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_DQEVENT: 4 .. _VIDIOC_DQEVENT:
5 5
6 ******************** 6 ********************
7 ioctl VIDIOC_DQEVENT 7 ioctl VIDIOC_DQEVENT
8 ******************** 8 ********************
9 9
10 Name 10 Name
11 ==== 11 ====
12 12
13 VIDIOC_DQEVENT - Dequeue event 13 VIDIOC_DQEVENT - Dequeue event
14 14
15 Synopsis 15 Synopsis
16 ======== 16 ========
17 17
18 .. c:macro:: VIDIOC_DQEVENT 18 .. c:macro:: VIDIOC_DQEVENT
19 19
20 ``int ioctl(int fd, VIDIOC_DQEVENT, struct v4l 20 ``int ioctl(int fd, VIDIOC_DQEVENT, struct v4l2_event *argp)``
21 21
22 Arguments 22 Arguments
23 ========= 23 =========
24 24
25 ``fd`` 25 ``fd``
26 File descriptor returned by :c:func:`open( 26 File descriptor returned by :c:func:`open()`.
27 27
28 ``argp`` 28 ``argp``
29 Pointer to struct :c:type:`v4l2_event`. 29 Pointer to struct :c:type:`v4l2_event`.
30 30
31 Description 31 Description
32 =========== 32 ===========
33 33
34 Dequeue an event from a video device. No input 34 Dequeue an event from a video device. No input is required for this
35 ioctl. All the fields of the struct :c:type:`v 35 ioctl. All the fields of the struct :c:type:`v4l2_event`
36 structure are filled by the driver. The file h 36 structure are filled by the driver. The file handle will also receive
37 exceptions which the application may get by e. 37 exceptions which the application may get by e.g. using the select system
38 call. 38 call.
39 39
40 .. c:type:: v4l2_event !! 40 .. tabularcolumns:: |p{3.0cm}|p{4.4cm}|p{2.4cm}|p{7.7cm}|
41 41
42 .. tabularcolumns:: |p{3.0cm}|p{3.4cm}|p{10.9c !! 42 .. c:type:: v4l2_event
43 43
>> 44 .. cssclass: longtable
44 45
45 .. flat-table:: struct v4l2_event 46 .. flat-table:: struct v4l2_event
46 :header-rows: 0 47 :header-rows: 0
47 :stub-columns: 0 48 :stub-columns: 0
48 :widths: 1 1 2 49 :widths: 1 1 2
49 50
50 * - __u32 51 * - __u32
51 - ``type`` 52 - ``type``
52 - Type of the event, see :ref:`event-typ 53 - Type of the event, see :ref:`event-type`.
53 * - union { 54 * - union {
54 - ``u`` 55 - ``u``
55 * - struct :c:type:`v4l2_event_vsync` 56 * - struct :c:type:`v4l2_event_vsync`
56 - ``vsync`` 57 - ``vsync``
57 - Event data for event ``V4L2_EVENT_VSYN 58 - Event data for event ``V4L2_EVENT_VSYNC``.
58 * - struct :c:type:`v4l2_event_ctrl` 59 * - struct :c:type:`v4l2_event_ctrl`
59 - ``ctrl`` 60 - ``ctrl``
60 - Event data for event ``V4L2_EVENT_CTRL 61 - Event data for event ``V4L2_EVENT_CTRL``.
61 * - struct :c:type:`v4l2_event_frame_sync` 62 * - struct :c:type:`v4l2_event_frame_sync`
62 - ``frame_sync`` 63 - ``frame_sync``
63 - Event data for event ``V4L2_EVENT_FRAM 64 - Event data for event ``V4L2_EVENT_FRAME_SYNC``.
64 * - struct :c:type:`v4l2_event_motion_det` 65 * - struct :c:type:`v4l2_event_motion_det`
65 - ``motion_det`` 66 - ``motion_det``
66 - Event data for event V4L2_EVENT_MOTION 67 - Event data for event V4L2_EVENT_MOTION_DET.
67 * - struct :c:type:`v4l2_event_src_change` 68 * - struct :c:type:`v4l2_event_src_change`
68 - ``src_change`` 69 - ``src_change``
69 - Event data for event V4L2_EVENT_SOURCE 70 - Event data for event V4L2_EVENT_SOURCE_CHANGE.
