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

   1 <refentry id="vidioc-decoder-cmd">
   2   <refmeta>
   3     <refentrytitle>ioctl VIDIOC_DECODER_CMD, VIDIOC_TRY_DECODER_CMD</refentrytitle>
   4     &manvol;
   5   </refmeta>
   6
   7   <refnamediv>
   8     <refname>VIDIOC_DECODER_CMD</refname>
   9     <refname>VIDIOC_TRY_DECODER_CMD</refname>
  10     <refpurpose>Execute an decoder 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_decoder_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_DECODER_CMD, VIDIOC_TRY_DECODER_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-) decoder.
  53 <constant>VIDIOC_DECODER_CMD</constant> sends a command to the
  54 decoder, <constant>VIDIOC_TRY_DECODER_CMD</constant> can be used to
  55 try a command without actually executing it. To send a command applications
  56 must initialize all fields of a &v4l2-decoder-cmd; and call
  57 <constant>VIDIOC_DECODER_CMD</constant> or <constant>VIDIOC_TRY_DECODER_CMD</constant>
  58 with a pointer to this structure.</para>
  59
  60     <para>The <structfield>cmd</structfield> field must contain the
  61 command code. Some commands use the <structfield>flags</structfield> field for
  62 additional information.
  63 </para>
  64
  65     <para>A <function>write</function>() or &VIDIOC-STREAMON; call sends an implicit
  66 START command to the decoder if it has not been started yet.
  67 </para>
  68
  69     <para>A <function>close</function>() or &VIDIOC-STREAMOFF; call of a streaming
  70 file descriptor sends an implicit immediate STOP command to the decoder, and all
  71 buffered data is discarded.</para>
  72
  73     <para>These ioctls are optional, not all drivers may support
  74 them. They were introduced in Linux 3.3.</para>
  75
  76     <table pgwide="1" frame="none" id="v4l2-decoder-cmd">
  77       <title>struct <structname>v4l2_decoder_cmd</structname></title>
  78       <tgroup cols="5">
  79         &cs-str;
  80         <tbody valign="top">
  81           <row>
  82             <entry>__u32</entry>
  83             <entry><structfield>cmd</structfield></entry>
  84             <entry></entry>
  85             <entry></entry>
  86             <entry>The decoder command, see <xref linkend="decoder-cmds" />.</entry>
  87           </row>
  88           <row>
  89             <entry>__u32</entry>
  90             <entry><structfield>flags</structfield></entry>
  91             <entry></entry>
  92             <entry></entry>
  93             <entry>Flags to go with the command. If no flags are defined for
  94 this command, drivers and applications must set this field to zero.</entry>
  95           </row>
  96           <row>
  97             <entry>union</entry>
  98             <entry>(anonymous)</entry>
  99             <entry></entry>
 100             <entry></entry>
 101             <entry></entry>
 102           </row>
 103           <row>
 104             <entry></entry>
 105             <entry>struct</entry>
 106             <entry><structfield>start</structfield></entry>
 107             <entry></entry>
 108             <entry>Structure containing additional data for the
 109 <constant>V4L2_DEC_CMD_START</constant> command.</entry>
 110           </row>
 111           <row>
 112             <entry></entry>
 113             <entry></entry>
 114             <entry>__s32</entry>
 115             <entry><structfield>speed</structfield></entry>
 116             <entry>Playback speed and direction. The playback speed is defined as
 117 <structfield>speed</structfield>/1000 of the normal speed. So 1000 is normal playback.
 118 Negative numbers denote reverse playback, so -1000 does reverse playback at normal
 119 speed. Speeds -1, 0 and 1 have special meanings: speed 0 is shorthand for 1000
 120 (normal playback). A speed of 1 steps just one frame forward, a speed of -1 steps
 121 just one frame back.
 122             </entry>
 123           </row>
 124           <row>
 125             <entry></entry>
 126             <entry></entry>
 127             <entry>__u32</entry>
 128             <entry><structfield>format</structfield></entry>
 129             <entry>Format restrictions. This field is set by the driver, not the
 130 application. Possible values are <constant>V4L2_DEC_START_FMT_NONE</constant> if
 131 there are no format restrictions or <constant>V4L2_DEC_START_FMT_GOP</constant>
 132 if the decoder operates on full GOPs (<wordasword>Group Of Pictures</wordasword>).
 133 This is usually the case for reverse playback: the decoder needs full GOPs, which
 134 it can then play in reverse order. So to implement reverse playback the application
 135 must feed the decoder the last GOP in the video file, then the GOP before that, etc. etc.
 136             </entry>
 137           </row>
 138           <row>
 139             <entry></entry>
 140             <entry>struct</entry>
 141             <entry><structfield>stop</structfield></entry>
 142             <entry></entry>
 143             <entry>Structure containing additional data for the
 144 <constant>V4L2_DEC_CMD_STOP</constant> command.</entry>
 145           </row>
 146           <row>
 147             <entry></entry>
 148             <entry></entry>
 149             <entry>__u64</entry>
 150             <entry><structfield>pts</structfield></entry>
 151             <entry>Stop playback at this <structfield>pts</structfield> or immediately
 152 if the playback is already past that timestamp. Leave to 0 if you want to stop after the
 153 last frame was decoded.
