1 .. SPDX-License-Identifier: GFDL-1.1-no-invari
2 .. c:namespace:: V4L
3
4 .. _VIDIOC_DQEVENT:
5
6 ********************
7 ioctl VIDIOC_DQEVENT
8 ********************
9
10 Name
11 ====
12
13 VIDIOC_DQEVENT - Dequeue event
14
15 Synopsis
16 ========
17
18 .. c:macro:: VIDIOC_DQEVENT
19
20 ``int ioctl(int fd, VIDIOC_DQEVENT, struct v4l
21
22 Arguments
23 =========
24
25 ``fd``
26 File descriptor returned by :c:func:`open(
27
28 ``argp``
29 Pointer to struct :c:type:`v4l2_event`.
30
31 Description
32 ===========
33
34 Dequeue an event from a video device. No input
35 ioctl. All the fields of the struct :c:type:`v
36 structure are filled by the driver. The file h
37 exceptions which the application may get by e.
38 call.
39
40 .. c:type:: v4l2_event
41
42 .. tabularcolumns:: |p{3.0cm}|p{3.4cm}|p{10.9c
43
44
45 .. flat-table:: struct v4l2_event
46 :header-rows: 0
47 :stub-columns: 0
48 :widths: 1 1 2
49
50 * - __u32
51 - ``type``
52 - Type of the event, see :ref:`event-typ
53 * - union {
54 - ``u``
55 * - struct :c:type:`v4l2_event_vsync`
56 - ``vsync``
57 - Event data for event ``V4L2_EVENT_VSYN
58 * - struct :c:type:`v4l2_event_ctrl`
59 - ``ctrl``
60 - Event data for event ``V4L2_EVENT_CTRL
61 * - struct :c:type:`v4l2_event_frame_sync`
62 - ``frame_sync``
63 - Event data for event ``V4L2_EVENT_FRAM
64 * - struct :c:type:`v4l2_event_motion_det`
65 - ``motion_det``
66 - Event data for event V4L2_EVENT_MOTION
67 * - struct :c:type:`v4l2_event_src_change`
68 - ``src_change``
69 - Event data for event V4L2_EVENT_SOURCE
70 * - __u8
71 - ``data``\ [64]
72 - Event data. Defined by the event type.
73 define easily accessible type for even
74 * - }
75 -
76 * - __u32
77 - ``pending``
78 - Number of pending events excluding thi
79 * - __u32
80 - ``sequence``
81 - Event sequence number. The sequence nu
82 every subscribed event that takes plac
83 not contiguous it means that events ha
84 * - struct timespec
85 - ``timestamp``
86 - Event timestamp. The timestamp has bee
87 ``CLOCK_MONOTONIC`` clock. To access t
88 use :c:func:`clock_gettime`.
89 * - u32
90 - ``id``
91 - The ID associated with the event sourc
92 have an associated ID (this depends on
93 is 0.
94 * - __u32
95 - ``reserved``\ [8]
96 - Reserved for future extensions. Driver
97 zero.
98
99
100 .. tabularcolumns:: |p{6.2cm}|p{2.6cm}|p{8.5cm
101
102 .. cssclass:: longtable
103
104 .. _event-type:
105
106 .. flat-table:: Event Types
107 :header-rows: 0
108 :stub-columns: 0
109 :widths: 3 1 4
110
111 * - ``V4L2_EVENT_ALL``
112 - 0
113 - All events. V4L2_EVENT_ALL is valid on
114 VIDIOC_UNSUBSCRIBE_EVENT for unsubscri
115 * - ``V4L2_EVENT_VSYNC``
116 - 1
117 - This event is triggered on the vertica
118 struct :c:type:`v4l2_event_vsync` asso
119 with it.
