projects / deliverable / linux.git / blame
| Commit | Line | Data |
|---|---|---|
| 5377d91f MH |
1 | .. -*- coding: utf-8; mode: rst -*- |
| 2 | ||
| af4a4d0d | 3 | .. _VIDIOC_QUERYSTD: |
| 5377d91f MH |
4 | |
| 5 | ********************* | |
| 6 | ioctl VIDIOC_QUERYSTD | |
| 7 | ********************* | |
| 8 | ||
| 15e7d615 | 9 | Name |
| 586027ce | 10 | ==== |
| 5377d91f | 11 | |
| 586027ce | 12 | VIDIOC_QUERYSTD - Sense the video standard received by the current input |
| 5377d91f | 13 | |
| 15e7d615 MCC |
14 | |
| 15 | Synopsis | |
| 5377d91f MH |
16 | ======== |
| 17 | ||
| 41d80465 MCC |
18 | .. c:function:: int ioctl( int fd, VIDIOC_QUERYSTD, v4l2_std_id *argp ) |
| 19 | :name: VIDIOC_QUERYSTD | |
| 5377d91f | 20 | |
| 586027ce | 21 | |
| 15e7d615 | 22 | Arguments |
| 5377d91f MH |
23 | ========= |
| 24 | ||
| 25 | ``fd`` | |
| 26 | File descriptor returned by :ref:`open() <func-open>`. | |
| 27 | ||
| 5377d91f MH |
28 | ``argp`` |
| 29 | ||
| 30 | ||
| 15e7d615 | 31 | Description |
| 5377d91f MH |
32 | =========== |
| 33 | ||
| 34 | The hardware may be able to detect the current video standard | |
| 2212ff25 | 35 | automatically. To do so, applications call :ref:`VIDIOC_QUERYSTD` with a |
| 5377d91f MH |
36 | pointer to a :ref:`v4l2_std_id <v4l2-std-id>` type. The driver |
| 37 | stores here a set of candidates, this can be a single flag or a set of | |
| 38 | supported standards if for example the hardware can only distinguish | |
| 39 | between 50 and 60 Hz systems. If no signal was detected, then the driver | |
| 40 | will return V4L2_STD_UNKNOWN. When detection is not possible or fails, | |
| 41 | the set must contain all standards supported by the current video input | |
| 42 | or output. | |
| 43 | ||
| b6b6e678 MCC |
44 | .. note:: |
| 45 | ||
| 46 | Drivers shall *not* switch the video standard | |
| 706f8a99 MCC |
47 | automatically if a new video standard is detected. Instead, drivers |
| 48 | should send the ``V4L2_EVENT_SOURCE_CHANGE`` event (if they support | |
| 49 | this) and expect that userspace will take action by calling | |
| 50 | :ref:`VIDIOC_QUERYSTD`. The reason is that a new video standard can mean | |
| 51 | different buffer sizes as well, and you cannot change buffer sizes on | |
| 52 | the fly. In general, applications that receive the Source Change event | |
| 53 | will have to call :ref:`VIDIOC_QUERYSTD`, and if the detected video | |
| 54 | standard is valid they will have to stop streaming, set the new | |
| 55 | standard, allocate new buffers and start streaming again. | |
| 5377d91f MH |
56 | |
| 57 | ||
| 15e7d615 | 58 | Return Value |
| 5377d91f MH |
59 | ============ |
| 60 | ||
| 61 | On success 0 is returned, on error -1 and the ``errno`` variable is set | |
| 62 | appropriately. The generic error codes are described at the | |
| 63 | :ref:`Generic Error Codes <gen-errors>` chapter. | |
| 64 | ||
| 65 | ENODATA | |
| 66 | Standard video timings are not supported for this input or output. |