Documentation/userspace-api/media/v4l/vidioc-query-dv-timings.rst
.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later .. c:namespace:: V4L
.. _VIDIOC_QUERY_DV_TIMINGS:
ioctl VIDIOC_QUERY_DV_TIMINGS
VIDIOC_QUERY_DV_TIMINGS - VIDIOC_SUBDEV_QUERY_DV_TIMINGS - Sense the DV preset received by the current input
.. c:macro:: VIDIOC_QUERY_DV_TIMINGS
int ioctl(int fd, VIDIOC_QUERY_DV_TIMINGS, struct v4l2_dv_timings *argp)
.. c:macro:: VIDIOC_SUBDEV_QUERY_DV_TIMINGS
int ioctl(int fd, VIDIOC_SUBDEV_QUERY_DV_TIMINGS, struct v4l2_dv_timings *argp)
fd
File descriptor returned by :c:func:open().
argp
Pointer to struct :c:type:v4l2_dv_timings.
The hardware may be able to detect the current DV timings automatically,
similar to sensing the video standard. To do so, applications call
:ref:VIDIOC_QUERY_DV_TIMINGS with a pointer to a struct
:c:type:v4l2_dv_timings. Once the hardware detects
the timings, it will fill in the timings structure.
.. note::
Drivers shall not switch timings automatically if new
timings are detected. Instead, drivers should send the
V4L2_EVENT_SOURCE_CHANGE event (if they support this) and expect
that userspace will take action by calling :ref:VIDIOC_QUERY_DV_TIMINGS.
The reason is that new timings usually mean different buffer sizes as
well, and you cannot change buffer sizes on the fly. In general,
applications that receive the Source Change event will have to call
:ref:VIDIOC_QUERY_DV_TIMINGS, and if the detected timings are valid they
will have to stop streaming, set the new timings, allocate new buffers
and start streaming again.
If the timings could not be detected because there was no signal, then
ENOLINK is returned. If a signal was detected, but it was unstable and
the receiver could not lock to the signal, then ENOLCK is returned. If
the receiver could lock to the signal, but the format is unsupported
(e.g. because the pixelclock is out of range of the hardware
capabilities), then the driver fills in whatever timings it could find
and returns ERANGE. In that case the application can call
:ref:VIDIOC_DV_TIMINGS_CAP to compare the
found timings with the hardware's capabilities in order to give more
precise feedback to the user.
On success 0 is returned, on error -1 and the errno variable is set
appropriately. The generic error codes are described at the
:ref:Generic Error Codes <gen-errors> chapter.
ENODATA Digital video timings are not supported for this input or output.
ENOLINK No timings could be detected because no signal was found.
ENOLCK The signal was unstable and the hardware could not lock on to it.
ERANGE Timings were found, but they are out of range of the hardware capabilities.