120 * - ``V4L2_EVENT_EOS``
121 - 2
122 - This event is triggered when the end o
123 is typically used with MPEG decoders t
124 when the last of the MPEG stream has b
125 * - ``V4L2_EVENT_CTRL``
126 - 3
127 - This event requires that the ``id`` ma
128 which you want to receive events. This
129 control's value changes, if a button c
130 control's flags change. This event has
131 :c:type:`v4l2_event_ctrl` associated w
132 This struct contains much of the same
133 :ref:`v4l2_queryctrl <v4l2-queryctrl>`
134 :c:type:`v4l2_control`.
135
136 If the event is generated due to a cal
137 :ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` o
138 :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT
139 event will *not* be sent to the file h
140 function. This prevents nasty feedback
141 get the event, then set the ``V4L2_EVE
142 flag.
143
144 This event type will ensure that no in
145 events are raised than there is room i
146 struct :c:type:`v4l2_event_ctrl` of th
147 second-oldest event is kept, but the `
148 second-oldest event is ORed with the `
149 oldest event.
150 * - ``V4L2_EVENT_FRAME_SYNC``
151 - 4
152 - Triggered immediately when the recepti
153 This event has a struct
154 :c:type:`v4l2_event_frame_sync`
155 associated with it.
156
157 If the hardware needs to be stopped in
158 underrun it might not be able to gener
159 cases the ``frame_sequence`` field in
160 :c:type:`v4l2_event_frame_sync` will n
161 be incremented. This causes two consec
162 to have n times frame interval in betw
163 * - ``V4L2_EVENT_SOURCE_CHANGE``
164 - 5
165 - This event is triggered when a source
166 during runtime by the video device. It
167 change triggered by a video decoder or
168 on an input connector. This event requ
169 the input index (when used with a vide
170 index (when used with a subdevice node
171 receive events.
172
173 This event has a struct
174 :c:type:`v4l2_event_src_change`
175 associated with it. The ``changes`` bi
176 changed for the subscribed pad. If mul
177 application could dequeue them, then t
178 ORed value of all the events generated
179 * - ``V4L2_EVENT_MOTION_DET``
180 - 6
181 - Triggered whenever the motion detectio
182 the regions changes. This event has a
183 :c:type:`v4l2_event_motion_det`
184 associated with it.
185 * - ``V4L2_EVENT_PRIVATE_START``
186 - 0x08000000
187 - Base event number for driver-private e
188
189
190 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm
191
192 .. c:type:: v4l2_event_vsync
193
194 .. flat-table:: struct v4l2_event_vsync
195 :header-rows: 0
196 :stub-columns: 0
197 :widths: 1 1 2
198
199 * - __u8
200 - ``field``
201 - The upcoming field. See enum :c:type:`
202
203
204 .. tabularcolumns:: |p{3.5cm}|p{3.0cm}|p{10.8c
205
206 .. c:type:: v4l2_event_ctrl
207
208 .. flat-table:: struct v4l2_event_ctrl
209 :header-rows: 0
210 :stub-columns: 0
211 :widths: 1 1 2
212
213 * - __u32
214 - ``changes``
215 - A bitmask that tells what has changed.
216 :ref:`ctrl-changes-flags`.
217 * - __u32
218 - ``type``
219 - The type of the control. See enum
220 :c:type:`v4l2_ctrl_type`.
221 * - union {
222 - (anonymous)
223 * - __s32
224 - ``value``
225 - The 32-bit value of the control for 32
226 0 for string controls since the value
227 using :ref:`VIDIOC_DQEVENT`.
