0001 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
0002 .. c:namespace:: V4L
0003
0004 .. _VIDIOC_QUERYSTD:
0005
0006 *********************************************
0007 ioctl VIDIOC_QUERYSTD, VIDIOC_SUBDEV_QUERYSTD
0008 *********************************************
0009
0010 Name
0011 ====
0012
0013 VIDIOC_QUERYSTD - VIDIOC_SUBDEV_QUERYSTD - Sense the video standard received by the current input
0014
0015 Synopsis
0016 ========
0017
0018 .. c:macro:: VIDIOC_QUERYSTD
0019
0020 ``int ioctl(int fd, VIDIOC_QUERYSTD, v4l2_std_id *argp)``
0021
0022 .. c:macro:: VIDIOC_SUBDEV_QUERYSTD
0023
0024 ``int ioctl(int fd, VIDIOC_SUBDEV_QUERYSTD, v4l2_std_id *argp)``
0025
0026 Arguments
0027 =========
0028
0029 ``fd``
0030 File descriptor returned by :c:func:`open()`.
0031
0032 ``argp``
0033 Pointer to :c:type:`v4l2_std_id`.
0034
0035 Description
0036 ===========
0037
0038 The hardware may be able to detect the current video standard
0039 automatically. To do so, applications call :ref:`VIDIOC_QUERYSTD` with a
0040 pointer to a :ref:`v4l2_std_id <v4l2-std-id>` type. The driver
0041 stores here a set of candidates, this can be a single flag or a set of
0042 supported standards if for example the hardware can only distinguish
0043 between 50 and 60 Hz systems. If no signal was detected, then the driver
0044 will return V4L2_STD_UNKNOWN. When detection is not possible or fails,
0045 the set must contain all standards supported by the current video input
0046 or output.
0047
0048 .. note::
0049
0050 Drivers shall *not* switch the video standard
0051 automatically if a new video standard is detected. Instead, drivers
0052 should send the ``V4L2_EVENT_SOURCE_CHANGE`` event (if they support
0053 this) and expect that userspace will take action by calling
0054 :ref:`VIDIOC_QUERYSTD`. The reason is that a new video standard can mean
0055 different buffer sizes as well, and you cannot change buffer sizes on
0056 the fly. In general, applications that receive the Source Change event
0057 will have to call :ref:`VIDIOC_QUERYSTD`, and if the detected video
0058 standard is valid they will have to stop streaming, set the new
0059 standard, allocate new buffers and start streaming again.
0060
0061 Return Value
0062 ============
0063
0064 On success 0 is returned, on error -1 and the ``errno`` variable is set
0065 appropriately. The generic error codes are described at the
0066 :ref:`Generic Error Codes <gen-errors>` chapter.
0067
0068 ENODATA
0069 Standard video timings are not supported for this input or output.
