrictions. This field is set by the driver, not the
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+application. Possible values are <constant>V4L2_DEC_START_FMT_NONE</constant> if
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+there are no format restrictions or <constant>V4L2_DEC_START_FMT_GOP</constant>
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+if the decoder operates on full GOPs (<wordasword>Group Of Pictures</wordasword>).
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+This is usually the case for reverse playback: the decoder needs full GOPs, which
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+it can then play in reverse order. So to implement reverse playback the application
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+must feed the decoder the last GOP in the video file, then the GOP before that, etc. etc.
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+ </entry>
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+ </row>
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+ <row>
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+ <entry></entry>
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+ <entry>struct</entry>
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+ <entry><structfield>stop</structfield></entry>
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+ <entry></entry>
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+ <entry>Structure containing additional data for the
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+<constant>V4L2_DEC_CMD_STOP</constant> command.</entry>
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+ </row>
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+ <row>
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+ <entry></entry>
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+ <entry></entry>
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+ <entry>__u64</entry>
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+ <entry><structfield>pts</structfield></entry>
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+ <entry>Stop playback at this <structfield>pts</structfield> or immediately
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+if the playback is already past that timestamp. Leave to 0 if you want to stop after the
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+last frame was decoded.
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+ </entry>
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+ </row>
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+ <row>
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+ <entry></entry>
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+ <entry>struct</entry>
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+ <entry><structfield>raw</structfield></entry>
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+ <entry></entry>
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+ <entry></entry>
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+ </row>
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+ <row>
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+ <entry></entry>
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+ <entry></entry>
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+ <entry>__u32</entry>
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+ <entry><structfield>data</structfield>[16]</entry>
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+ <entry>Reserved for future extensions. Drivers and
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+applications must set the array to zero.</entry>
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+ </row>
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+ </tbody>
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+ </tgroup>
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+ </table>
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+
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+ <table pgwide="1" frame="none" id="decoder-cmds">
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+ <title>Decoder Commands</title>
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+ <tgroup cols="3">
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+ &cs-def;
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+ <tbody valign="top">
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+ <row>
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+ <entry><constant>V4L2_DEC_CMD_START</constant></entry>
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+ <entry>0</entry>
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+ <entry>Start the decoder. When the decoder is already
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+running or paused, this command will just change the playback speed.
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+That means that calling <constant>V4L2_DEC_CMD_START</constant> when
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+the decoder was paused will <emphasis>not</emphasis> resume the decoder.
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+You have to explicitly call <constant>V4L2_DEC_CMD_RESUME</constant> for that.
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+This command has one flag:
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+<constant>V4L2_DEC_CMD_START_MUTE_AUDIO</constant>. If set, then audio will
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+be muted when playing back at a non-standard speed.
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+ </entry>
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+ </row>
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+ <row>
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+ <entry><constant>V4L2_DEC_CMD_STOP</constant></entry>
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+ <entry>1</entry>
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+ <entry>Stop the decoder. When the decoder is already stopped,
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+this command does nothing. This command has two flags:
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+if <constant>V4L2_DEC_CMD_STOP_TO_BLACK</constant> is set, then the decoder will
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+set the picture to black after it stopped decoding. Otherwise the last image will
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+repeat. If <constant>V4L2_DEC_CMD_STOP_IMMEDIATELY</constant> is set, then the decoder
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+stops immediately (ignoring the <structfield>pts</structfield> value), otherwise it
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+will keep decoding until timestamp >= pts or until the last of the pending data from
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+its internal buffers was decoded.
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+</entry>
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+ </row>
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+ <row>
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+ <entry><constant>V4L2_DEC_CMD_PAUSE</constant></entry>
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+ <entry>2</entry>
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+ <entry>Pause the decoder. When the decoder has not been
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+started yet, the driver will return an &EPERM;. When the decoder is
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+already paused, this command does nothing. This command has one flag:
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+if <constant>V4L2_DEC_CMD_PAUSE_TO_BLACK</constant> is set, then set the
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+decoder output to black when paused.
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+</entry>
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+ </row>
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+ <row>
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+ <entry><constant>V4L2_DEC_CMD_RESUME</constant></entry>
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+ <entry>3</entry>
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+ <entry>Resume decoding after a PAUSE command. When the
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+decoder has not been started yet, the driver will return an &EPERM;.
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+When the decoder is already running, this command does nothing. No
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+flags are defined for this command.</entry>
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+ </row>
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+ </tbody>
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+ </tgroup>
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+ </table>
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+
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+ </refsect1>
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+
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+ <refsect1>
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+ &return-value;
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+
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+ <variablelist>
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+ <varlistentry>
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+ <term><errorcode>EINVAL</errorcode></term>
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+ <listitem>
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+ <para>The <structfield>cmd</structfield> field is invalid.</para>
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+ </listitem>
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+ </varlistentry>
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+ <varlistentry>
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+ <term><errorcode>EPERM</errorcode></term>
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+ <listitem>
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+ <para>The application sent a PAUSE or RESUME command when
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+the decoder was not running.</para>
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+ </listitem>
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+ </varlistentry>
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+ </variablelist>
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+ </refsect1>
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+</refentry>
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