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_G_PARM: 4 .. _VIDIOC_G_PARM:
5 5
6 ********************************** 6 **********************************
7 ioctl VIDIOC_G_PARM, VIDIOC_S_PARM 7 ioctl VIDIOC_G_PARM, VIDIOC_S_PARM
8 ********************************** 8 **********************************
9 9
10 Name 10 Name
11 ==== 11 ====
12 12
13 VIDIOC_G_PARM - VIDIOC_S_PARM - Get or set str 13 VIDIOC_G_PARM - VIDIOC_S_PARM - Get or set streaming parameters
14 14
15 Synopsis 15 Synopsis
16 ======== 16 ========
17 17
18 .. c:macro:: VIDIOC_G_PARM 18 .. c:macro:: VIDIOC_G_PARM
19 19
20 ``int ioctl(int fd, VIDIOC_G_PARM, v4l2_stream 20 ``int ioctl(int fd, VIDIOC_G_PARM, v4l2_streamparm *argp)``
21 21
22 .. c:macro:: VIDIOC_S_PARM 22 .. c:macro:: VIDIOC_S_PARM
23 23
24 ``int ioctl(int fd, VIDIOC_S_PARM, v4l2_stream 24 ``int ioctl(int fd, VIDIOC_S_PARM, v4l2_streamparm *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 struct :c:type:`v4l2_streamparm 33 Pointer to struct :c:type:`v4l2_streamparm`.
34 34
35 Description 35 Description
36 =========== 36 ===========
37 37
38 Applications can request a different frame int 38 Applications can request a different frame interval. The capture or
39 output device will be reconfigured to support 39 output device will be reconfigured to support the requested frame
40 interval if possible. Optionally drivers may c 40 interval if possible. Optionally drivers may choose to skip or
41 repeat frames to achieve the requested frame i 41 repeat frames to achieve the requested frame interval.
42 42
43 For stateful encoders (see :ref:`encoder`) thi 43 For stateful encoders (see :ref:`encoder`) this represents the
44 frame interval that is typically embedded in t 44 frame interval that is typically embedded in the encoded video stream.
45 45
46 Changing the frame interval shall never change 46 Changing the frame interval shall never change the format. Changing the
47 format, on the other hand, may change the fram 47 format, on the other hand, may change the frame interval.
48 48
49 Further these ioctls can be used to determine 49 Further these ioctls can be used to determine the number of buffers used
50 internally by a driver in read/write mode. For 50 internally by a driver in read/write mode. For implications see the
51 section discussing the :c:func:`read()` functi 51 section discussing the :c:func:`read()` function.
52 52
53 To get and set the streaming parameters applic 53 To get and set the streaming parameters applications call the
54 :ref:`VIDIOC_G_PARM <VIDIOC_G_PARM>` and 54 :ref:`VIDIOC_G_PARM <VIDIOC_G_PARM>` and
55 :ref:`VIDIOC_S_PARM <VIDIOC_G_PARM>` ioctl, re 55 :ref:`VIDIOC_S_PARM <VIDIOC_G_PARM>` ioctl, respectively. They take a
56 pointer to a struct :c:type:`v4l2_streamparm` 56 pointer to a struct :c:type:`v4l2_streamparm` which contains a
57 union holding separate parameters for input an 57 union holding separate parameters for input and output devices.
58 58
59 .. tabularcolumns:: |p{3.7cm}|p{3.5cm}|p{10.1c 59 .. tabularcolumns:: |p{3.7cm}|p{3.5cm}|p{10.1cm}|
60 60
61 .. c:type:: v4l2_streamparm 61 .. c:type:: v4l2_streamparm
62 62
63 .. flat-table:: struct v4l2_streamparm 63 .. flat-table:: struct v4l2_streamparm
64 :header-rows: 0 64 :header-rows: 0
65 :stub-columns: 0 65 :stub-columns: 0
66 :widths: 1 1 2 66 :widths: 1 1 2
67 67
68 * - __u32 68 * - __u32
69 - ``type`` 69 - ``type``
70 - The buffer (stream) type, same as stru 70 - The buffer (stream) type, same as struct
71 :c:type:`v4l2_format` ``type``, set by 71 :c:type:`v4l2_format` ``type``, set by the
72 application. See :c:type:`v4l2_buf_typ 72 application. See :c:type:`v4l2_buf_type`.
