1<html><head><meta http-equiv="Content-Type" content="text/html; charset=ANSI_X3.4-1968"><title>ioctl VIDIOC_DECODER_CMD, VIDIOC_TRY_DECODER_CMD</title><meta name="generator" content="DocBook XSL Stylesheets V1.78.1"><link rel="home" href="index.html" title="LINUX MEDIA INFRASTRUCTURE API"><link rel="up" href="user-func.html" title="Appendix A. Function Reference"><link rel="prev" href="vidioc-dbg-g-register.html" title="ioctl VIDIOC_DBG_G_REGISTER, VIDIOC_DBG_S_REGISTER"><link rel="next" href="vidioc-dqevent.html" title="ioctl VIDIOC_DQEVENT"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">ioctl VIDIOC_DECODER_CMD, VIDIOC_TRY_DECODER_CMD</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="vidioc-dbg-g-register.html">Prev</a> </td><th width="60%" align="center">Appendix A. Function Reference</th><td width="20%" align="right"> <a accesskey="n" href="vidioc-dqevent.html">Next</a></td></tr></table><hr></div><div class="refentry"><a name="vidioc-decoder-cmd"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>VIDIOC_DECODER_CMD, VIDIOC_TRY_DECODER_CMD — Execute an decoder command</p></div><div class="refsynopsisdiv"><h2>Synopsis</h2><div class="funcsynopsis"><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">int <b class="fsfunc">ioctl</b>(</code></td><td>int <var class="pdparam">fd</var>, </td></tr><tr><td> </td><td>int <var class="pdparam">request</var>, </td></tr><tr><td> </td><td>struct v4l2_decoder_cmd *<var class="pdparam">argp</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div></div></div><div class="refsect1"><a name="idp1112239508"></a><h2>Arguments</h2><div class="variablelist"><dl class="variablelist"><dt><span class="term"><em class="parameter"><code>fd</code></em></span></dt><dd><p>File descriptor returned by <a class="link" href="func-open.html" title="V4L2 open()"><code class="function">open()</code></a>.</p></dd><dt><span class="term"><em class="parameter"><code>request</code></em></span></dt><dd><p>VIDIOC_DECODER_CMD, VIDIOC_TRY_DECODER_CMD</p></dd><dt><span class="term"><em class="parameter"><code>argp</code></em></span></dt><dd><p></p></dd></dl></div></div><div class="refsect1"><a name="idp1112243580"></a><h2>Description</h2><p>These ioctls control an audio/video (usually MPEG-) decoder. 2<code class="constant">VIDIOC_DECODER_CMD</code> sends a command to the 3decoder, <code class="constant">VIDIOC_TRY_DECODER_CMD</code> can be used to 4try a command without actually executing it. To send a command applications 5must initialize all fields of a struct <a class="link" href="vidioc-decoder-cmd.html#v4l2-decoder-cmd" title="Table A.10. struct v4l2_decoder_cmd">v4l2_decoder_cmd</a> and call 6<code class="constant">VIDIOC_DECODER_CMD</code> or <code class="constant">VIDIOC_TRY_DECODER_CMD</code> 7with a pointer to this structure.</p><p>The <em class="structfield"><code>cmd</code></em> field must contain the 8command code. Some commands use the <em class="structfield"><code>flags</code></em> field for 9additional information. 10</p><p>A <code class="function">write</code>() or <a class="link" href="vidioc-streamon.html" title="ioctl VIDIOC_STREAMON, VIDIOC_STREAMOFF"><code class="constant">VIDIOC_STREAMON</code></a> call sends an implicit 11START command to the decoder if it has not been started yet. 12</p><p>A <code class="function">close</code>() or <a class="link" href="vidioc-streamon.html" title="ioctl VIDIOC_STREAMON, VIDIOC_STREAMOFF"><code class="constant">VIDIOC_STREAMOFF</code></a> call of a streaming 13file descriptor sends an implicit immediate STOP command to the decoder, and all 14buffered data is discarded.</p><p>These ioctls are optional, not all drivers may support 15them. They were introduced in Linux 3.3.