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

   1 <refentry id="vidioc-encoder-cmd">
   2   <refmeta>
   3     <refentrytitle>ioctl VIDIOC_ENCODER_CMD, VIDIOC_TRY_ENCODER_CMD</refentrytitle>
   4     &manvol;
   5   </refmeta>
   6
   7   <refnamediv>
   8     <refname>VIDIOC_ENCODER_CMD</refname>
   9     <refname>VIDIOC_TRY_ENCODER_CMD</refname>
  10     <refpurpose>Execute an encoder command</refpurpose>
  11   </refnamediv>
  12
  13   <refsynopsisdiv>
  14     <funcsynopsis>
  15       <funcprototype>
  16         <funcdef>int <function>ioctl</function></funcdef>
  17         <paramdef>int <parameter>fd</parameter></paramdef>
  18         <paramdef>int <parameter>request</parameter></paramdef>
  19         <paramdef>struct v4l2_encoder_cmd *<parameter>argp</parameter></paramdef>
  20       </funcprototype>
  21     </funcsynopsis>
  22   </refsynopsisdiv>
  23
  24   <refsect1>
  25     <title>Arguments</title>
  26
  27     <variablelist>
  28       <varlistentry>
  29         <term><parameter>fd</parameter></term>
  30         <listitem>
  31           <para>&fd;</para>
  32         </listitem>
  33       </varlistentry>
  34       <varlistentry>
  35         <term><parameter>request</parameter></term>
  36         <listitem>
  37           <para>VIDIOC_ENCODER_CMD, VIDIOC_TRY_ENCODER_CMD</para>
  38         </listitem>
  39       </varlistentry>
  40       <varlistentry>
  41         <term><parameter>argp</parameter></term>
  42         <listitem>
  43           <para></para>
  44         </listitem>
  45       </varlistentry>
  46     </variablelist>
  47   </refsect1>
  48
  49   <refsect1>
  50     <title>Description</title>
  51
  52     <para>These ioctls control an audio/video (usually MPEG-) encoder.
  53 <constant>VIDIOC_ENCODER_CMD</constant> sends a command to the
  54 encoder, <constant>VIDIOC_TRY_ENCODER_CMD</constant> can be used to
  55 try a command without actually executing it.</para>
  56
  57     <para>To send a command applications must initialize all fields of a
  58     &v4l2-encoder-cmd; and call
  59     <constant>VIDIOC_ENCODER_CMD</constant> or
  60     <constant>VIDIOC_TRY_ENCODER_CMD</constant> with a pointer to this
  61     structure.</para>
  62
  63     <para>The <structfield>cmd</structfield> field must contain the
  64 command code. The <structfield>flags</structfield> field is currently
  65 only used by the STOP command and contains one bit: If the
  66 <constant>V4L2_ENC_CMD_STOP_AT_GOP_END</constant> flag is set,
  67 encoding will continue until the end of the current <wordasword>Group
  68 Of Pictures</wordasword>, otherwise it will stop immediately.</para>
  69
  70     <para>A <function>read</function>() or &VIDIOC-STREAMON; call sends an implicit
  71 START command to the encoder if it has not been started yet. After a STOP command,
  72 <function>read</function>() calls will read the remaining data
  73 buffered by the driver. When the buffer is empty,
  74 <function>read</function>() will return zero and the next
  75 <function>read</function>() call will restart the encoder.</para>
  76
  77     <para>A <function>close</function>() or &VIDIOC-STREAMOFF; call of a streaming
  78 file descriptor sends an implicit immediate STOP to the encoder, and all buffered
  79 data is discarded.</para>
  80
  81     <para>These ioctls are optional, not all drivers may support
  82 them. They were introduced in Linux 2.6.21.</para>
  83
  84     <table pgwide="1" frame="none" id="v4l2-encoder-cmd">
  85       <title>struct <structname>v4l2_encoder_cmd</structname></title>
  86       <tgroup cols="3">
  87         &cs-str;
  88         <tbody valign="top">
  89           <row>
  90             <entry>__u32</entry>
  91             <entry><structfield>cmd</structfield></entry>
  92             <entry>The encoder command, see <xref linkend="encoder-cmds" />.</entry>
