7.54. ioctl VIDIOC_STREAMON, VIDIOC_STREAMOFF¶
7.54.1. Name¶
VIDIOC_STREAMON - VIDIOC_STREAMOFF - Start or stop streaming I/O
7.54.2. Synopsis¶
-
int
ioctl
(int fd, VIDIOC_STREAMON, const int *argp)¶
-
int
ioctl
(int fd, VIDIOC_STREAMOFF, const int *argp)¶
7.54.4. Description¶
The VIDIOC_STREAMON
and VIDIOC_STREAMOFF
ioctl start and stop
the capture or output process during streaming
(memory mapping, user pointer or
DMABUF) I/O.
Capture hardware is disabled and no input buffers are filled (if there
are any empty buffers in the incoming queue) until VIDIOC_STREAMON
has been called. Output hardware is disabled and no video signal is
produced until VIDIOC_STREAMON
has been called. The ioctl will
succeed when at least one output buffer is in the incoming queue.
Memory-to-memory devices will not start until VIDIOC_STREAMON
has
been called for both the capture and output stream types.
If VIDIOC_STREAMON
fails then any already queued buffers will remain
queued.
The VIDIOC_STREAMOFF
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
ioctl VIDIOC_REQBUFS and can be restarted
accordingly.
If buffers have been queued with ioctl VIDIOC_QBUF, VIDIOC_DQBUF and
VIDIOC_STREAMOFF
is called without ever having called
VIDIOC_STREAMON
, then those queued buffers will also be removed from
the incoming queue and all are returned to the same state as after
calling ioctl VIDIOC_REQBUFS and can be restarted
accordingly.
Both ioctls take a pointer to an integer, the desired buffer or stream
type. This is the same as struct
v4l2_requestbuffers
type
.
If VIDIOC_STREAMON
is called when streaming is already in progress,
or if VIDIOC_STREAMOFF
is called when streaming is already stopped,
then 0 is returned. Nothing happens in the case of VIDIOC_STREAMON
,
but VIDIOC_STREAMOFF
will return queued buffers to their starting
state as mentioned above.
Note
Applications can be preempted for unknown periods right before
or after the VIDIOC_STREAMON
or VIDIOC_STREAMOFF
calls, there is
no notion of starting or stopping "now". Buffer timestamps can be used
to synchronize with other events.
7.54.5. Return Value¶
On success 0 is returned, on error -1 and the errno
variable is set
appropriately. The generic error codes are described at the
Generic Error Codes chapter.
- EINVAL
- The buffer
type
is not supported, or no buffers have been allocated (memory mapping) or enqueued (output) yet. - EPIPE
- The driver implements pad-level format configuration and the pipeline configuration is invalid.
- ENOLINK
- The driver implements Media Controller interface and the pipeline link configuration is invalid.