</p><div class="table"><a name="v4l2-decoder-cmd"></a><p class="title"><b>Table A.10. struct <span class="structname">v4l2_decoder_cmd</span></b></p><div class="table-contents"><table summary="struct v4l2_decoder_cmd" width="100%" border="0"><colgroup><col class="c1"><col class="c2"><col class="c3"><col><col></colgroup><tbody valign="top"><tr><td valign="top">__u32</td><td valign="top"><em class="structfield"><code>cmd</code></em></td><td valign="top"> </td><td valign="top"> </td><td valign="top">The decoder command, see <a class="xref" href="vidioc-decoder-cmd.html#decoder-cmds" title="Table A.11. Decoder Commands">Table A.11, “Decoder Commands”</a>.</td></tr><tr><td valign="top">__u32</td><td valign="top"><em class="structfield"><code>flags</code></em></td><td valign="top"> </td><td valign="top"> </td><td valign="top">Flags to go with the command. If no flags are defined for 16this command, drivers and applications must set this field to zero.</td></tr><tr><td valign="top">union</td><td valign="top">(anonymous)</td><td valign="top"> </td><td valign="top"> </td><td valign="top"> </td></tr><tr><td valign="top"> </td><td valign="top">struct</td><td valign="top"><em class="structfield"><code>start</code></em></td><td valign="top"> </td><td valign="top">Structure containing additional data for the 17<code class="constant">V4L2_DEC_CMD_START</code> command.</td></tr><tr><td valign="top"> </td><td valign="top"> </td><td valign="top">__s32</td><td valign="top"><em class="structfield"><code>speed</code></em></td><td valign="top">Playback speed and direction. The playback speed is defined as 18<em class="structfield"><code>speed</code></em>/1000 of the normal speed. So 1000 is normal playback. 19Negative numbers denote reverse playback, so -1000 does reverse playback at normal 20speed. Speeds -1, 0 and 1 have special meanings: speed 0 is shorthand for 1000 21(normal playback). A speed of 1 steps just one frame forward, a speed of -1 steps 22just one frame back. 23 </td></tr><tr><td valign="top"> </td><td valign="top"> </td><td valign="top">__u32</td><td valign="top"><em class="structfield"><code>format</code></em></td><td valign="top">Format restrictions. This field is set by the driver, not the 24application. Possible values are <code class="constant">V4L2_DEC_START_FMT_NONE</code> if 25there are no format restrictions or <code class="constant">V4L2_DEC_START_FMT_GOP</code> 26if the decoder operates on full GOPs (<em class="wordasword">Group Of Pictures</em>). 27This is usually the case for reverse playback: the decoder needs full GOPs, which 28it can then play in reverse order. So to implement reverse playback the application 29must feed the decoder the last GOP in the video file, then the GOP before that, etc. etc. 30 </td></tr><tr><td valign="top"> </td><td valign="top">struct</td><td valign="top"><em class="structfield"><code>stop</code></em></td><td valign="top"> </td><td valign="top">Structure containing additional data for the 31<code class="constant">V4L2_DEC_CMD_STOP</code> command.</td></tr><tr><td valign="top"> </td><td valign="top"> </td><td valign="top">__u64</td><td valign="top"><em class="structfield"><code>pts</code></em></td><td valign="top">Stop playback at this <em class="structfield"><code>pts</code></em> or immediately 32if the playback is already past that timestamp. Leave to 0 if you want to stop after the 33last frame was decoded. 34 </td></tr><tr><td valign="top"> </td><td valign="top">struct</td><td valign="top"><em class="structfield"><code>raw</code></em></td><td valign="top"> </td><td valign="top"> </td></tr><tr><td valign="top"> </td><td valign="top"> </td><td valign="top">__u32</td><td valign="top"><em class="structfield"><code>data</code></em>[16]</td><td valign="top">Reserved for future extensions. Drivers and 35applications must set the array to zero.