70 lines
2.2 KiB
ReStructuredText
70 lines
2.2 KiB
ReStructuredText
|
.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
|
||
|
|
.. c:namespace:: V4L
|
||
|
|
|
||
|
|
.. _VIDIOC_QUERYSTD:
|
||
|
|
|
||
|
|
*********************************************
|
||
|
|
ioctl VIDIOC_QUERYSTD, VIDIOC_SUBDEV_QUERYSTD
|
||
|
|
*********************************************
|
||
|
|
|
||
|
|
Name
|
||
|
|
====
|
||
|
|
|
||
|
|
VIDIOC_QUERYSTD - VIDIOC_SUBDEV_QUERYSTD - Sense the video standard received by the current input
|
||
|
|
|
||
|
|
Synopsis
|
||
|
|
========
|
||
|
|
|
||
|
|
.. c:macro:: VIDIOC_QUERYSTD
|
||
|
|
|
||
|
|
``int ioctl(int fd, VIDIOC_QUERYSTD, v4l2_std_id *argp)``
|
||
|
|
|
||
|
|
.. c:macro:: VIDIOC_SUBDEV_QUERYSTD
|
||
|
|
|
||
|
|
``int ioctl(int fd, VIDIOC_SUBDEV_QUERYSTD, v4l2_std_id *argp)``
|
||
|
|
|
||
|
|
Arguments
|
||
|
|
=========
|
||
|
|
|
||
|
|
``fd``
|
||
|
|
File descriptor returned by :c:func:`open()`.
|
||
|
|
|
||
|
|
``argp``
|
||
|
|
Pointer to :c:type:`v4l2_std_id`.
|
||
|
|
|
||
|
|
Description
|
||
|
|
===========
|
||
|
|
|
||
|
|
The hardware may be able to detect the current video standard
|
||
|
|
automatically. To do so, applications call :ref:`VIDIOC_QUERYSTD` with a
|
||
|
|
pointer to a :ref:`v4l2_std_id <v4l2-std-id>` type. The driver
|
||
|
|
stores here a set of candidates, this can be a single flag or a set of
|
||
|
|
supported standards if for example the hardware can only distinguish
|
||
|
|
between 50 and 60 Hz systems. If no signal was detected, then the driver
|
||
|
|
will return V4L2_STD_UNKNOWN. When detection is not possible or fails,
|
||
|
|
the set must contain all standards supported by the current video input
|
||
|
|
or output.
|
||
|
|
|
||
|
|
.. note::
|
||
|
|
|
||
|
|
Drivers shall *not* switch the video standard
|
||
|
|
automatically if a new video standard is 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_QUERYSTD`. The reason is that a new video standard can 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_QUERYSTD`, and if the detected video
|
||
|
|
standard is valid they will have to stop streaming, set the new
|
||
|
|
standard, allocate new buffers and start streaming again.
|
||
|
|
|
||
|
|
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
|
||
|
|
:ref:`Generic Error Codes <gen-errors>` chapter.
|
||
|
|
|
||
|
|
ENODATA
|
||
|
|
Standard video timings are not supported for this input or output.
|