1 .. SPDX-License-Identifier: GFDL-1.1-no-invari
2 .. c:namespace:: V4L
3
4 .. _VIDIOC_G_PARM:
5
6 **********************************
7 ioctl VIDIOC_G_PARM, VIDIOC_S_PARM
8 **********************************
9
10 Name
11 ====
12
13 VIDIOC_G_PARM - VIDIOC_S_PARM - Get or set str
14
15 Synopsis
16 ========
17
18 .. c:macro:: VIDIOC_G_PARM
19
20 ``int ioctl(int fd, VIDIOC_G_PARM, v4l2_stream
21
22 .. c:macro:: VIDIOC_S_PARM
23
24 ``int ioctl(int fd, VIDIOC_S_PARM, v4l2_stream
25
26 Arguments
27 =========
28
29 ``fd``
30 File descriptor returned by :c:func:`open(
31
32 ``argp``
33 Pointer to struct :c:type:`v4l2_streamparm
34
35 Description
36 ===========
37
38 Applications can request a different frame int
39 output device will be reconfigured to support
40 interval if possible. Optionally drivers may c
41 repeat frames to achieve the requested frame i
42
43 For stateful encoders (see :ref:`encoder`) thi
44 frame interval that is typically embedded in t
45
46 Changing the frame interval shall never change
47 format, on the other hand, may change the fram
48
49 Further these ioctls can be used to determine
50 internally by a driver in read/write mode. For
51 section discussing the :c:func:`read()` functi
52
53 To get and set the streaming parameters applic
54 :ref:`VIDIOC_G_PARM <VIDIOC_G_PARM>` and
55 :ref:`VIDIOC_S_PARM <VIDIOC_G_PARM>` ioctl, re
56 pointer to a struct :c:type:`v4l2_streamparm`
57 union holding separate parameters for input an
58
59 .. tabularcolumns:: |p{3.7cm}|p{3.5cm}|p{10.1c
60
61 .. c:type:: v4l2_streamparm
62
63 .. flat-table:: struct v4l2_streamparm
64 :header-rows: 0
65 :stub-columns: 0
66 :widths: 1 1 2
67
68 * - __u32
69 - ``type``
70 - The buffer (stream) type, same as stru
71 :c:type:`v4l2_format` ``type``, set by
72 application. See :c:type:`v4l2_buf_typ
73 * - union {
74 - ``parm``
75 * - struct :c:type:`v4l2_captureparm`
76 - ``capture``
77 - Parameters for capture devices, used w
78 ``V4L2_BUF_TYPE_VIDEO_CAPTURE`` or
79 ``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE``
80 * - struct :c:type:`v4l2_outputparm`
81 - ``output``
82 - Parameters for output devices, used wh
83 ``V4L2_BUF_TYPE_VIDEO_OUTPUT`` or ``V4
84 * - __u8
85 - ``raw_data``\ [200]
86 - A place holder for future extensions.
87 * - }
88
89
90 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm
91
92 .. c:type:: v4l2_captureparm
93
94 .. flat-table:: struct v4l2_captureparm
95 :header-rows: 0
96 :stub-columns: 0
97 :widths: 1 1 2
98
99 * - __u32
100 - ``capability``
101 - See :ref:`parm-caps`.
102 * - __u32
103 - ``capturemode``
104 - Set by drivers and applications, see :
105 * - struct :c:type:`v4l2_fract`
106 - ``timeperframe``
107 - This is the desired period between suc
108 the driver, in seconds.
109 * - :cspan:`2`
110
111 This will configure the speed at which
112 generates video frames. If the speed i
113 choose to skip or repeat frames in ord
114 frame rate.
115
116 For stateful encoders (see :ref:`encod
117 frame interval that is typically embed
118
119 Applications store here the desired fr
120 the actual frame period.
121
122 Changing the video standard (also impl
123 the video input) may reset this parame
124 period. To reset manually applications
125 zero.