70 * - __u8 71 * - __u8
71 - ``data``\ [64] 72 - ``data``\ [64]
72 - Event data. Defined by the event type. 73 - Event data. Defined by the event type. The union should be used to
73 define easily accessible type for even 74 define easily accessible type for events.
74 * - } 75 * - }
75 - 76 -
76 * - __u32 77 * - __u32
77 - ``pending`` 78 - ``pending``
78 - Number of pending events excluding thi 79 - Number of pending events excluding this one.
79 * - __u32 80 * - __u32
80 - ``sequence`` 81 - ``sequence``
81 - Event sequence number. The sequence nu 82 - Event sequence number. The sequence number is incremented for
82 every subscribed event that takes plac 83 every subscribed event that takes place. If sequence numbers are
83 not contiguous it means that events ha 84 not contiguous it means that events have been lost.
84 * - struct timespec 85 * - struct timespec
85 - ``timestamp`` 86 - ``timestamp``
86 - Event timestamp. The timestamp has bee 87 - Event timestamp. The timestamp has been taken from the
87 ``CLOCK_MONOTONIC`` clock. To access t 88 ``CLOCK_MONOTONIC`` clock. To access the same clock outside V4L2,
88 use :c:func:`clock_gettime`. 89 use :c:func:`clock_gettime`.
89 * - u32 90 * - u32
90 - ``id`` 91 - ``id``
91 - The ID associated with the event sourc 92 - The ID associated with the event source. If the event does not
92 have an associated ID (this depends on 93 have an associated ID (this depends on the event type), then this
93 is 0. 94 is 0.
94 * - __u32 95 * - __u32
95 - ``reserved``\ [8] 96 - ``reserved``\ [8]
96 - Reserved for future extensions. Driver 97 - Reserved for future extensions. Drivers must set the array to
97 zero. 98 zero.
98 99
99 100
100 .. tabularcolumns:: |p{6.2cm}|p{2.6cm}|p{8.5cm !! 101 .. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}|
101 102
102 .. cssclass:: longtable 103 .. cssclass:: longtable
103 104
104 .. _event-type: 105 .. _event-type:
105 106
106 .. flat-table:: Event Types 107 .. flat-table:: Event Types
107 :header-rows: 0 108 :header-rows: 0
108 :stub-columns: 0 109 :stub-columns: 0
109 :widths: 3 1 4 110 :widths: 3 1 4
110 111
111 * - ``V4L2_EVENT_ALL`` 112 * - ``V4L2_EVENT_ALL``
112 - 0 113 - 0
113 - All events. V4L2_EVENT_ALL is valid on 114 - All events. V4L2_EVENT_ALL is valid only for
114 VIDIOC_UNSUBSCRIBE_EVENT for unsubscri 115 VIDIOC_UNSUBSCRIBE_EVENT for unsubscribing all events at once.
115 * - ``V4L2_EVENT_VSYNC`` 116 * - ``V4L2_EVENT_VSYNC``
116 - 1 117 - 1
117 - This event is triggered on the vertica 118 - This event is triggered on the vertical sync. This event has a
118 struct :c:type:`v4l2_event_vsync` asso 119 struct :c:type:`v4l2_event_vsync` associated
119 with it. 120 with it.
120 * - ``V4L2_EVENT_EOS`` 121 * - ``V4L2_EVENT_EOS``
121 - 2 122 - 2
122 - This event is triggered when the end o 123 - This event is triggered when the end of a stream is reached. This
123 is typically used with MPEG decoders t 124 is typically used with MPEG decoders to report to the application
124 when the last of the MPEG stream has b 125 when the last of the MPEG stream has been decoded.
125 * - ``V4L2_EVENT_CTRL`` 126 * - ``V4L2_EVENT_CTRL``
126 - 3 127 - 3
127 - This event requires that the ``id`` ma 128 - This event requires that the ``id`` matches the control ID from
128 which you want to receive events. This 129 which you want to receive events. This event is triggered if the
129 control's value changes, if a button c 130 control's value changes, if a button control is pressed or if the
130 control's flags change. This event has 131 control's flags change. This event has a struct
131 :c:type:`v4l2_event_ctrl` associated w 132 :c:type:`v4l2_event_ctrl` associated with it.