  93           </row>
  94           <row>
  95             <entry>__u32</entry>
  96             <entry><structfield>flags</structfield></entry>
  97             <entry>Flags to go with the command, see <xref
  98                 linkend="encoder-flags" />. If no flags are defined for
  99 this command, drivers and applications must set this field to
 100 zero.</entry>
 101           </row>
 102           <row>
 103             <entry>__u32</entry>
 104             <entry><structfield>data</structfield>[8]</entry>
 105             <entry>Reserved for future extensions. Drivers and
 106 applications must set the array to zero.</entry>
 107           </row>
 108         </tbody>
 109       </tgroup>
 110     </table>
 111
 112     <table pgwide="1" frame="none" id="encoder-cmds">
 113       <title>Encoder Commands</title>
 114       <tgroup cols="3">
 115         &cs-def;
 116         <tbody valign="top">
 117           <row>
 118             <entry><constant>V4L2_ENC_CMD_START</constant></entry>
 119             <entry>0</entry>
 120             <entry>Start the encoder. When the encoder is already
 121 running or paused, this command does nothing. No flags are defined for
 122 this command.</entry>
 123           </row>
 124           <row>
 125             <entry><constant>V4L2_ENC_CMD_STOP</constant></entry>
 126             <entry>1</entry>
 127             <entry>Stop the encoder. When the
 128 <constant>V4L2_ENC_CMD_STOP_AT_GOP_END</constant> flag is set,
 129 encoding will continue until the end of the current <wordasword>Group
 130 Of Pictures</wordasword>, otherwise encoding will stop immediately.
 131 When the encoder is already stopped, this command does
 132 nothing.</entry>
 133           </row>
 134           <row>
 135             <entry><constant>V4L2_ENC_CMD_PAUSE</constant></entry>
 136             <entry>2</entry>
 137             <entry>Pause the encoder. When the encoder has not been
 138 started yet, the driver will return an &EPERM;. When the encoder is
 139 already paused, this command does nothing. No flags are defined for
 140 this command.</entry>
 141           </row>
 142           <row>
 143             <entry><constant>V4L2_ENC_CMD_RESUME</constant></entry>
 144             <entry>3</entry>
 145             <entry>Resume encoding after a PAUSE command. When the
 146 encoder has not been started yet, the driver will return an &EPERM;.
 147 When the encoder is already running, this command does nothing. No
 148 flags are defined for this command.</entry>
 149           </row>
 150         </tbody>
 151       </tgroup>
 152     </table>
 153
 154     <table pgwide="1" frame="none" id="encoder-flags">
 155       <title>Encoder Command Flags</title>
 156       <tgroup cols="3">
 157         &cs-def;
 158         <tbody valign="top">
 159           <row>
 160             <entry><constant>V4L2_ENC_CMD_STOP_AT_GOP_END</constant></entry>
 161             <entry>0x0001</entry>
 162             <entry>Stop encoding at the end of the current <wordasword>Group Of
 163 Pictures</wordasword>, rather than immediately.</entry>
 164           </row>
 165        </tbody>
 166       </tgroup>
 167     </table>
 168   </refsect1>
 169
 170   <refsect1>
 171     &return-value;
 172
 173     <variablelist>
 174       <varlistentry>
 175         <term><errorcode>EINVAL</errorcode></term>
 176         <listitem>
 177           <para>The <structfield>cmd</structfield> field is invalid.</para>
 178         </listitem>
 179       </varlistentry>
 180       <varlistentry>
 181         <term><errorcode>EPERM</errorcode></term>
 182         <listitem>
 183           <para>The application sent a PAUSE or RESUME command when
 184 the encoder was not running.</para>
 185         </listitem>
 186       </varlistentry>
 187     </variablelist>
 188   </refsect1>
 189 </refentry>