67 lines
2.0 KiB
ReStructuredText
67 lines
2.0 KiB
ReStructuredText
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.. -*- coding: utf-8; mode: rst -*-
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.. _VIDIOC_QUERYSTD:
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*********************
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ioctl VIDIOC_QUERYSTD
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*********************
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Name
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====
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VIDIOC_QUERYSTD - Sense the video standard received by the current input
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Synopsis
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========
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.. c:function:: int ioctl( int fd, VIDIOC_QUERYSTD, v4l2_std_id *argp )
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:name: VIDIOC_QUERYSTD
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Arguments
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=========
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``fd``
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File descriptor returned by :ref:`open() <func-open>`.
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``argp``
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Description
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===========
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The hardware may be able to detect the current video standard
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automatically. To do so, applications call :ref:`VIDIOC_QUERYSTD` with a
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pointer to a :ref:`v4l2_std_id <v4l2-std-id>` type. The driver
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stores here a set of candidates, this can be a single flag or a set of
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supported standards if for example the hardware can only distinguish
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between 50 and 60 Hz systems. If no signal was detected, then the driver
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will return V4L2_STD_UNKNOWN. When detection is not possible or fails,
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the set must contain all standards supported by the current video input
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or output.
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.. note::
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Drivers shall *not* switch the video standard
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automatically if a new video standard is detected. Instead, drivers
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should send the ``V4L2_EVENT_SOURCE_CHANGE`` event (if they support
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this) and expect that userspace will take action by calling
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:ref:`VIDIOC_QUERYSTD`. The reason is that a new video standard can mean
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different buffer sizes as well, and you cannot change buffer sizes on
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the fly. In general, applications that receive the Source Change event
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will have to call :ref:`VIDIOC_QUERYSTD`, and if the detected video
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standard is valid they will have to stop streaming, set the new
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standard, allocate new buffers and start streaming again.
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Return Value
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============
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On success 0 is returned, on error -1 and the ``errno`` variable is set
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appropriately. The generic error codes are described at the
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:ref:`Generic Error Codes <gen-errors>` chapter.
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ENODATA
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Standard video timings are not supported for this input or output.
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