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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.