1 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later 2 .. c:namespace:: V4L 3 4 .. _VIDIOC_STREAMON: 5 6 *************************************** 7 ioctl VIDIOC_STREAMON, VIDIOC_STREAMOFF 8 *************************************** 9 10 Name 11 ==== 12 13 VIDIOC_STREAMON - VIDIOC_STREAMOFF - Start or stop streaming I/O 14 15 Synopsis 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 26 Arguments 27 ========= 28 29 ``fd`` 30 File descriptor returned by :c:func:`open()`. 31 32 ``argp`` 33 Pointer to an integer. 34 35 Description 36 =========== 37 38 The ``VIDIOC_STREAMON`` and ``VIDIOC_STREAMOFF`` ioctl start and stop 39 the capture or output process during streaming 40 (:ref:`memory mapping <mmap>`, :ref:`user pointer <userp>` or 41 :ref:`DMABUF <dmabuf>`) I/O. 42 43 Capture hardware is disabled and no input buffers are filled (if there 44 are any empty buffers in the incoming queue) until ``VIDIOC_STREAMON`` 45 has been called. Output hardware is disabled and no video signal is 46 produced until ``VIDIOC_STREAMON`` has been called. 47 48 Memory-to-memory devices will not start until ``VIDIOC_STREAMON`` has 49 been called for both the capture and output stream types. 50 51 If ``VIDIOC_STREAMON`` fails then any already queued buffers will remain 52 queued. 53 54 The ``VIDIOC_STREAMOFF`` ioctl, apart of aborting or finishing any DMA 55 in progress, unlocks any user pointer buffers locked in physical memory, 56 and it removes all buffers from the incoming and outgoing queues. That 57 means all images captured but not dequeued yet will be lost, likewise 58 all images enqueued for output but not transmitted yet. I/O returns to 59 the same state as after calling 60 :ref:`VIDIOC_REQBUFS` and can be restarted 61 accordingly. 62 63 If 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 66 the incoming queue and all are returned to the same state as after 67 calling :ref:`VIDIOC_REQBUFS` and can be restarted 68 accordingly. 69 70 Both ioctls take a pointer to an integer, the desired buffer or stream 71 type. This is the same as struct 72 :c:type:`v4l2_requestbuffers` ``type``. 73 74 If ``VIDIOC_STREAMON`` is called when streaming is already in progress, 75 or if ``VIDIOC_STREAMOFF`` is called when streaming is already stopped, 76 then 0 is returned. Nothing happens in the case of ``VIDIOC_STREAMON``, 77 but ``VIDIOC_STREAMOFF`` will return queued buffers to their starting 78 state 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 87 Return Value 88 ============ 89 90 On success 0 is returned, on error -1 and the ``errno`` variable is set 91 appropriately. The generic error codes are described at the 92 :ref:`Generic Error Codes <gen-errors>` chapter. 93 94 EINVAL 95 The buffer ``type`` is not supported, or no buffers have been 96 allocated (memory mapping) or enqueued (output) yet. 97 98 EPIPE 99 The driver implements 100 :ref:`pad-level format configuration <pad-level-formats>` and the 101 pipeline configuration is invalid. 102 103 ENOLINK 104 The driver implements Media Controller interface and the pipeline 105 link configuration is invalid.
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