</td></tr></tbody></table></div></div><br class="table-break"><div class="table"><a name="decoder-cmds"></a><p class="title"><b>Table A.11. Decoder Commands</b></p><div class="table-contents"><table summary="Decoder Commands" width="100%" border="0"><colgroup><col class="c1"><col class="c2"><col class="c3"></colgroup><tbody valign="top"><tr><td valign="top"><code class="constant">V4L2_DEC_CMD_START</code></td><td valign="top">0</td><td valign="top">Start the decoder. When the decoder is already 36running or paused, this command will just change the playback speed. 37That means that calling <code class="constant">V4L2_DEC_CMD_START</code> when 38the decoder was paused will <span class="emphasis"><em>not</em></span> resume the decoder. 39You have to explicitly call <code class="constant">V4L2_DEC_CMD_RESUME</code> for that. 40This command has one flag: 41<code class="constant">V4L2_DEC_CMD_START_MUTE_AUDIO</code>. If set, then audio will 42be muted when playing back at a non-standard speed. 43 </td></tr><tr><td valign="top"><code class="constant">V4L2_DEC_CMD_STOP</code></td><td valign="top">1</td><td valign="top">Stop the decoder. When the decoder is already stopped, 44this command does nothing. This command has two flags: 45if <code class="constant">V4L2_DEC_CMD_STOP_TO_BLACK</code> is set, then the decoder will 46set the picture to black after it stopped decoding. Otherwise the last image will 47repeat. If <code class="constant">V4L2_DEC_CMD_STOP_IMMEDIATELY</code> is set, then the decoder 48stops immediately (ignoring the <em class="structfield"><code>pts</code></em> value), otherwise it 49will keep decoding until timestamp >= pts or until the last of the pending data from 50its internal buffers was decoded. 51</td></tr><tr><td valign="top"><code class="constant">V4L2_DEC_CMD_PAUSE</code></td><td valign="top">2</td><td valign="top">Pause the decoder. When the decoder has not been 52started yet, the driver will return an <span class="errorcode">EPERM</span> error code. When the decoder is 53already paused, this command does nothing. This command has one flag: 54if <code class="constant">V4L2_DEC_CMD_PAUSE_TO_BLACK</code> is set, then set the 55decoder output to black when paused. 56</td></tr><tr><td valign="top"><code class="constant">V4L2_DEC_CMD_RESUME</code></td><td valign="top">3</td><td valign="top">Resume decoding after a PAUSE command. When the 57decoder has not been started yet, the driver will return an <span class="errorcode">EPERM</span> error code. 58When the decoder is already running, this command does nothing. No 59flags are defined for this command.</td></tr></tbody></table></div></div><br class="table-break"></div><div class="refsect1"><a name="idp1112277676"></a><h2>Return Value</h2><p>On success <span class="returnvalue">0</span> is returned, on error <span class="returnvalue">-1</span> and the <code class="varname">errno</code> variable is set appropriately. The generic error codes are described at the <a class="link" href="gen_errors.html#gen-errors" title="Table 19.1. Generic error codes">Generic Error Codes</a> chapter.</p><div class="variablelist"><dl class="variablelist"><dt><span class="term"><span class="errorcode">EINVAL</span></span></dt><dd><p>The <em class="structfield"><code>cmd</code></em> field is invalid.</p></dd><dt><span class="term"><span class="errorcode">EPERM</span></span></dt><dd><p>The application sent a PAUSE or RESUME command when 60the decoder was not running.</p></dd></dl></div></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="vidioc-dbg-g-register.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="user-func.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="vidioc-dqevent.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">ioctl VIDIOC_DBG_G_REGISTER, VIDIOC_DBG_S_REGISTER </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> ioctl VIDIOC_DQEVENT</td></tr></table></div></body></html> 61