126
127 Drivers support this function only whe
128 ``V4L2_CAP_TIMEPERFRAME`` flag in the
129 * - __u32
130 - ``extendedmode``
131 - Custom (driver specific) streaming par
132 applications and drivers must set this
133 using this field should check the driv
134 :ref:`querycap`.
135 * - __u32
136 - ``readbuffers``
137 - Applications set this field to the des
138 internally by the driver in :c:func:`r
139 Drivers return the actual number of bu
140 requests zero buffers, drivers should
141 setting rather than the minimum or an
142 :ref:`rw`.
143 * - __u32
144 - ``reserved``\ [4]
145 - Reserved for future extensions. Driver
146 the array to zero.
147
148
149 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm
150
151 .. c:type:: v4l2_outputparm
152
153 .. flat-table:: struct v4l2_outputparm
154 :header-rows: 0
155 :stub-columns: 0
156 :widths: 1 1 2
157
158 * - __u32
159 - ``capability``
160 - See :ref:`parm-caps`.
161 * - __u32
162 - ``outputmode``
163 - Set by drivers and applications, see :
164 * - struct :c:type:`v4l2_fract`
165 - ``timeperframe``
166 - This is the desired period between suc
167 driver, in seconds.
168 * - :cspan:`2`
169
170 The field is intended to repeat frames
171 :c:func:`write()` mode (in streaming m
172 can be used to throttle the output), s
173
174 For stateful encoders (see :ref:`encod
175 frame interval that is typically embed
176 and it provides a hint to the encoder
177 frames are queued up to the encoder.
178
179 Applications store here the desired fr
180 the actual frame period.
181
182 Changing the video standard (also impl
183 the video output) may reset this param
184 period. To reset manually applications
185 zero.
186
187 Drivers support this function only whe
188 ``V4L2_CAP_TIMEPERFRAME`` flag in the
189 * - __u32
190 - ``extendedmode``
191 - Custom (driver specific) streaming par
192 applications and drivers must set this
193 using this field should check the driv
194 :ref:`querycap`.
195 * - __u32
196 - ``writebuffers``
197 - Applications set this field to the des
198 internally by the driver in :c:func:`w
199 return the actual number of buffers. W
200 zero buffers, drivers should just retu
201 rather than the minimum or an error co
202 :ref:`rw`.
203 * - __u32
204 - ``reserved``\ [4]
205 - Reserved for future extensions. Driver
206 the array to zero.
207
208
209 .. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.5cm
210
211 .. _parm-caps:
212
213 .. flat-table:: Streaming Parameters Capabilit
214 :header-rows: 0
215 :stub-columns: 0
216 :widths: 3 1 4
217
218 * - ``V4L2_CAP_TIMEPERFRAME``
219 - 0x1000
220 - The frame period can be modified by se
221 field.
222
223
224 .. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.5cm
225
226 .. _parm-flags:
227
228 .. flat-table:: Capture Parameters Flags
229 :header-rows: 0
230 :stub-columns: 0
231 :widths: 3 1 4
232
233 * - ``V4L2_MODE_HIGHQUALITY``
234 - 0x0001
235 - High quality imaging mode. High qualit
236 imaging applications. The idea is to g
237 quality that the hardware can deliver.
238 driver writer may achieve that; it wil
239 the ingenuity of the driver writer. Hi
240 different mode from the regular motion
241 high quality mode:
242
243 - The driver may be able to capture h
244 motion capture.
245
246 - The driver may support fewer pixel
247 (eg; true color).
248
249 - The driver may capture and arithmet
250 successive fields or frames to remo
251 reduce the noise in the video data.
252
253 - The driver may capture images in sl
254 to handle larger format images than
255 possible.
256
257 - An image capture operation may be s
258 motion capture.
259
260 - Moving objects in the image might h
261
262 - Capture might only work through the
263
264 Return Value
265 ============
266
267 On success 0 is returned, on error -1 and the
268 appropriately. The generic error codes are des
269 :ref:`Generic Error Codes <gen-errors>` chapte
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