162306a36Sopenharmony_ci.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later 262306a36Sopenharmony_ci.. c:namespace:: V4L 362306a36Sopenharmony_ci 462306a36Sopenharmony_ci.. _VIDIOC_QUERYSTD: 562306a36Sopenharmony_ci 662306a36Sopenharmony_ci********************************************* 762306a36Sopenharmony_ciioctl VIDIOC_QUERYSTD, VIDIOC_SUBDEV_QUERYSTD 862306a36Sopenharmony_ci********************************************* 962306a36Sopenharmony_ci 1062306a36Sopenharmony_ciName 1162306a36Sopenharmony_ci==== 1262306a36Sopenharmony_ci 1362306a36Sopenharmony_ciVIDIOC_QUERYSTD - VIDIOC_SUBDEV_QUERYSTD - Sense the video standard received by the current input 1462306a36Sopenharmony_ci 1562306a36Sopenharmony_ciSynopsis 1662306a36Sopenharmony_ci======== 1762306a36Sopenharmony_ci 1862306a36Sopenharmony_ci.. c:macro:: VIDIOC_QUERYSTD 1962306a36Sopenharmony_ci 2062306a36Sopenharmony_ci``int ioctl(int fd, VIDIOC_QUERYSTD, v4l2_std_id *argp)`` 2162306a36Sopenharmony_ci 2262306a36Sopenharmony_ci.. c:macro:: VIDIOC_SUBDEV_QUERYSTD 2362306a36Sopenharmony_ci 2462306a36Sopenharmony_ci``int ioctl(int fd, VIDIOC_SUBDEV_QUERYSTD, v4l2_std_id *argp)`` 2562306a36Sopenharmony_ci 2662306a36Sopenharmony_ciArguments 2762306a36Sopenharmony_ci========= 2862306a36Sopenharmony_ci 2962306a36Sopenharmony_ci``fd`` 3062306a36Sopenharmony_ci File descriptor returned by :c:func:`open()`. 3162306a36Sopenharmony_ci 3262306a36Sopenharmony_ci``argp`` 3362306a36Sopenharmony_ci Pointer to :c:type:`v4l2_std_id`. 3462306a36Sopenharmony_ci 3562306a36Sopenharmony_ciDescription 3662306a36Sopenharmony_ci=========== 3762306a36Sopenharmony_ci 3862306a36Sopenharmony_ciThe hardware may be able to detect the current video standard 3962306a36Sopenharmony_ciautomatically. To do so, applications call :ref:`VIDIOC_QUERYSTD` with a 4062306a36Sopenharmony_cipointer to a :ref:`v4l2_std_id <v4l2-std-id>` type. The driver 4162306a36Sopenharmony_cistores here a set of candidates, this can be a single flag or a set of 4262306a36Sopenharmony_cisupported standards if for example the hardware can only distinguish 4362306a36Sopenharmony_cibetween 50 and 60 Hz systems. If no signal was detected, then the driver 4462306a36Sopenharmony_ciwill return V4L2_STD_UNKNOWN. When detection is not possible or fails, 4562306a36Sopenharmony_cithe set must contain all standards supported by the current video input 4662306a36Sopenharmony_cior output. 4762306a36Sopenharmony_ci 4862306a36Sopenharmony_ci.. note:: 4962306a36Sopenharmony_ci 5062306a36Sopenharmony_ci Drivers shall *not* switch the video standard 5162306a36Sopenharmony_ci automatically if a new video standard is detected. Instead, drivers 5262306a36Sopenharmony_ci should send the ``V4L2_EVENT_SOURCE_CHANGE`` event (if they support 5362306a36Sopenharmony_ci this) and expect that userspace will take action by calling 5462306a36Sopenharmony_ci :ref:`VIDIOC_QUERYSTD`. The reason is that a new video standard can mean 5562306a36Sopenharmony_ci different buffer sizes as well, and you cannot change buffer sizes on 5662306a36Sopenharmony_ci the fly. In general, applications that receive the Source Change event 5762306a36Sopenharmony_ci will have to call :ref:`VIDIOC_QUERYSTD`, and if the detected video 5862306a36Sopenharmony_ci standard is valid they will have to stop streaming, set the new 5962306a36Sopenharmony_ci standard, allocate new buffers and start streaming again. 6062306a36Sopenharmony_ci 6162306a36Sopenharmony_ciReturn Value 6262306a36Sopenharmony_ci============ 6362306a36Sopenharmony_ci 6462306a36Sopenharmony_ciOn success 0 is returned, on error -1 and the ``errno`` variable is set 6562306a36Sopenharmony_ciappropriately. The generic error codes are described at the 6662306a36Sopenharmony_ci:ref:`Generic Error Codes <gen-errors>` chapter. 6762306a36Sopenharmony_ci 6862306a36Sopenharmony_ciENODATA 6962306a36Sopenharmony_ci Standard video timings are not supported for this input or output. 70