linux-vybrid_public/Documentation/DocBook/media/v4l/vidioc-encoder-cmd.xml

<refentry id="vidioc-encoder-cmd">
  <refmeta>
    <refentrytitle>ioctl VIDIOC_ENCODER_CMD, VIDIOC_TRY_ENCODER_CMD</refentrytitle>
    &manvol;
  </refmeta>

  <refnamediv>
    <refname>VIDIOC_ENCODER_CMD</refname>
    <refname>VIDIOC_TRY_ENCODER_CMD</refname>
    <refpurpose>Execute an encoder command</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_encoder_cmd *<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_ENCODER_CMD, VIDIOC_TRY_ENCODER_CMD</para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term><parameter>argp</parameter></term>
	<listitem>
	  <para></para>
	</listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1>
    <title>Description</title>

    <para>These ioctls control an audio/video (usually MPEG-) encoder.
<constant>VIDIOC_ENCODER_CMD</constant> sends a command to the
encoder, <constant>VIDIOC_TRY_ENCODER_CMD</constant> can be used to
try a command without actually executing it.</para>

    <para>To send a command applications must initialize all fields of a
    &v4l2-encoder-cmd; and call
    <constant>VIDIOC_ENCODER_CMD</constant> or
    <constant>VIDIOC_TRY_ENCODER_CMD</constant> with a pointer to this
    structure.</para>

    <para>The <structfield>cmd</structfield> field must contain the
command code. The <structfield>flags</structfield> field is currently
only used by the STOP command and contains one bit: If the
<constant>V4L2_ENC_CMD_STOP_AT_GOP_END</constant> flag is set,
encoding will continue until the end of the current <wordasword>Group
Of Pictures</wordasword>, otherwise it will stop immediately.</para>

    <para>A <function>read</function>() or &VIDIOC-STREAMON; call sends an implicit
START command to the encoder if it has not been started yet. After a STOP command,
<function>read</function>() calls will read the remaining data
buffered by the driver. When the buffer is empty,
<function>read</function>() will return zero and the next
<function>read</function>() call will restart the encoder.</para>

    <para>A <function>close</function>() or &VIDIOC-STREAMOFF; call of a streaming
file descriptor sends an implicit immediate STOP to the encoder, and all buffered
data is discarded.</para>

    <para>These ioctls are optional, not all drivers may support
them. They were introduced in Linux 2.6.21.</para>

    <table pgwide="1" frame="none" id="v4l2-encoder-cmd">
      <title>struct <structname>v4l2_encoder_cmd</structname></title>
      <tgroup cols="3">
	&cs-str;
	<tbody valign="top">
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>cmd</structfield></entry>
	    <entry>The encoder command, see <xref linkend="encoder-cmds" />.</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>flags</structfield></entry>
	    <entry>Flags to go with the command, see <xref
		linkend="encoder-flags" />. If no flags are defined for
this command, drivers and applications must set this field to
zero.</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>data</structfield>[8]</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="encoder-cmds">
      <title>Encoder Commands</title>
      <tgroup cols="3">
	&cs-def;
	<tbody valign="top">
	  <row>
	    <entry><constant>V4L2_ENC_CMD_START</constant></entry>
	    <entry>0</entry>
	    <entry>Start the encoder. When the encoder is already
running or paused, this command does nothing. No flags are defined for
this command.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_ENC_CMD_STOP</constant></entry>
	    <entry>1</entry>
	    <entry>Stop the encoder. When the
<constant>V4L2_ENC_CMD_STOP_AT_GOP_END</constant> flag is set,
encoding will continue until the end of the current <wordasword>Group
Of Pictures</wordasword>, otherwise encoding will stop immediately.
When the encoder is already stopped, this command does
nothing.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_ENC_CMD_PAUSE</constant></entry>
	    <entry>2</entry>
	    <entry>Pause the encoder. When the encoder has not been
started yet, the driver will return an &EPERM;. When the encoder is
already paused, this command does nothing. No flags are defined for
this command.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_ENC_CMD_RESUME</constant></entry>
	    <entry>3</entry>
	    <entry>Resume encoding after a PAUSE command. When the
encoder has not been started yet, the driver will return an &EPERM;.
When the encoder is already running, this command does nothing. No
flags are defined for this command.</entry>
	  </row>
	</tbody>
      </tgroup>
    </table>

    <table pgwide="1" frame="none" id="encoder-flags">
      <title>Encoder Command Flags</title>
      <tgroup cols="3">
	&cs-def;
	<tbody valign="top">
	  <row>
	    <entry><constant>V4L2_ENC_CMD_STOP_AT_GOP_END</constant></entry>
	    <entry>0x0001</entry>
	    <entry>Stop encoding at the end of the current <wordasword>Group Of
Pictures</wordasword>, rather than immediately.</entry>
	  </row>
       </tbody>
      </tgroup>
    </table>
  </refsect1>

  <refsect1>
    &return-value;

    <variablelist>
      <varlistentry>
	<term><errorcode>EINVAL</errorcode></term>
	<listitem>
	  <para>The <structfield>cmd</structfield> field is invalid.</para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term><errorcode>EPERM</errorcode></term>
	<listitem>
	  <para>The application sent a PAUSE or RESUME command when
the encoder was not running.</para>
	</listitem>
      </varlistentry>
    </variablelist>
  </refsect1>
</refentry>