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- .. 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.
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