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
54decoder, <constant>VIDIOC_TRY_DECODER_CMD</constant> can be used to
55try a command without actually executing it. To send a command applications
56must initialize all fields of a &v4l2-decoder-cmd; and call
57<constant>VIDIOC_DECODER_CMD</constant> or <constant>VIDIOC_TRY_DECODER_CMD</constant>
58with a pointer to this structure.</para>
59
60    <para>The <structfield>cmd</structfield> field must contain the
61command code. Some commands use the <structfield>flags</structfield> field for
62additional information.
63</para>
64
65    <para>A <function>write</function>() or &VIDIOC-STREAMON; call sends an implicit
66START 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
70file descriptor sends an implicit immediate STOP command to the decoder, and all
71buffered data is discarded.</para>
72
73    <para>These ioctls are optional, not all drivers may support
74them. 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
94this 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.
118Negative numbers denote reverse playback, so -1000 does reverse playback at normal
119speed. 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
121just 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
130application. Possible values are <constant>V4L2_DEC_START_FMT_NONE</constant> if
131there are no format restrictions or <constant>V4L2_DEC_START_FMT_GOP</constant>
132if the decoder operates on full GOPs (<wordasword>Group Of Pictures</wordasword>).
133This is usually the case for reverse playback: the decoder needs full GOPs, which
134it can then play in reverse order. So to implement reverse playback the application
135must 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
152if the playback is already past that timestamp. Leave to 0 if you want to stop after the
153last 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
169applications 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
184running or paused, this command will just change the playback speed.
185That means that calling <constant>V4L2_DEC_CMD_START</constant> when
186the decoder was paused will <emphasis>not</emphasis> resume the decoder.
187You have to explicitly call <constant>V4L2_DEC_CMD_RESUME</constant> for that.
188This command has one flag:
189<constant>V4L2_DEC_CMD_START_MUTE_AUDIO</constant>. If set, then audio will
190be 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,
197this command does nothing. This command has two flags:
198if <constant>V4L2_DEC_CMD_STOP_TO_BLACK</constant> is set, then the decoder will
199set the picture to black after it stopped decoding. Otherwise the last image will
200repeat. mem2mem decoders will stop producing new frames altogether. They will send
201a <constant>V4L2_EVENT_EOS</constant> event when the last frame has been decoded
202and 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
204capture queue to indicate there will be no new buffers produced to dequeue. This
205buffer 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,
209but return an &EPIPE;.
210If <constant>V4L2_DEC_CMD_STOP_IMMEDIATELY</constant> is set, then the decoder
211stops immediately (ignoring the <structfield>pts</structfield> value), otherwise it
212will keep decoding until timestamp >= pts or until the last of the pending data from
213its 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
220started yet, the driver will return an &EPERM;. When the decoder is
221already paused, this command does nothing. This command has one flag:
222if <constant>V4L2_DEC_CMD_PAUSE_TO_BLACK</constant> is set, then set the
223decoder 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
230decoder has not been started yet, the driver will return an &EPERM;.
231When the decoder is already running, this command does nothing. No
232flags 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
254the decoder was not running.</para>
255	</listitem>
256      </varlistentry>
257    </variablelist>
258  </refsect1>
259</refentry>
260