132 This struct contains much of the same 133 This struct contains much of the same information as struct
133 :ref:`v4l2_queryctrl <v4l2-queryctrl>` 134 :ref:`v4l2_queryctrl <v4l2-queryctrl>` and struct
134 :c:type:`v4l2_control`. 135 :c:type:`v4l2_control`.
135 136
136 If the event is generated due to a cal 137 If the event is generated due to a call to
137 :ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` o 138 :ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` or
138 :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT 139 :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>`, then the
139 event will *not* be sent to the file h 140 event will *not* be sent to the file handle that called the ioctl
140 function. This prevents nasty feedback 141 function. This prevents nasty feedback loops. If you *do* want to
141 get the event, then set the ``V4L2_EVE 142 get the event, then set the ``V4L2_EVENT_SUB_FL_ALLOW_FEEDBACK``
142 flag. 143 flag.
143 144
144 This event type will ensure that no in 145 This event type will ensure that no information is lost when more
145 events are raised than there is room i 146 events are raised than there is room internally. In that case the
146 struct :c:type:`v4l2_event_ctrl` of th 147 struct :c:type:`v4l2_event_ctrl` of the
147 second-oldest event is kept, but the ` 148 second-oldest event is kept, but the ``changes`` field of the
148 second-oldest event is ORed with the ` 149 second-oldest event is ORed with the ``changes`` field of the
149 oldest event. 150 oldest event.
150 * - ``V4L2_EVENT_FRAME_SYNC`` 151 * - ``V4L2_EVENT_FRAME_SYNC``
151 - 4 152 - 4
152 - Triggered immediately when the recepti 153 - Triggered immediately when the reception of a frame has begun.
153 This event has a struct 154 This event has a struct
154 :c:type:`v4l2_event_frame_sync` 155 :c:type:`v4l2_event_frame_sync`
155 associated with it. 156 associated with it.
156 157
157 If the hardware needs to be stopped in 158 If the hardware needs to be stopped in the case of a buffer
158 underrun it might not be able to gener 159 underrun it might not be able to generate this event. In such
159 cases the ``frame_sequence`` field in 160 cases the ``frame_sequence`` field in struct
160 :c:type:`v4l2_event_frame_sync` will n 161 :c:type:`v4l2_event_frame_sync` will not
161 be incremented. This causes two consec 162 be incremented. This causes two consecutive frame sequence numbers
162 to have n times frame interval in betw 163 to have n times frame interval in between them.
163 * - ``V4L2_EVENT_SOURCE_CHANGE`` 164 * - ``V4L2_EVENT_SOURCE_CHANGE``
164 - 5 165 - 5
165 - This event is triggered when a source 166 - This event is triggered when a source parameter change is detected
166 during runtime by the video device. It 167 during runtime by the video device. It can be a runtime resolution
167 change triggered by a video decoder or 168 change triggered by a video decoder or the format change happening
168 on an input connector. This event requ 169 on an input connector. This event requires that the ``id`` matches
169 the input index (when used with a vide 170 the input index (when used with a video device node) or the pad
170 index (when used with a subdevice node 171 index (when used with a subdevice node) from which you want to
171 receive events. 172 receive events.
172 173
173 This event has a struct 174 This event has a struct
174 :c:type:`v4l2_event_src_change` 175 :c:type:`v4l2_event_src_change`
175 associated with it. The ``changes`` bi 176 associated with it. The ``changes`` bitfield denotes what has
176 changed for the subscribed pad. If mul 177 changed for the subscribed pad. If multiple events occurred before
177 application could dequeue them, then t 178 application could dequeue them, then the changes will have the
178 ORed value of all the events generated 179 ORed value of all the events generated.
179 * - ``V4L2_EVENT_MOTION_DET`` 180 * - ``V4L2_EVENT_MOTION_DET``
180 - 6 181 - 6
181 - Triggered whenever the motion detectio 182 - Triggered whenever the motion detection state for one or more of
182 the regions changes. This event has a 183 the regions changes. This event has a struct
183 :c:type:`v4l2_event_motion_det` 184 :c:type:`v4l2_event_motion_det`
184 associated with it. 185 associated with it.