73 * - union { 73 * - union {
74 - ``parm`` 74 - ``parm``
75 * - struct :c:type:`v4l2_captureparm` 75 * - struct :c:type:`v4l2_captureparm`
76 - ``capture`` 76 - ``capture``
77 - Parameters for capture devices, used w 77 - Parameters for capture devices, used when ``type`` is
78 ``V4L2_BUF_TYPE_VIDEO_CAPTURE`` or 78 ``V4L2_BUF_TYPE_VIDEO_CAPTURE`` or
79 ``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE`` 79 ``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE``.
80 * - struct :c:type:`v4l2_outputparm` 80 * - struct :c:type:`v4l2_outputparm`
81 - ``output`` 81 - ``output``
82 - Parameters for output devices, used wh 82 - Parameters for output devices, used when ``type`` is
83 ``V4L2_BUF_TYPE_VIDEO_OUTPUT`` or ``V4 83 ``V4L2_BUF_TYPE_VIDEO_OUTPUT`` or ``V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE``.
84 * - __u8 84 * - __u8
85 - ``raw_data``\ [200] 85 - ``raw_data``\ [200]
86 - A place holder for future extensions. 86 - A place holder for future extensions.
87 * - } 87 * - }
88 88
89 89
90 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm 90 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm}|
91 91
92 .. c:type:: v4l2_captureparm 92 .. c:type:: v4l2_captureparm
93 93
94 .. flat-table:: struct v4l2_captureparm 94 .. flat-table:: struct v4l2_captureparm
95 :header-rows: 0 95 :header-rows: 0
96 :stub-columns: 0 96 :stub-columns: 0
97 :widths: 1 1 2 97 :widths: 1 1 2
98 98
99 * - __u32 99 * - __u32
100 - ``capability`` 100 - ``capability``
101 - See :ref:`parm-caps`. 101 - See :ref:`parm-caps`.
102 * - __u32 102 * - __u32
103 - ``capturemode`` 103 - ``capturemode``
104 - Set by drivers and applications, see : 104 - Set by drivers and applications, see :ref:`parm-flags`.
105 * - struct :c:type:`v4l2_fract` 105 * - struct :c:type:`v4l2_fract`
106 - ``timeperframe`` 106 - ``timeperframe``
107 - This is the desired period between suc 107 - This is the desired period between successive frames captured by
108 the driver, in seconds. 108 the driver, in seconds.
109 * - :cspan:`2` 109 * - :cspan:`2`
110 110
111 This will configure the speed at which 111 This will configure the speed at which the video source (e.g. a sensor)
112 generates video frames. If the speed i 112 generates video frames. If the speed is fixed, then the driver may
113 choose to skip or repeat frames in ord 113 choose to skip or repeat frames in order to achieve the requested
114 frame rate. 114 frame rate.
115 115
116 For stateful encoders (see :ref:`encod 116 For stateful encoders (see :ref:`encoder`) this represents the
117 frame interval that is typically embed 117 frame interval that is typically embedded in the encoded video stream.
118 118
119 Applications store here the desired fr 119 Applications store here the desired frame period, drivers return
120 the actual frame period. 120 the actual frame period.
121 121
122 Changing the video standard (also impl 122 Changing the video standard (also implicitly by switching
123 the video input) may reset this parame 123 the video input) may reset this parameter to the nominal frame
124 period. To reset manually applications 124 period. To reset manually applications can just set this field to
125 zero. 125 zero.
126 126
127 Drivers support this function only whe 127 Drivers support this function only when they set the
128 ``V4L2_CAP_TIMEPERFRAME`` flag in the 128 ``V4L2_CAP_TIMEPERFRAME`` flag in the ``capability`` field.
129 * - __u32 129 * - __u32
130 - ``extendedmode`` 130 - ``extendedmode``
131 - Custom (driver specific) streaming par 131 - Custom (driver specific) streaming parameters. When unused,
132 applications and drivers must set this 132 applications and drivers must set this field to zero. Applications
133 using this field should check the driv 133 using this field should check the driver name and version, see
134 :ref:`querycap`. 134 :ref:`querycap`.
