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