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1 | .. -*- coding: utf-8; mode: rst -*- |
2 | ||
af4a4d0d | 3 | .. _VIDIOC_QUERYSTD: |
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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 | |
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14 | |
15 | Synopsis | |
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16 | ======== |
17 | ||
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18 | .. c:function:: int ioctl( int fd, VIDIOC_QUERYSTD, v4l2_std_id *argp ) |
19 | :name: VIDIOC_QUERYSTD | |
5377d91f | 20 | |
586027ce | 21 | |
15e7d615 | 22 | Arguments |
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23 | ========= |
24 | ||
25 | ``fd`` | |
26 | File descriptor returned by :ref:`open() <func-open>`. | |
27 | ||
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28 | ``argp`` |
29 | ||
30 | ||
15e7d615 | 31 | Description |
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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 |
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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 | ||
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44 | .. note:: |
45 | ||
46 | Drivers shall *not* switch the video standard | |
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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. | |
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56 | |
57 | ||
15e7d615 | 58 | Return Value |
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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. |