135 * - __u32 135 * - __u32
136 - ``readbuffers`` 136 - ``readbuffers``
137 - Applications set this field to the des 137 - Applications set this field to the desired number of buffers used
138 internally by the driver in :c:func:`r 138 internally by the driver in :c:func:`read()` mode.
139 Drivers return the actual number of bu 139 Drivers return the actual number of buffers. When an application
140 requests zero buffers, drivers should 140 requests zero buffers, drivers should just return the current
141 setting rather than the minimum or an 141 setting rather than the minimum or an error code. For details see
142 :ref:`rw`. 142 :ref:`rw`.
143 * - __u32 143 * - __u32
144 - ``reserved``\ [4] 144 - ``reserved``\ [4]
145 - Reserved for future extensions. Driver 145 - Reserved for future extensions. Drivers and applications must set
146 the array to zero. 146 the array to zero.
147 147
148 148
149 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm 149 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm}|
150 150
151 .. c:type:: v4l2_outputparm 151 .. c:type:: v4l2_outputparm
152 152
153 .. flat-table:: struct v4l2_outputparm 153 .. flat-table:: struct v4l2_outputparm
154 :header-rows: 0 154 :header-rows: 0
155 :stub-columns: 0 155 :stub-columns: 0
156 :widths: 1 1 2 156 :widths: 1 1 2
157 157
158 * - __u32 158 * - __u32
159 - ``capability`` 159 - ``capability``
160 - See :ref:`parm-caps`. 160 - See :ref:`parm-caps`.
161 * - __u32 161 * - __u32
162 - ``outputmode`` 162 - ``outputmode``
163 - Set by drivers and applications, see : 163 - Set by drivers and applications, see :ref:`parm-flags`.
164 * - struct :c:type:`v4l2_fract` 164 * - struct :c:type:`v4l2_fract`
165 - ``timeperframe`` 165 - ``timeperframe``
166 - This is the desired period between suc 166 - This is the desired period between successive frames output by the
167 driver, in seconds. 167 driver, in seconds.
168 * - :cspan:`2` 168 * - :cspan:`2`
169 169
170 The field is intended to repeat frames 170 The field is intended to repeat frames on the driver side in
171 :c:func:`write()` mode (in streaming m 171 :c:func:`write()` mode (in streaming mode timestamps
172 can be used to throttle the output), s 172 can be used to throttle the output), saving I/O bandwidth.
173 173
174 For stateful encoders (see :ref:`encod 174 For stateful encoders (see :ref:`encoder`) this represents the
175 frame interval that is typically embed 175 frame interval that is typically embedded in the encoded video stream
176 and it provides a hint to the encoder 176 and it provides a hint to the encoder of the speed at which raw
177 frames are queued up to the encoder. 177 frames are queued up to the encoder.
178 178
179 Applications store here the desired fr 179 Applications store here the desired frame period, drivers return
180 the actual frame period. 180 the actual frame period.
181 181
182 Changing the video standard (also impl 182 Changing the video standard (also implicitly by switching
183 the video output) may reset this param 183 the video output) may reset this parameter to the nominal frame
184 period. To reset manually applications 184 period. To reset manually applications can just set this field to
185 zero. 185 zero.
186 186
187 Drivers support this function only whe 187 Drivers support this function only when they set the
188 ``V4L2_CAP_TIMEPERFRAME`` flag in the 188 ``V4L2_CAP_TIMEPERFRAME`` flag in the ``capability`` field.
189 * - __u32 189 * - __u32
190 - ``extendedmode`` 190 - ``extendedmode``
191 - Custom (driver specific) streaming par 191 - Custom (driver specific) streaming parameters. When unused,
192 applications and drivers must set this 192 applications and drivers must set this field to zero. Applications
193 using this field should check the driv 193 using this field should check the driver name and version, see
194 :ref:`querycap`. 194 :ref:`querycap`.
