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-<refentry id="vidioc-streamon">
- <refmeta>
- <refentrytitle>ioctl VIDIOC_STREAMON, VIDIOC_STREAMOFF</refentrytitle>
- &manvol;
- </refmeta>
-
- <refnamediv>
- <refname>VIDIOC_STREAMON</refname>
- <refname>VIDIOC_STREAMOFF</refname>
- <refpurpose>Start or stop streaming I/O</refpurpose>
- </refnamediv>
-
- <refsynopsisdiv>
- <funcsynopsis>
- <funcprototype>
- <funcdef>int <function>ioctl</function></funcdef>
- <paramdef>int <parameter>fd</parameter></paramdef>
- <paramdef>int <parameter>request</parameter></paramdef>
- <paramdef>const int *<parameter>argp</parameter></paramdef>
- </funcprototype>
- </funcsynopsis>
- </refsynopsisdiv>
-
- <refsect1>
- <title>Arguments</title>
-
- <variablelist>
- <varlistentry>
- <term><parameter>fd</parameter></term>
- <listitem>
- <para>&fd;</para>
- </listitem>
- </varlistentry>
- <varlistentry>
- <term><parameter>request</parameter></term>
- <listitem>
- <para>VIDIOC_STREAMON, VIDIOC_STREAMOFF</para>
- </listitem>
- </varlistentry>
- <varlistentry>
- <term><parameter>argp</parameter></term>
- <listitem>
- <para></para>
- </listitem>
- </varlistentry>
- </variablelist>
- </refsect1>
-
- <refsect1>
- <title>Description</title>
-
- <para>The <constant>VIDIOC_STREAMON</constant> and
-<constant>VIDIOC_STREAMOFF</constant> ioctl start and stop the capture
-or output process during streaming (<link linkend="mmap">memory
-mapping</link>, <link linkend="userp">user pointer</link> or
-<link linkend="dmabuf">DMABUF</link>) I/O.</para>
-
- <para>Capture hardware is disabled and no input
-buffers are filled (if there are any empty buffers in the incoming
-queue) until <constant>VIDIOC_STREAMON</constant> has been called.
-Output hardware is disabled and no video signal is
-produced until <constant>VIDIOC_STREAMON</constant> has been called.
-The ioctl will succeed when at least one output buffer is in the
-incoming queue.</para>
-
- <para>Memory-to-memory devices will not start until
-<constant>VIDIOC_STREAMON</constant> has been called for both the capture
-and output stream types.</para>
-
- <para>If <constant>VIDIOC_STREAMON</constant> fails then any already
-queued buffers will remain queued.</para>
-
- <para>The <constant>VIDIOC_STREAMOFF</constant> ioctl, apart of
-aborting or finishing any DMA in progress, unlocks any user pointer
-buffers locked in physical memory, and it removes all buffers from the
-incoming and outgoing queues. That means all images captured but not
-dequeued yet will be lost, likewise all images enqueued for output but
-not transmitted yet. I/O returns to the same state as after calling
-&VIDIOC-REQBUFS; and can be restarted accordingly.</para>
-
- <para>If buffers have been queued with &VIDIOC-QBUF; and
-<constant>VIDIOC_STREAMOFF</constant> is called without ever having
-called <constant>VIDIOC_STREAMON</constant>, then those queued buffers
-will also be removed from the incoming queue and all are returned to the
-same state as after calling &VIDIOC-REQBUFS; and can be restarted
-accordingly.</para>
-
- <para>Both ioctls take a pointer to an integer, the desired buffer or
-stream type. This is the same as &v4l2-requestbuffers;
-<structfield>type</structfield>.</para>
-
- <para>If <constant>VIDIOC_STREAMON</constant> is called when streaming
-is already in progress, or if <constant>VIDIOC_STREAMOFF</constant> is called
-when streaming is already stopped, then 0 is returned. Nothing happens in the
-case of <constant>VIDIOC_STREAMON</constant>, but <constant>VIDIOC_STREAMOFF</constant>
-will return queued buffers to their starting state as mentioned above.</para>
-
- <para>Note that applications can be preempted for unknown periods right
-before or after the <constant>VIDIOC_STREAMON</constant> or
-<constant>VIDIOC_STREAMOFF</constant> calls, there is no notion of
-starting or stopping "now". Buffer timestamps can be used to
-synchronize with other events.</para>
- </refsect1>
-
- <refsect1>
- &return-value;
-
- <variablelist>
- <varlistentry>
- <term><errorcode>EINVAL</errorcode></term>
- <listitem>
- <para>The buffer <structfield>type</structfield> is not supported,
- or no buffers have been allocated (memory mapping) or enqueued
- (output) yet.</para>
- </listitem>
- </varlistentry>
- <varlistentry>
- <term><errorcode>EPIPE</errorcode></term>
- <listitem>
- <para>The driver implements <link
- linkend="pad-level-formats">pad-level format configuration</link> and
- the pipeline configuration is invalid.
- </para>
- </listitem>
- </varlistentry>
- <varlistentry>
- <term><errorcode>ENOLINK</errorcode></term>
- <listitem>
- <para>The driver implements Media Controller interface and
- the pipeline link configuration is invalid.
- </para>
- </listitem>
- </varlistentry>
- </variablelist>
- </refsect1>
-</refentry>