vidioc-querystd.rst (2258B)
1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later 2.. c:namespace:: V4L 3 4.. _VIDIOC_QUERYSTD: 5 6********************************************* 7ioctl VIDIOC_QUERYSTD, VIDIOC_SUBDEV_QUERYSTD 8********************************************* 9 10Name 11==== 12 13VIDIOC_QUERYSTD - VIDIOC_SUBDEV_QUERYSTD - Sense the video standard received by the current input 14 15Synopsis 16======== 17 18.. c:macro:: VIDIOC_QUERYSTD 19 20``int ioctl(int fd, VIDIOC_QUERYSTD, v4l2_std_id *argp)`` 21 22.. c:macro:: VIDIOC_SUBDEV_QUERYSTD 23 24``int ioctl(int fd, VIDIOC_SUBDEV_QUERYSTD, v4l2_std_id *argp)`` 25 26Arguments 27========= 28 29``fd`` 30 File descriptor returned by :c:func:`open()`. 31 32``argp`` 33 Pointer to :c:type:`v4l2_std_id`. 34 35Description 36=========== 37 38The hardware may be able to detect the current video standard 39automatically. To do so, applications call :ref:`VIDIOC_QUERYSTD` with a 40pointer to a :ref:`v4l2_std_id <v4l2-std-id>` type. The driver 41stores here a set of candidates, this can be a single flag or a set of 42supported standards if for example the hardware can only distinguish 43between 50 and 60 Hz systems. If no signal was detected, then the driver 44will return V4L2_STD_UNKNOWN. When detection is not possible or fails, 45the set must contain all standards supported by the current video input 46or output. 47 48.. note:: 49 50 Drivers shall *not* switch the video standard 51 automatically if a new video standard is detected. Instead, drivers 52 should send the ``V4L2_EVENT_SOURCE_CHANGE`` event (if they support 53 this) and expect that userspace will take action by calling 54 :ref:`VIDIOC_QUERYSTD`. The reason is that a new video standard can mean 55 different buffer sizes as well, and you cannot change buffer sizes on 56 the fly. In general, applications that receive the Source Change event 57 will have to call :ref:`VIDIOC_QUERYSTD`, and if the detected video 58 standard is valid they will have to stop streaming, set the new 59 standard, allocate new buffers and start streaming again. 60 61Return Value 62============ 63 64On success 0 is returned, on error -1 and the ``errno`` variable is set 65appropriately. The generic error codes are described at the 66:ref:`Generic Error Codes <gen-errors>` chapter. 67 68ENODATA 69 Standard video timings are not supported for this input or output.