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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>
56interface 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
61decoder, <constant>VIDIOC_TRY_DECODER_CMD</constant> can be used to
62try a command without actually executing it. To send a command applications
63must initialize all fields of a &v4l2-decoder-cmd; and call
64<constant>VIDIOC_DECODER_CMD</constant> or <constant>VIDIOC_TRY_DECODER_CMD</constant>
65with a pointer to this structure.</para>
66
67 <para>The <structfield>cmd</structfield> field must contain the
68command code. Some commands use the <structfield>flags</structfield> field for
69additional information.
70</para>
71
72 <para>A <function>write</function>() or &VIDIOC-STREAMON; call sends an implicit
73START 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
77file descriptor sends an implicit immediate STOP command to the decoder, and all
78buffered data is discarded.</para>
79
80 <para>These ioctls are optional, not all drivers may support
81them. 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
101this 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.
125Negative numbers denote reverse playback, so -1000 does reverse playback at normal
126speed. 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
128just 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
137application. Possible values are <constant>V4L2_DEC_START_FMT_NONE</constant> if
138there are no format restrictions or <constant>V4L2_DEC_START_FMT_GOP</constant>
139if the decoder operates on full GOPs (<wordasword>Group Of Pictures</wordasword>).
140This is usually the case for reverse playback: the decoder needs full GOPs, which
141it can then play in reverse order. So to implement reverse playback the application
142must 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
159if the playback is already past that timestamp. Leave to 0 if you want to stop after the
160last 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
176applications 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
191running or paused, this command will just change the playback speed.
192That means that calling <constant>V4L2_DEC_CMD_START</constant> when
193the decoder was paused will <emphasis>not</emphasis> resume the decoder.
194You have to explicitly call <constant>V4L2_DEC_CMD_RESUME</constant> for that.
195This command has one flag:
196<constant>V4L2_DEC_CMD_START_MUTE_AUDIO</constant>. If set, then audio will
197be 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,
204this command does nothing. This command has two flags:
205if <constant>V4L2_DEC_CMD_STOP_TO_BLACK</constant> is set, then the decoder will
206set the picture to black after it stopped decoding. Otherwise the last image will
207repeat. If <constant>V4L2_DEC_CMD_STOP_IMMEDIATELY</constant> is set, then the decoder
208stops immediately (ignoring the <structfield>pts</structfield> value), otherwise it
209will keep decoding until timestamp >= pts or until the last of the pending data from
210its 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
217started yet, the driver will return an &EPERM;. When the decoder is
218already paused, this command does nothing. This command has one flag:
219if <constant>V4L2_DEC_CMD_PAUSE_TO_BLACK</constant> is set, then set the
220decoder 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
227decoder has not been started yet, the driver will return an &EPERM;.
228When the decoder is already running, this command does nothing. No
229flags 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
251the decoder was not running.</para>
252 </listitem>
253 </varlistentry>
254 </variablelist>
255 </refsect1>
256</refentry>