195 * - __u32 195 * - __u32
196 - ``writebuffers`` 196 - ``writebuffers``
197 - Applications set this field to the des 197 - Applications set this field to the desired number of buffers used
198 internally by the driver in :c:func:`w 198 internally by the driver in :c:func:`write()` mode. Drivers
199 return the actual number of buffers. W 199 return the actual number of buffers. When an application requests
200 zero buffers, drivers should just retu 200 zero buffers, drivers should just return the current setting
201 rather than the minimum or an error co 201 rather than the minimum or an error code. For details see
202 :ref:`rw`. 202 :ref:`rw`.
203 * - __u32 203 * - __u32
204 - ``reserved``\ [4] 204 - ``reserved``\ [4]
205 - Reserved for future extensions. Driver 205 - Reserved for future extensions. Drivers and applications must set
206 the array to zero. 206 the array to zero.
207 207
208 208
209 .. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.5cm 209 .. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.5cm}|
210 210
211 .. _parm-caps: 211 .. _parm-caps:
212 212
213 .. flat-table:: Streaming Parameters Capabilit 213 .. flat-table:: Streaming Parameters Capabilities
214 :header-rows: 0 214 :header-rows: 0
215 :stub-columns: 0 215 :stub-columns: 0
216 :widths: 3 1 4 216 :widths: 3 1 4
217 217
218 * - ``V4L2_CAP_TIMEPERFRAME`` 218 * - ``V4L2_CAP_TIMEPERFRAME``
219 - 0x1000 219 - 0x1000
220 - The frame period can be modified by se 220 - The frame period can be modified by setting the ``timeperframe``
221 field. 221 field.
222 222
223 223
224 .. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.5cm 224 .. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.5cm}|
225 225
226 .. _parm-flags: 226 .. _parm-flags:
227 227
228 .. flat-table:: Capture Parameters Flags 228 .. flat-table:: Capture Parameters Flags
229 :header-rows: 0 229 :header-rows: 0
230 :stub-columns: 0 230 :stub-columns: 0
231 :widths: 3 1 4 231 :widths: 3 1 4
232 232
233 * - ``V4L2_MODE_HIGHQUALITY`` 233 * - ``V4L2_MODE_HIGHQUALITY``
234 - 0x0001 234 - 0x0001
235 - High quality imaging mode. High qualit 235 - High quality imaging mode. High quality mode is intended for still
236 imaging applications. The idea is to g 236 imaging applications. The idea is to get the best possible image
237 quality that the hardware can deliver. 237 quality that the hardware can deliver. It is not defined how the
238 driver writer may achieve that; it wil 238 driver writer may achieve that; it will depend on the hardware and
239 the ingenuity of the driver writer. Hi 239 the ingenuity of the driver writer. High quality mode is a
240 different mode from the regular motion 240 different mode from the regular motion video capture modes. In
241 high quality mode: 241 high quality mode:
242 242
243 - The driver may be able to capture h 243 - The driver may be able to capture higher resolutions than for
244 motion capture. 244 motion capture.
245 245
246 - The driver may support fewer pixel 246 - The driver may support fewer pixel formats than motion capture
247 (eg; true color). 247 (eg; true color).
248 248
249 - The driver may capture and arithmet 249 - The driver may capture and arithmetically combine multiple
250 successive fields or frames to remo 250 successive fields or frames to remove color edge artifacts and
251 reduce the noise in the video data. 251 reduce the noise in the video data.
252 252
253 - The driver may capture images in sl 253 - The driver may capture images in slices like a scanner in order
254 to handle larger format images than 254 to handle larger format images than would otherwise be
255 possible. 255 possible.
256 256
257 - An image capture operation may be s 257 - An image capture operation may be significantly slower than
258 motion capture. 258 motion capture.
259 259
260 - Moving objects in the image might h 260 - Moving objects in the image might have excessive motion blur.
261 261
262 - Capture might only work through the 262 - Capture might only work through the :c:func:`read()` call.
263 263
264 Return Value 264 Return Value
265 ============ 265 ============
266 266
267 On success 0 is returned, on error -1 and the 267 On success 0 is returned, on error -1 and the ``errno`` variable is set
268 appropriately. The generic error codes are des 268 appropriately. The generic error codes are described at the
269 :ref:`Generic Error Codes <gen-errors>` chapte 269 :ref:`Generic Error Codes <gen-errors>` chapter.
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