Documentation/DocBook/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     <note>
  53       <title>Experimental</title>
  54
  55       <para>This is an <link linkend="experimental">experimental</link>
  56 interface and may change in the future.</para>
  57     </note>
  58
  59     <para>These ioctls control an audio/video (usually MPEG-) encoder.
  60 <constant>VIDIOC_ENCODER_CMD</constant> sends a command to the
  61 encoder, <constant>VIDIOC_TRY_ENCODER_CMD</constant> can be used to
  62 try a command without actually executing it.</para>
  63
  64     <para>To send a command applications must initialize all fields of a
  65     &v4l2-encoder-cmd; and call
  66     <constant>VIDIOC_ENCODER_CMD</constant> or
  67     <constant>VIDIOC_TRY_ENCODER_CMD</constant> with a pointer to this
  68     structure.</para>
  69
  70     <para>The <structfield>cmd</structfield> field must contain the
  71 command code. The <structfield>flags</structfield> field is currently
  72 only used by the STOP command and contains one bit: If the
  73 <constant>V4L2_ENC_CMD_STOP_AT_GOP_END</constant> flag is set,
  74 encoding will continue until the end of the current <wordasword>Group
  75 Of Pictures</wordasword>, otherwise it will stop immediately.</para>
  76
  77     <para>A <function>read</function>() call sends a START command to
  78 the encoder if it has not been started yet. After a STOP command,
  79 <function>read</function>() calls will read the remaining data
  80 buffered by the driver. When the buffer is empty,
  81 <function>read</function>() will return zero and the next
  82 <function>read</function>() call will restart the encoder.</para>
  83
  84     <para>A <function>close</function>() call sends an immediate STOP
  85 to the encoder, and all buffered data is discarded.</para>
  86
  87     <para>These ioctls are optional, not all drivers may support
  88 them. They were introduced in Linux 2.6.21.</para>
  89
  90     <table pgwide="1" frame="none" id="v4l2-encoder-cmd">
  91       <title>struct <structname>v4l2_encoder_cmd</structname></title>
  92       <tgroup cols="3">
  93         &cs-str;
  94         <tbody valign="top">
  95           <row>
  96             <entry>__u32</entry>
  97             <entry><structfield>cmd</structfield></entry>
  98             <entry>The encoder command, see <xref linkend="encoder-cmds" />.</entry>
  99           </row>
 100           <row>
 101             <entry>__u32</entry>
 102             <entry><structfield>flags</structfield></entry>
 103             <entry>Flags to go with the command, see <xref
 104                 linkend="encoder-flags" />. If no flags are defined for
 105 this command, drivers and applications must set this field to
 106 zero.</entry>
 107           </row>
 108           <row>
 109             <entry>__u32</entry>
 110             <entry><structfield>data</structfield>[8]</entry>
 111             <entry>Reserved for future extensions. Drivers and
 112 applications must set the array to zero.</entry>
 113           </row>
 114         </tbody>
 115       </tgroup>
 116     </table>
 117
 118     <table pgwide="1" frame="none" id="encoder-cmds">
 119       <title>Encoder Commands</title>
 120       <tgroup cols="3">
 121         &cs-def;
 122         <tbody valign="top">
 123           <row>
 124             <entry><constant>V4L2_ENC_CMD_START</constant></entry>
 125             <entry>0</entry>
 126             <entry>Start the encoder. When the encoder is already
 127 running or paused, this command does nothing. No flags are defined for
 128 this command.</entry>
 129           </row>
 130           <row>
 131             <entry><constant>V4L2_ENC_CMD_STOP</constant></entry>
 132             <entry>1</entry>
 133             <entry>Stop the encoder. When the
 134 <constant>V4L2_ENC_CMD_STOP_AT_GOP_END</constant> flag is set,
 135 encoding will continue until the end of the current <wordasword>Group
 136 Of Pictures</wordasword>, otherwise encoding will stop immediately.
 137 When the encoder is already stopped, this command does
 138 nothing.</entry>
 139           </row>
 140           <row>
 141             <entry><constant>V4L2_ENC_CMD_PAUSE</constant></entry>
 142             <entry>2</entry>
 143             <entry>Pause the encoder. When the encoder has not been
 144 started yet, the driver will return an &EPERM;. When the encoder is
 145 already paused, this command does nothing. No flags are defined for
 146 this command.</entry>
 147           </row>
 148           <row>
 149             <entry><constant>V4L2_ENC_CMD_RESUME</constant></entry>
 150             <entry>3</entry>
 151             <entry>Resume encoding after a PAUSE command. When the
 152 encoder has not been started yet, the driver will return an &EPERM;.
 153 When the encoder is already running, this command does nothing. No
 154 flags are defined for this command.</entry>
 155           </row>
 156         </tbody>
 157       </tgroup>
 158     </table>
 159
 160     <table pgwide="1" frame="none" id="encoder-flags">
 161       <title>Encoder Command Flags</title>
 162       <tgroup cols="3">
 163         &cs-def;
 164         <tbody valign="top">
 165           <row>
 166             <entry><constant>V4L2_ENC_CMD_STOP_AT_GOP_END</constant></entry>
 167             <entry>0x0001</entry>
 168             <entry>Stop encoding at the end of the current <wordasword>Group Of
 169 Pictures</wordasword>, rather than immediately.</entry>
 170           </row>
 171        </tbody>
 172       </tgroup>
 173     </table>
 174   </refsect1>
 175
 176   <refsect1>
 177     &return-value;
 178
 179     <variablelist>
 180       <varlistentry>
 181         <term><errorcode>EINVAL</errorcode></term>
 182         <listitem>
 183           <para>The driver does not support this ioctl, or the
 184 <structfield>cmd</structfield> field is invalid.</para>
 185         </listitem>
 186       </varlistentry>
 187       <varlistentry>
 188         <term><errorcode>EPERM</errorcode></term>
 189         <listitem>
 190           <para>The application sent a PAUSE or RESUME command when
 191 the encoder was not running.</para>
 192         </listitem>
 193       </varlistentry>
 194     </variablelist>
 195   </refsect1>
 196 </refentry>
 197
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