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Based on kernel version 3.15.4. Page generated on 2014-07-07 09:02 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>, <link linkend="userp">user pointer</link> or
56	<link linkend="dmabuf">DMABUF</link>) I/O.</para>
57	
58	    <para>Capture hardware is disabled and no input
59	buffers are filled (if there are any empty buffers in the incoming
60	queue) until <constant>VIDIOC_STREAMON</constant> has been called.
61	Output hardware is disabled and no video signal is
62	produced until <constant>VIDIOC_STREAMON</constant> has been called.
63	The ioctl will succeed when at least one output buffer is in the
64	incoming queue.</para>
65	
66	    <para>Memory-to-memory devices will not start until
67	<constant>VIDIOC_STREAMON</constant> has been called for both the capture
68	and output stream types.</para>
69	
70	    <para>If <constant>VIDIOC_STREAMON</constant> fails then any already
71	queued buffers will remain queued.</para>
72	
73	    <para>The <constant>VIDIOC_STREAMOFF</constant> ioctl, apart of
74	aborting or finishing any DMA in progress, unlocks any user pointer
75	buffers locked in physical memory, and it removes all buffers from the
76	incoming and outgoing queues. That means all images captured but not
77	dequeued yet will be lost, likewise all images enqueued for output but
78	not transmitted yet. I/O returns to the same state as after calling
79	&VIDIOC-REQBUFS; and can be restarted accordingly.</para>
80	
81	    <para>If buffers have been queued with &VIDIOC-QBUF; and
82	<constant>VIDIOC_STREAMOFF</constant> is called without ever having
83	called <constant>VIDIOC_STREAMON</constant>, then those queued buffers
84	will also be removed from the incoming queue and all are returned to the
85	same state as after calling &VIDIOC-REQBUFS; and can be restarted
86	accordingly.</para>
87	
88	    <para>Both ioctls take a pointer to an integer, the desired buffer or
89	stream type. This is the same as &v4l2-requestbuffers;
90	<structfield>type</structfield>.</para>
91	
92	    <para>If <constant>VIDIOC_STREAMON</constant> is called when streaming
93	is already in progress, or if <constant>VIDIOC_STREAMOFF</constant> is called
94	when streaming is already stopped, then 0 is returned. Nothing happens in the
95	case of <constant>VIDIOC_STREAMON</constant>, but <constant>VIDIOC_STREAMOFF</constant>
96	will return queued buffers to their starting state as mentioned above.</para>
97	
98	    <para>Note that applications can be preempted for unknown periods right
99	before or after the <constant>VIDIOC_STREAMON</constant> or
100	<constant>VIDIOC_STREAMOFF</constant> calls, there is no notion of
101	starting or stopping "now". Buffer timestamps can be used to
102	synchronize with other events.</para>
103	  </refsect1>
104	
105	  <refsect1>
106	    &return-value;
107	
108	    <variablelist>
109	      <varlistentry>
110		<term><errorcode>EINVAL</errorcode></term>
111		<listitem>
112		  <para>The buffer <structfield>type</structfield> is not supported,
113		  or no buffers have been allocated (memory mapping) or enqueued
114		  (output) yet.</para>
115		</listitem>
116	      </varlistentry>
117	      <varlistentry>
118		<term><errorcode>EPIPE</errorcode></term>
119		<listitem>
120		  <para>The driver implements <link
121		  linkend="pad-level-formats">pad-level format configuration</link> and
122		  the pipeline configuration is invalid.
123		  </para>
124		</listitem>
125	      </varlistentry>
126	    </variablelist>
127	  </refsect1>
128	</refentry>
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