1 .. SPDX-License-Identifier: GFDL-1.1-no-invari 1 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
2 .. c:namespace:: V4L 2 .. c:namespace:: V4L
3 3
4 .. _VIDIOC_QUERYSTD: 4 .. _VIDIOC_QUERYSTD:
5 5
6 ********************************************* 6 *********************************************
7 ioctl VIDIOC_QUERYSTD, VIDIOC_SUBDEV_QUERYSTD 7 ioctl VIDIOC_QUERYSTD, VIDIOC_SUBDEV_QUERYSTD
8 ********************************************* 8 *********************************************
9 9
10 Name 10 Name
11 ==== 11 ====
12 12
13 VIDIOC_QUERYSTD - VIDIOC_SUBDEV_QUERYSTD - Sen 13 VIDIOC_QUERYSTD - VIDIOC_SUBDEV_QUERYSTD - Sense the video standard received by the current input
14 14
15 Synopsis 15 Synopsis
16 ======== 16 ========
17 17
18 .. c:macro:: VIDIOC_QUERYSTD 18 .. c:macro:: VIDIOC_QUERYSTD
19 19
20 ``int ioctl(int fd, VIDIOC_QUERYSTD, v4l2_std_ 20 ``int ioctl(int fd, VIDIOC_QUERYSTD, v4l2_std_id *argp)``
21 21
22 .. c:macro:: VIDIOC_SUBDEV_QUERYSTD 22 .. c:macro:: VIDIOC_SUBDEV_QUERYSTD
23 23
24 ``int ioctl(int fd, VIDIOC_SUBDEV_QUERYSTD, v4 24 ``int ioctl(int fd, VIDIOC_SUBDEV_QUERYSTD, v4l2_std_id *argp)``
25 25
26 Arguments 26 Arguments
27 ========= 27 =========
28 28
29 ``fd`` 29 ``fd``
30 File descriptor returned by :c:func:`open( 30 File descriptor returned by :c:func:`open()`.
31 31
32 ``argp`` 32 ``argp``
33 Pointer to :c:type:`v4l2_std_id`. 33 Pointer to :c:type:`v4l2_std_id`.
34 34
35 Description 35 Description
36 =========== 36 ===========
37 37
38 The hardware may be able to detect the current 38 The hardware may be able to detect the current video standard
39 automatically. To do so, applications call :re 39 automatically. To do so, applications call :ref:`VIDIOC_QUERYSTD` with a
40 pointer to a :ref:`v4l2_std_id <v4l2-std-id>` 40 pointer to a :ref:`v4l2_std_id <v4l2-std-id>` type. The driver
41 stores here a set of candidates, this can be a 41 stores here a set of candidates, this can be a single flag or a set of
42 supported standards if for example the hardwar 42 supported standards if for example the hardware can only distinguish
43 between 50 and 60 Hz systems. If no signal was 43 between 50 and 60 Hz systems. If no signal was detected, then the driver
44 will return V4L2_STD_UNKNOWN. When detection i 44 will return V4L2_STD_UNKNOWN. When detection is not possible or fails,
45 the set must contain all standards supported b 45 the set must contain all standards supported by the current video input
46 or output. 46 or output.
47 47
48 .. note:: 48 .. note::
49 49
50 Drivers shall *not* switch the video standa 50 Drivers shall *not* switch the video standard
51 automatically if a new video standard is de 51 automatically if a new video standard is detected. Instead, drivers
52 should send the ``V4L2_EVENT_SOURCE_CHANGE` 52 should send the ``V4L2_EVENT_SOURCE_CHANGE`` event (if they support
53 this) and expect that userspace will take a 53 this) and expect that userspace will take action by calling
54 :ref:`VIDIOC_QUERYSTD`. The reason is that 54 :ref:`VIDIOC_QUERYSTD`. The reason is that a new video standard can mean
55 different buffer sizes as well, and you can 55 different buffer sizes as well, and you cannot change buffer sizes on
56 the fly. In general, applications that rece 56 the fly. In general, applications that receive the Source Change event
57 will have to call :ref:`VIDIOC_QUERYSTD`, a 57 will have to call :ref:`VIDIOC_QUERYSTD`, and if the detected video
58 standard is valid they will have to stop st 58 standard is valid they will have to stop streaming, set the new
59 standard, allocate new buffers and start st 59 standard, allocate new buffers and start streaming again.
60 60
61 Return Value 61 Return Value
62 ============ 62 ============
63 63
64 On success 0 is returned, on error -1 and the 64 On success 0 is returned, on error -1 and the ``errno`` variable is set
65 appropriately. The generic error codes are des 65 appropriately. The generic error codes are described at the
66 :ref:`Generic Error Codes <gen-errors>` chapte 66 :ref:`Generic Error Codes <gen-errors>` chapter.
67 67
68 ENODATA 68 ENODATA
69 Standard video timings are not supported f 69 Standard video timings are not supported for this input or output.
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.