185 * - ``V4L2_EVENT_PRIVATE_START`` 186 * - ``V4L2_EVENT_PRIVATE_START``
186 - 0x08000000 187 - 0x08000000
187 - Base event number for driver-private e 188 - Base event number for driver-private events.
188 189
189 190
190 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm !! 191 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
191 192
192 .. c:type:: v4l2_event_vsync 193 .. c:type:: v4l2_event_vsync
193 194
194 .. flat-table:: struct v4l2_event_vsync 195 .. flat-table:: struct v4l2_event_vsync
195 :header-rows: 0 196 :header-rows: 0
196 :stub-columns: 0 197 :stub-columns: 0
197 :widths: 1 1 2 198 :widths: 1 1 2
198 199
199 * - __u8 200 * - __u8
200 - ``field`` 201 - ``field``
201 - The upcoming field. See enum :c:type:` 202 - The upcoming field. See enum :c:type:`v4l2_field`.
202 203
203 204
204 .. tabularcolumns:: |p{3.5cm}|p{3.0cm}|p{10.8c !! 205 .. tabularcolumns:: |p{3.5cm}|p{3.0cm}|p{1.8cm}|p{8.5cm}|
205 206
206 .. c:type:: v4l2_event_ctrl 207 .. c:type:: v4l2_event_ctrl
207 208
208 .. flat-table:: struct v4l2_event_ctrl 209 .. flat-table:: struct v4l2_event_ctrl
209 :header-rows: 0 210 :header-rows: 0
210 :stub-columns: 0 211 :stub-columns: 0
211 :widths: 1 1 2 212 :widths: 1 1 2
212 213
213 * - __u32 214 * - __u32
214 - ``changes`` 215 - ``changes``
215 - A bitmask that tells what has changed. 216 - A bitmask that tells what has changed. See
216 :ref:`ctrl-changes-flags`. 217 :ref:`ctrl-changes-flags`.
217 * - __u32 218 * - __u32
218 - ``type`` 219 - ``type``
219 - The type of the control. See enum 220 - The type of the control. See enum
220 :c:type:`v4l2_ctrl_type`. 221 :c:type:`v4l2_ctrl_type`.
221 * - union { 222 * - union {
222 - (anonymous) 223 - (anonymous)
223 * - __s32 224 * - __s32
224 - ``value`` 225 - ``value``
225 - The 32-bit value of the control for 32 226 - The 32-bit value of the control for 32-bit control types. This is
226 0 for string controls since the value 227 0 for string controls since the value of a string cannot be passed
227 using :ref:`VIDIOC_DQEVENT`. 228 using :ref:`VIDIOC_DQEVENT`.
228 * - __s64 229 * - __s64
229 - ``value64`` 230 - ``value64``
230 - The 64-bit value of the control for 64 231 - The 64-bit value of the control for 64-bit control types.
231 * - } 232 * - }
232 - 233 -
233 * - __u32 234 * - __u32
234 - ``flags`` 235 - ``flags``
235 - The control flags. See :ref:`control-f 236 - The control flags. See :ref:`control-flags`.
236 * - __s32 237 * - __s32
237 - ``minimum`` 238 - ``minimum``
238 - The minimum value of the control. See 239 - The minimum value of the control. See struct
239 :ref:`v4l2_queryctrl <v4l2-queryctrl>` 240 :ref:`v4l2_queryctrl <v4l2-queryctrl>`.
240 * - __s32 241 * - __s32
241 - ``maximum`` 242 - ``maximum``
242 - The maximum value of the control. See 243 - The maximum value of the control. See struct
243 :ref:`v4l2_queryctrl <v4l2-queryctrl>` 244 :ref:`v4l2_queryctrl <v4l2-queryctrl>`.
244 * - __s32 245 * - __s32
245 - ``step`` 246 - ``step``
246 - The step value of the control. See str 247 - The step value of the control. See struct
247 :ref:`v4l2_queryctrl <v4l2-queryctrl>` 248 :ref:`v4l2_queryctrl <v4l2-queryctrl>`.
248 * - __s32 249 * - __s32
249 - ``default_value`` 250 - ``default_value``
250 - The default value of the control. See 251 - The default value of the control. See struct
251 :ref:`v4l2_queryctrl <v4l2-queryctrl>` 252 :ref:`v4l2_queryctrl <v4l2-queryctrl>`.
