1<refentry id="vidioc-encoder-cmd">
2  <refmeta>
3    <refentrytitle>ioctl VIDIOC_ENCODER_CMD, VIDIOC_TRY_ENCODER_CMD</refentrytitle>
4    &manvol;
5  </refmeta>
6
7  <refnamediv>
8    <refname>VIDIOC_ENCODER_CMD</refname>
9    <refname>VIDIOC_TRY_ENCODER_CMD</refname>
10    <refpurpose>Execute an encoder 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_encoder_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_ENCODER_CMD, VIDIOC_TRY_ENCODER_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-) encoder.
60<constant>VIDIOC_ENCODER_CMD</constant> sends a command to the
61encoder, <constant>VIDIOC_TRY_ENCODER_CMD</constant> can be used to
62try a command without actually executing it.</para>
63
64    <para>To send a command applications must initialize all fields of a
65    &v4l2-encoder-cmd; and call
66    <constant>VIDIOC_ENCODER_CMD</constant> or
67    <constant>VIDIOC_TRY_ENCODER_CMD</constant> with a pointer to this
68    structure.</para>
69
70    <para>The <structfield>cmd</structfield> field must contain the
71command code. The <structfield>flags</structfield> field is currently
72only used by the STOP command and contains one bit: If the
73<constant>V4L2_ENC_CMD_STOP_AT_GOP_END</constant> flag is set,
74encoding will continue until the end of the current <wordasword>Group
75Of Pictures</wordasword>, otherwise it will stop immediately.</para>
76
77    <para>A <function>read</function>() call sends a START command to
78the encoder if it has not been started yet. After a STOP command,
79<function>read</function>() calls will read the remaining data
80buffered by the driver. When the buffer is empty,
81<function>read</function>() will return zero and the next
82<function>read</function>() call will restart the encoder.</para>
83
84    <para>A <function>close</function>() call sends an immediate STOP
85to the encoder, and all buffered data is discarded.</para>
86
87    <para>These ioctls are optional, not all drivers may support
88them. They were introduced in Linux 2.6.21.</para>
89
90    <table pgwide="1" frame="none" id="v4l2-encoder-cmd">
91      <title>struct <structname>v4l2_encoder_cmd</structname></title>
92      <tgroup cols="3">
93	&cs-str;
94	<tbody valign="top">
95	  <row>
96	    <entry>__u32</entry>
97	    <entry><structfield>cmd</structfield></entry>
98	    <entry>The encoder command, see <xref linkend="encoder-cmds" />.</entry>
99	  </row>
100	  <row>
101	    <entry>__u32</entry>
102	    <entry><structfield>flags</structfield></entry>
103	    <entry>Flags to go with the command, see <xref
104		linkend="encoder-flags" />. If no flags are defined for
105this command, drivers and applications must set this field to
106zero.</entry>
107	  </row>
108	  <row>
109	    <entry>__u32</entry>
110	    <entry><structfield>data</structfield>[8]</entry>
111	    <entry>Reserved for future extensions. Drivers and
112applications must set the array to zero.</entry>
113	  </row>
114	</tbody>
115      </tgroup>
116    </table>
117
118    <table pgwide="1" frame="none" id="encoder-cmds">
119      <title>Encoder Commands</title>
120      <tgroup cols="3">
121	&cs-def;
122	<tbody valign="top">
123	  <row>
124	    <entry><constant>V4L2_ENC_CMD_START</constant></entry>
125	    <entry>0</entry>
126	    <entry>Start the encoder. When the encoder is already
127running or paused, this command does nothing. No flags are defined for
128this command.</entry>
129	  </row>
130	  <row>
131	    <entry><constant>V4L2_ENC_CMD_STOP</constant></entry>
132	    <entry>1</entry>
133	    <entry>Stop the encoder. When the
134<constant>V4L2_ENC_CMD_STOP_AT_GOP_END</constant> flag is set,
135encoding will continue until the end of the current <wordasword>Group
136Of Pictures</wordasword>, otherwise encoding will stop immediately.
137When the encoder is already stopped, this command does
138nothing.</entry>
139	  </row>
140	  <row>
141	    <entry><constant>V4L2_ENC_CMD_PAUSE</constant></entry>
142	    <entry>2</entry>
143	    <entry>Pause the encoder. When the encoder has not been
144started yet, the driver will return an &EPERM;. When the encoder is
145already paused, this command does nothing. No flags are defined for
146this command.</entry>
147	  </row>
148	  <row>
149	    <entry><constant>V4L2_ENC_CMD_RESUME</constant></entry>
150	    <entry>3</entry>
151	    <entry>Resume encoding after a PAUSE command. When the
152encoder has not been started yet, the driver will return an &EPERM;.
153When the encoder is already running, this command does nothing. No
154flags are defined for this command.</entry>
155	  </row>
156	</tbody>
157      </tgroup>
158    </table>
159
160    <table pgwide="1" frame="none" id="encoder-flags">
161      <title>Encoder Command Flags</title>
162      <tgroup cols="3">
163	&cs-def;
164	<tbody valign="top">
165	  <row>
166	    <entry><constant>V4L2_ENC_CMD_STOP_AT_GOP_END</constant></entry>
167	    <entry>0x0001</entry>
168	    <entry>Stop encoding at the end of the current <wordasword>Group Of
169Pictures</wordasword>, rather than immediately.</entry>
170	  </row>
171       </tbody>
172      </tgroup>
173    </table>
174  </refsect1>
175
176  <refsect1>
177    &return-value;
178
179    <variablelist>
180      <varlistentry>
181	<term><errorcode>EINVAL</errorcode></term>
182	<listitem>
183	  <para>The <structfield>cmd</structfield> field is invalid.</para>
184	</listitem>
185      </varlistentry>
186      <varlistentry>
187	<term><errorcode>EPERM</errorcode></term>
188	<listitem>
189	  <para>The application sent a PAUSE or RESUME command when
190the encoder was not running.</para>
191	</listitem>
192      </varlistentry>
193    </variablelist>
194  </refsect1>
195</refentry>
196