 154             </entry>
 155           </row>
 156           <row>
 157             <entry></entry>
 158             <entry>struct</entry>
 159             <entry><structfield>raw</structfield></entry>
 160             <entry></entry>
 161             <entry></entry>
 162           </row>
 163           <row>
 164             <entry></entry>
 165             <entry></entry>
 166             <entry>__u32</entry>
 167             <entry><structfield>data</structfield>[16]</entry>
 168             <entry>Reserved for future extensions. Drivers and
 169 applications must set the array to zero.</entry>
 170           </row>
 171         </tbody>
 172       </tgroup>
 173     </table>
 174
 175     <table pgwide="1" frame="none" id="decoder-cmds">
 176       <title>Decoder Commands</title>
 177       <tgroup cols="3">
 178         &cs-def;
 179         <tbody valign="top">
 180           <row>
 181             <entry><constant>V4L2_DEC_CMD_START</constant></entry>
 182             <entry>0</entry>
 183             <entry>Start the decoder. When the decoder is already
 184 running or paused, this command will just change the playback speed.
 185 That means that calling <constant>V4L2_DEC_CMD_START</constant> when
 186 the decoder was paused will <emphasis>not</emphasis> resume the decoder.
 187 You have to explicitly call <constant>V4L2_DEC_CMD_RESUME</constant> for that.
 188 This command has one flag:
 189 <constant>V4L2_DEC_CMD_START_MUTE_AUDIO</constant>. If set, then audio will
 190 be muted when playing back at a non-standard speed.
 191             </entry>
 192           </row>
 193           <row>
 194             <entry><constant>V4L2_DEC_CMD_STOP</constant></entry>
 195             <entry>1</entry>
 196             <entry>Stop the decoder. When the decoder is already stopped,
 197 this command does nothing. This command has two flags:
 198 if <constant>V4L2_DEC_CMD_STOP_TO_BLACK</constant> is set, then the decoder will
 199 set the picture to black after it stopped decoding. Otherwise the last image will
 200 repeat. mem2mem decoders will stop producing new frames altogether. They will send
 201 a <constant>V4L2_EVENT_EOS</constant> event when the last frame has been decoded
 202 and all frames are ready to be dequeued and will set the
 203 <constant>V4L2_BUF_FLAG_LAST</constant> buffer flag on the last buffer of the
 204 capture queue to indicate there will be no new buffers produced to dequeue. This
 205 buffer may be empty, indicated by the driver setting the
 206 <structfield>bytesused</structfield> field to 0. Once the
 207 <constant>V4L2_BUF_FLAG_LAST</constant> flag was set, the
 208 <link linkend="vidioc-qbuf">VIDIOC_DQBUF</link> ioctl will not block anymore,
 209 but return an &EPIPE;.
 210 If <constant>V4L2_DEC_CMD_STOP_IMMEDIATELY</constant> is set, then the decoder
 211 stops immediately (ignoring the <structfield>pts</structfield> value), otherwise it
 212 will keep decoding until timestamp >= pts or until the last of the pending data from
 213 its internal buffers was decoded.
 214 </entry>
 215           </row>
 216           <row>
 217             <entry><constant>V4L2_DEC_CMD_PAUSE</constant></entry>
 218             <entry>2</entry>
 219             <entry>Pause the decoder. When the decoder has not been
 220 started yet, the driver will return an &EPERM;. When the decoder is
 221 already paused, this command does nothing. This command has one flag:
 222 if <constant>V4L2_DEC_CMD_PAUSE_TO_BLACK</constant> is set, then set the
 223 decoder output to black when paused.
 224 </entry>
 225           </row>
 226           <row>
 227             <entry><constant>V4L2_DEC_CMD_RESUME</constant></entry>
 228             <entry>3</entry>
 229             <entry>Resume decoding after a PAUSE command. When the
 230 decoder has not been started yet, the driver will return an &EPERM;.
 231 When the decoder is already running, this command does nothing. No
 232 flags are defined for this command.</entry>
 233           </row>
 234         </tbody>
 235       </tgroup>
 236     </table>
 237
 238   </refsect1>
 239
 240   <refsect1>
 241     &return-value;
 242
 243     <variablelist>
 244       <varlistentry>
 245         <term><errorcode>EINVAL</errorcode></term>
 246         <listitem>
 247           <para>The <structfield>cmd</structfield> field is invalid.</para>
 248         </listitem>
 249       </varlistentry>
 250       <varlistentry>
 251         <term><errorcode>EPERM</errorcode></term>
 252         <listitem>
 253           <para>The application sent a PAUSE or RESUME command when
 254 the decoder was not running.</para>
 255         </listitem>
 256       </varlistentry>
 257     </variablelist>
 258   </refsect1>
 259 </refentry>