1 .. SPDX-License-Identifier: GFDL-1.1-no-invari
2
3 .. _standard:
4
5 ***************
6 Video Standards
7 ***************
8
9 Video devices typically support one or more di
10 variations of standards. Each video input and
11 set of standards. This set is reported by the
12 :c:type:`v4l2_input` and struct
13 :c:type:`v4l2_output` returned by the
14 :ref:`VIDIOC_ENUMINPUT` and
15 :ref:`VIDIOC_ENUMOUTPUT` ioctls, respectively.
16
17 V4L2 defines one bit for each analog video sta
18 worldwide, and sets aside bits for driver defi
19 hybrid standards to watch NTSC video tapes on
20 Applications can use the predefined bits to se
21 standard, although presenting the user a menu
22 preferred. To enumerate and query the attribut
23 standards applications use the :ref:`VIDIOC_EN
24 ioctl.
25
26 Many of the defined standards are actually jus
27 major standards. The hardware may in fact not
28 or do so internal and switch automatically. Th
29 standards also contain sets of one or more sta
30
31 Assume a hypothetic tuner capable of demodulat
32 signals. The first enumerated standard is a se
33 automatically depending on the selected radio
34 band. Enumeration gives a "PAL-B/G" or "PAL-I"
35 Composite input may collapse standards, enumer
36 "NTSC-M" and "SECAM-D/K". [#f1]_
37
38 To query and select the standard used by the c
39 output applications call the :ref:`VIDIOC_G_ST
40 :ref:`VIDIOC_S_STD <VIDIOC_G_STD>` ioctl, resp
41 *received* standard can be sensed with the
42 :ref:`VIDIOC_QUERYSTD` ioctl.
43
44 .. note::
45
46 The parameter of all these ioctls is a poin
47 :ref:`v4l2_std_id <v4l2-std-id>` type (a st
48 index into the standard enumeration. Driver
49 standard ioctls when the device has one or
50
51 Special rules apply to devices such as USB cam
52 video standards makes little sense. More gener
53 output device which is:
54
55 - incapable of capturing fields or frames at
56 video standard, or
57
58 - that does not support the video standard fo
59
60 Here the driver shall set the ``std`` field of
61 :c:type:`v4l2_input` and struct
62 :c:type:`v4l2_output` to zero and the :ref:`VI
63 :ref:`VIDIOC_S_STD <VIDIOC_G_STD>`, :ref:`VIDI
64 shall return the ``ENOTTY`` error code or the
65
66 Applications can make use of the :ref:`input-c
67 :ref:`output-capabilities` flags to determine
68 standard ioctls can be used with the given inp
69
70 Example: Information about the current video s
71 ==============================================
72
73 .. code-block:: c
74
75 v4l2_std_id std_id;
76 struct v4l2_standard standard;
77
78 if (-1 == ioctl(fd, VIDIOC_G_STD, &std_id)
79 /* Note when VIDIOC_ENUMSTD always ret
80 is no video device or it falls unde
81 and VIDIOC_G_STD returning ENOTTY i
82
83 perror("VIDIOC_G_STD");
84 exit(EXIT_FAILURE);
85 }
86
87 memset(&standard, 0, sizeof(standard));
88 standard.index = 0;
89
90 while (0 == ioctl(fd, VIDIOC_ENUMSTD, &sta
91 if (standard.id & std_id) {
92 printf("Current video standard:
93 exit(EXIT_SUCCESS);
94 }
95
96 standard.index++;
97 }
98
99 /* EINVAL indicates the end of the enumera
100 empty unless this device falls under th
101
102 if (errno == EINVAL || standard.index == 0
103 perror("VIDIOC_ENUMSTD");
104 exit(EXIT_FAILURE);
105 }
106
107 Example: Listing the video standards supported
108 ==============================================
109
110 .. code-block:: c
111
112 struct v4l2_input input;
113 struct v4l2_standard standard;
114
115 memset(&input, 0, sizeof(input));
116
117 if (-1 == ioctl(fd, VIDIOC_G_INPUT, &input
118 perror("VIDIOC_G_INPUT");
119 exit(EXIT_FAILURE);
120 }
121
122 if (-1 == ioctl(fd, VIDIOC_ENUMINPUT, &inp
123 perror("VIDIOC_ENUM_INPUT");
124 exit(EXIT_FAILURE);
125 }
126
127 printf("Current input %s supports:\\n", in
128
129 memset(&standard, 0, sizeof(standard));
130 standard.index = 0;
131
132 while (0 == ioctl(fd, VIDIOC_ENUMSTD, &sta
133 if (standard.id & input.std)
134 printf("%s\\n", standard.name);
135
136 standard.index++;
137 }
138
139 /* EINVAL indicates the end of the enumera
140 empty unless this device falls under th
141
142 if (errno != EINVAL || standard.index == 0
143 perror("VIDIOC_ENUMSTD");
144 exit(EXIT_FAILURE);
145 }
146
147 Example: Selecting a new video standard
148 =======================================
149
150 .. code-block:: c
151
152 struct v4l2_input input;
153 v4l2_std_id std_id;
154
155 memset(&input, 0, sizeof(input));
156
157 if (-1 == ioctl(fd, VIDIOC_G_INPUT, &input
158 perror("VIDIOC_G_INPUT");
159 exit(EXIT_FAILURE);
160 }
161
162 if (-1 == ioctl(fd, VIDIOC_ENUMINPUT, &inp
163 perror("VIDIOC_ENUM_INPUT");
164 exit(EXIT_FAILURE);
165 }
166
167 if (0 == (input.std & V4L2_STD_PAL_BG)) {
168 fprintf(stderr, "Oops. B/G PAL is not
169 exit(EXIT_FAILURE);
170 }
171
172 /* Note this is also supposed to work when
173 or G/PAL is supported. */
174
175 std_id = V4L2_STD_PAL_BG;
176
177 if (-1 == ioctl(fd, VIDIOC_S_STD, &std_id)
178 perror("VIDIOC_S_STD");
179 exit(EXIT_FAILURE);
180 }
181
182 .. [#f1]
183 Some users are already confused by technica
184 SECAM. There is no point asking them to dis
185 or K when the software or hardware can do t
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