| .. -*- coding: utf-8; mode: rst -*- | |
| .. _VIDIOC_QUERYSTD: | |
| ********************* | |
| ioctl VIDIOC_QUERYSTD | |
| ********************* | |
| Name | |
| ==== | |
| VIDIOC_QUERYSTD - Sense the video standard received by the current input | |
| Synopsis | |
| ======== | |
| .. c:function:: int ioctl( int fd, VIDIOC_QUERYSTD, v4l2_std_id *argp ) | |
| :name: VIDIOC_QUERYSTD | |
| Arguments | |
| ========= | |
| ``fd`` | |
| File descriptor returned by :ref:`open() <func-open>`. | |
| ``argp`` | |
| Pointer to :c:type:`v4l2_std_id`. | |
| 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. | |
| .. note:: | |
| 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. |