| .. -*- 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, 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. |
| |
| .. 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. |
