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Based on kernel version 3.9. Page generated on 2013-05-02 23:04 EST.

1	<refentry id="vidioc-streamon">
2	  <refmeta>
3	    <refentrytitle>ioctl VIDIOC_STREAMON, VIDIOC_STREAMOFF</refentrytitle>
4	    &manvol;
5	  </refmeta>
6	
7	  <refnamediv>
8	    <refname>VIDIOC_STREAMON</refname>
9	    <refname>VIDIOC_STREAMOFF</refname>
10	    <refpurpose>Start or stop streaming I/O</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>const int *<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_STREAMON, VIDIOC_STREAMOFF</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>The <constant>VIDIOC_STREAMON</constant> and
53	<constant>VIDIOC_STREAMOFF</constant> ioctl start and stop the capture
54	or output process during streaming (<link linkend="mmap">memory
55	mapping</link> or <link linkend="userp">user pointer</link>) I/O.</para>
56	
57	    <para>Specifically the capture hardware is disabled and no input
58	buffers are filled (if there are any empty buffers in the incoming
59	queue) until <constant>VIDIOC_STREAMON</constant> has been called.
60	Accordingly the output hardware is disabled, no video signal is
61	produced until <constant>VIDIOC_STREAMON</constant> has been called.
62	The ioctl will succeed only when at least one output buffer is in the
63	incoming queue.</para>
64	
65	    <para>The <constant>VIDIOC_STREAMOFF</constant> ioctl, apart of
66	aborting or finishing any DMA in progress, unlocks any user pointer
67	buffers locked in physical memory, and it removes all buffers from the
68	incoming and outgoing queues. That means all images captured but not
69	dequeued yet will be lost, likewise all images enqueued for output but
70	not transmitted yet. I/O returns to the same state as after calling
71	&VIDIOC-REQBUFS; and can be restarted accordingly.</para>
72	
73	    <para>Both ioctls take a pointer to an integer, the desired buffer or
74	stream type. This is the same as &v4l2-requestbuffers;
75	<structfield>type</structfield>.</para>
76	
77	    <para>If <constant>VIDIOC_STREAMON</constant> is called when streaming
78	is already in progress, or if <constant>VIDIOC_STREAMOFF</constant> is called
79	when streaming is already stopped, then the ioctl does nothing and 0 is
80	returned.</para>
81	
82	    <para>Note that applications can be preempted for unknown periods right
83	before or after the <constant>VIDIOC_STREAMON</constant> or
84	<constant>VIDIOC_STREAMOFF</constant> calls, there is no notion of
85	starting or stopping "now". Buffer timestamps can be used to
86	synchronize with other events.</para>
87	  </refsect1>
88	
89	  <refsect1>
90	    &return-value;
91	
92	    <variablelist>
93	      <varlistentry>
94		<term><errorcode>EINVAL</errorcode></term>
95		<listitem>
96		  <para>The buffer<structfield>type</structfield> is not supported,
97		  or no buffers have been allocated (memory mapping) or enqueued
98		  (output) yet.</para>
99		</listitem>
100	      </varlistentry>
101	      <varlistentry>
102		<term><errorcode>EPIPE</errorcode></term>
103		<listitem>
104		  <para>The driver implements <link
105		  linkend="pad-level-formats">pad-level format configuration</link> and
106		  the pipeline configuration is invalid.
107		  </para>
108		</listitem>
109	      </varlistentry>
110	    </variablelist>
111	  </refsect1>
112	</refentry>
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