252 253
253 254
254 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm !! 255 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
255 256
256 .. c:type:: v4l2_event_frame_sync 257 .. c:type:: v4l2_event_frame_sync
257 258
258 .. flat-table:: struct v4l2_event_frame_sync 259 .. flat-table:: struct v4l2_event_frame_sync
259 :header-rows: 0 260 :header-rows: 0
260 :stub-columns: 0 261 :stub-columns: 0
261 :widths: 1 1 2 262 :widths: 1 1 2
262 263
263 * - __u32 264 * - __u32
264 - ``frame_sequence`` 265 - ``frame_sequence``
265 - The sequence number of the frame being 266 - The sequence number of the frame being received.
266 267
267 268
268 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm !! 269 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
269 270
270 .. c:type:: v4l2_event_src_change 271 .. c:type:: v4l2_event_src_change
271 272
272 .. flat-table:: struct v4l2_event_src_change 273 .. flat-table:: struct v4l2_event_src_change
273 :header-rows: 0 274 :header-rows: 0
274 :stub-columns: 0 275 :stub-columns: 0
275 :widths: 1 1 2 276 :widths: 1 1 2
276 277
277 * - __u32 278 * - __u32
278 - ``changes`` 279 - ``changes``
279 - A bitmask that tells what has changed. 280 - A bitmask that tells what has changed. See
280 :ref:`src-changes-flags`. 281 :ref:`src-changes-flags`.
281 282
282 283
283 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm !! 284 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
284 285
285 .. c:type:: v4l2_event_motion_det 286 .. c:type:: v4l2_event_motion_det
286 287
287 .. flat-table:: struct v4l2_event_motion_det 288 .. flat-table:: struct v4l2_event_motion_det
288 :header-rows: 0 289 :header-rows: 0
289 :stub-columns: 0 290 :stub-columns: 0
290 :widths: 1 1 2 291 :widths: 1 1 2
291 292
292 * - __u32 293 * - __u32
293 - ``flags`` 294 - ``flags``
294 - Currently only one flag is available: 295 - Currently only one flag is available: if
295 ``V4L2_EVENT_MD_FL_HAVE_FRAME_SEQ`` is 296 ``V4L2_EVENT_MD_FL_HAVE_FRAME_SEQ`` is set, then the
296 ``frame_sequence`` field is valid, oth 297 ``frame_sequence`` field is valid, otherwise that field should be
297 ignored. 298 ignored.
298 * - __u32 299 * - __u32
299 - ``frame_sequence`` 300 - ``frame_sequence``
300 - The sequence number of the frame being 301 - The sequence number of the frame being received. Only valid if the
301 ``V4L2_EVENT_MD_FL_HAVE_FRAME_SEQ`` fl 302 ``V4L2_EVENT_MD_FL_HAVE_FRAME_SEQ`` flag was set.
302 * - __u32 303 * - __u32
303 - ``region_mask`` 304 - ``region_mask``
304 - The bitmask of the regions that report 305 - The bitmask of the regions that reported motion. There is at least
305 one region. If this field is 0, then n 306 one region. If this field is 0, then no motion was detected at
306 all. If there is no ``V4L2_CID_DETECT_ 307 all. If there is no ``V4L2_CID_DETECT_MD_REGION_GRID`` control
307 (see :ref:`detect-controls`) to assign 308 (see :ref:`detect-controls`) to assign a different region to
308 each cell in the motion detection grid 309 each cell in the motion detection grid, then that all cells are
309 automatically assigned to the default 310 automatically assigned to the default region 0.
310 311
311 312
312 .. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.5cm !! 313 .. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}|
313 314
314 .. _ctrl-changes-flags: 315 .. _ctrl-changes-flags:
315 316
316 .. flat-table:: Control Changes 317 .. flat-table:: Control Changes
317 :header-rows: 0 318 :header-rows: 0
318 :stub-columns: 0 319 :stub-columns: 0
319 :widths: 3 1 4 320 :widths: 3 1 4
320 321
321 * - ``V4L2_EVENT_CTRL_CH_VALUE`` 322 * - ``V4L2_EVENT_CTRL_CH_VALUE``
322 - 0x0001 323 - 0x0001
323 - This control event was triggered becau 324 - This control event was triggered because the value of the control
324 changed. Special cases: Volatile contr 325 changed. Special cases: Volatile controls do no generate this
325 event; If a control has the ``V4L2_CTR 326 event; If a control has the ``V4L2_CTRL_FLAG_EXECUTE_ON_WRITE``
326 flag set, then this event is sent as w 327 flag set, then this event is sent as well, regardless its value.