228 * - __s64
229 - ``value64``
230 - The 64-bit value of the control for 64
231 * - }
232 -
233 * - __u32
234 - ``flags``
235 - The control flags. See :ref:`control-f
236 * - __s32
237 - ``minimum``
238 - The minimum value of the control. See
239 :ref:`v4l2_queryctrl <v4l2-queryctrl>`
240 * - __s32
241 - ``maximum``
242 - The maximum value of the control. See
243 :ref:`v4l2_queryctrl <v4l2-queryctrl>`
244 * - __s32
245 - ``step``
246 - The step value of the control. See str
247 :ref:`v4l2_queryctrl <v4l2-queryctrl>`
248 * - __s32
249 - ``default_value``
250 - The default value of the control. See
251 :ref:`v4l2_queryctrl <v4l2-queryctrl>`
252
253
254 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm
255
256 .. c:type:: v4l2_event_frame_sync
257
258 .. flat-table:: struct v4l2_event_frame_sync
259 :header-rows: 0
260 :stub-columns: 0
261 :widths: 1 1 2
262
263 * - __u32
264 - ``frame_sequence``
265 - The sequence number of the frame being
266
267
268 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm
269
270 .. c:type:: v4l2_event_src_change
271
272 .. flat-table:: struct v4l2_event_src_change
273 :header-rows: 0
274 :stub-columns: 0
275 :widths: 1 1 2
276
277 * - __u32
278 - ``changes``
279 - A bitmask that tells what has changed.
280 :ref:`src-changes-flags`.
281
282
283 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm
284
285 .. c:type:: v4l2_event_motion_det
286
287 .. flat-table:: struct v4l2_event_motion_det
288 :header-rows: 0
289 :stub-columns: 0
290 :widths: 1 1 2
291
292 * - __u32
293 - ``flags``
294 - Currently only one flag is available:
295 ``V4L2_EVENT_MD_FL_HAVE_FRAME_SEQ`` is
296 ``frame_sequence`` field is valid, oth
297 ignored.
298 * - __u32
299 - ``frame_sequence``
300 - The sequence number of the frame being
301 ``V4L2_EVENT_MD_FL_HAVE_FRAME_SEQ`` fl
302 * - __u32
303 - ``region_mask``
304 - The bitmask of the regions that report
305 one region. If this field is 0, then n
306 all. If there is no ``V4L2_CID_DETECT_
307 (see :ref:`detect-controls`) to assign
308 each cell in the motion detection grid
309 automatically assigned to the default
310
311
312 .. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.5cm
313
314 .. _ctrl-changes-flags:
315
316 .. flat-table:: Control Changes
317 :header-rows: 0
318 :stub-columns: 0
319 :widths: 3 1 4
320
321 * - ``V4L2_EVENT_CTRL_CH_VALUE``
322 - 0x0001
323 - This control event was triggered becau
324 changed. Special cases: Volatile contr
325 event; If a control has the ``V4L2_CTR
326 flag set, then this event is sent as w
327 * - ``V4L2_EVENT_CTRL_CH_FLAGS``
328 - 0x0002
329 - This control event was triggered becau
330 changed.
331 * - ``V4L2_EVENT_CTRL_CH_RANGE``
332 - 0x0004
333 - This control event was triggered becau
334 step or the default value of the contr
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
341
342 .. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.5cm
343
344 .. _src-changes-flags:
345
346 .. flat-table:: Source Changes
347 :header-rows: 0
348 :stub-columns: 0
349 :widths: 3 1 4
350
351 * - ``V4L2_EVENT_SRC_CH_RESOLUTION``
352 - 0x0001
353 - This event gets triggered when a resol
354 an input. This can come from an input
355 decoder. Applications will have to que
356 any, the signal may also have been los
357
358 For stateful decoders follow the guide
359 Video Capture devices have to query th
360 :ref:`VIDIOC_QUERY_DV_TIMINGS` or
361 :ref:`VIDIOC_QUERYSTD <VIDIOC_QUERYSTD
362
363 *Important*: even if the new video tim
364 ones, receiving this event indicates t
365 video signal and you must stop and res
366 (:ref:`VIDIOC_STREAMOFF <VIDIOC_STREAM
367 followed by :ref:`VIDIOC_STREAMON <VID
368 that many Video Capture devices are no
369 loss of signal and so restarting strea
370 the hardware to synchronize to the vid
371
372 Return Value
373 ============
374
375 On success 0 is returned, on error -1 and the
376 appropriately. The generic error codes are des
377 :ref:`Generic Error Codes <gen-errors>` chapte
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