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diff --git a/Documentation/media/uapi/v4l/vidioc-querystd.rst b/Documentation/media/uapi/v4l/vidioc-querystd.rst new file mode 100644 index 0000000..5bf6277 --- /dev/null +++ b/Documentation/media/uapi/v4l/vidioc-querystd.rst @@ -0,0 +1,66 @@ +.. -*- coding: utf-8; mode: rst -*- + +.. _VIDIOC_QUERYSTD: + +********************* +ioctl VIDIOC_QUERYSTD +********************* + +Name +==== + +VIDIOC_QUERYSTD - Sense the video standard received by the current input + + +Synopsis +======== + +.. cpp:function:: int ioctl( int fd, int request, v4l2_std_id *argp ) + + +Arguments +========= + +``fd`` + File descriptor returned by :ref:`open() <func-open>`. + +``request`` + VIDIOC_QUERYSTD + +``argp`` + + +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. + +Please note that 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. |