327 * - ``V4L2_EVENT_CTRL_CH_FLAGS`` 328 * - ``V4L2_EVENT_CTRL_CH_FLAGS``
328 - 0x0002 329 - 0x0002
329 - This control event was triggered becau 330 - This control event was triggered because the control flags
330 changed. 331 changed.
331 * - ``V4L2_EVENT_CTRL_CH_RANGE`` 332 * - ``V4L2_EVENT_CTRL_CH_RANGE``
332 - 0x0004 333 - 0x0004
333 - This control event was triggered becau 334 - This control event was triggered because the minimum, maximum,
334 step or the default value of the contr 335 step or the default value of the control changed.
335 * - ``V4L2_EVENT_CTRL_CH_DIMENSIONS`` <<
336 - 0x0008 <<
337 - This control event was triggered becau <<
338 control changed. Note that the number <<
339 same. <<
340 336
341 337
342 .. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.5cm !! 338 .. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}|
343 339
344 .. _src-changes-flags: 340 .. _src-changes-flags:
345 341
346 .. flat-table:: Source Changes 342 .. flat-table:: Source Changes
347 :header-rows: 0 343 :header-rows: 0
348 :stub-columns: 0 344 :stub-columns: 0
349 :widths: 3 1 4 345 :widths: 3 1 4
350 346
351 * - ``V4L2_EVENT_SRC_CH_RESOLUTION`` 347 * - ``V4L2_EVENT_SRC_CH_RESOLUTION``
352 - 0x0001 348 - 0x0001
353 - This event gets triggered when a resol 349 - This event gets triggered when a resolution change is detected at
354 an input. This can come from an input 350 an input. This can come from an input connector or from a video
355 decoder. Applications will have to que 351 decoder. Applications will have to query the new resolution (if
356 any, the signal may also have been los 352 any, the signal may also have been lost).
357 353
358 For stateful decoders follow the guide 354 For stateful decoders follow the guidelines in :ref:`decoder`.
359 Video Capture devices have to query th 355 Video Capture devices have to query the new timings using
360 :ref:`VIDIOC_QUERY_DV_TIMINGS` or 356 :ref:`VIDIOC_QUERY_DV_TIMINGS` or
361 :ref:`VIDIOC_QUERYSTD <VIDIOC_QUERYSTD 357 :ref:`VIDIOC_QUERYSTD <VIDIOC_QUERYSTD>`.
362 358
363 *Important*: even if the new video tim 359 *Important*: even if the new video timings appear identical to the old
364 ones, receiving this event indicates t 360 ones, receiving this event indicates that there was an issue with the
365 video signal and you must stop and res 361 video signal and you must stop and restart streaming
366 (:ref:`VIDIOC_STREAMOFF <VIDIOC_STREAM 362 (:ref:`VIDIOC_STREAMOFF <VIDIOC_STREAMON>`
367 followed by :ref:`VIDIOC_STREAMON <VID 363 followed by :ref:`VIDIOC_STREAMON <VIDIOC_STREAMON>`). The reason is
368 that many Video Capture devices are no 364 that many Video Capture devices are not able to recover from a temporary
369 loss of signal and so restarting strea 365 loss of signal and so restarting streaming I/O is required in order for
370 the hardware to synchronize to the vid 366 the hardware to synchronize to the video signal.
371 367
372 Return Value 368 Return Value
373 ============ 369 ============
374 370
375 On success 0 is returned, on error -1 and the 371 On success 0 is returned, on error -1 and the ``errno`` variable is set
376 appropriately. The generic error codes are des 372 appropriately. The generic error codes are described at the
377 :ref:`Generic Error Codes <gen-errors>` chapte 373 :ref:`Generic Error Codes <gen-errors>` chapter.
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.