1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
2.. c:namespace:: V4L
3
4.. _VIDIOC_STREAMON:
5
6***************************************
7ioctl VIDIOC_STREAMON, VIDIOC_STREAMOFF
8***************************************
9
10Name
11====
12
13VIDIOC_STREAMON - VIDIOC_STREAMOFF - Start or stop streaming I/O
14
15Synopsis
16========
17
18.. c:macro:: VIDIOC_STREAMON
19
20``int ioctl(int fd, VIDIOC_STREAMON, const int *argp)``
21
22.. c:macro:: VIDIOC_STREAMOFF
23
24``int ioctl(int fd, VIDIOC_STREAMOFF, const int *argp)``
25
26Arguments
27=========
28
29``fd``
30    File descriptor returned by :c:func:`open()`.
31
32``argp``
33    Pointer to an integer.
34
35Description
36===========
37
38The ``VIDIOC_STREAMON`` and ``VIDIOC_STREAMOFF`` ioctl start and stop
39the capture or output process during streaming
40(:ref:`memory mapping <mmap>`, :ref:`user pointer <userp>` or
41:ref:`DMABUF <dmabuf>`) I/O.
42
43Capture hardware is disabled and no input buffers are filled (if there
44are any empty buffers in the incoming queue) until ``VIDIOC_STREAMON``
45has been called. Output hardware is disabled and no video signal is
46produced until ``VIDIOC_STREAMON`` has been called.
47
48Memory-to-memory devices will not start until ``VIDIOC_STREAMON`` has
49been called for both the capture and output stream types.
50
51If ``VIDIOC_STREAMON`` fails then any already queued buffers will remain
52queued.
53
54The ``VIDIOC_STREAMOFF`` ioctl, apart of aborting or finishing any DMA
55in progress, unlocks any user pointer buffers locked in physical memory,
56and it removes all buffers from the incoming and outgoing queues. That
57means all images captured but not dequeued yet will be lost, likewise
58all images enqueued for output but not transmitted yet. I/O returns to
59the same state as after calling
60:ref:`VIDIOC_REQBUFS` and can be restarted
61accordingly.
62
63If buffers have been queued with :ref:`VIDIOC_QBUF` and
64``VIDIOC_STREAMOFF`` is called without ever having called
65``VIDIOC_STREAMON``, then those queued buffers will also be removed from
66the incoming queue and all are returned to the same state as after
67calling :ref:`VIDIOC_REQBUFS` and can be restarted
68accordingly.
69
70Both ioctls take a pointer to an integer, the desired buffer or stream
71type. This is the same as struct
72:c:type:`v4l2_requestbuffers` ``type``.
73
74If ``VIDIOC_STREAMON`` is called when streaming is already in progress,
75or if ``VIDIOC_STREAMOFF`` is called when streaming is already stopped,
76then 0 is returned. Nothing happens in the case of ``VIDIOC_STREAMON``,
77but ``VIDIOC_STREAMOFF`` will return queued buffers to their starting
78state as mentioned above.
79
80.. note::
81
82   Applications can be preempted for unknown periods right before
83   or after the ``VIDIOC_STREAMON`` or ``VIDIOC_STREAMOFF`` calls, there is
84   no notion of starting or stopping "now". Buffer timestamps can be used
85   to synchronize with other events.
86
87Return Value
88============
89
90On success 0 is returned, on error -1 and the ``errno`` variable is set
91appropriately. The generic error codes are described at the
92:ref:`Generic Error Codes <gen-errors>` chapter.
93
94EINVAL
95    The buffer ``type`` is not supported, or no buffers have been
96    allocated (memory mapping) or enqueued (output) yet.
97
98EPIPE
99    The driver implements
100    :ref:`pad-level format configuration <pad-level-formats>` and the
101    pipeline configuration is invalid.
102
103ENOLINK
104    The driver implements Media Controller interface and the pipeline
105    link configuration is invalid.
106