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1 | <refentry id="vidioc-g-parm"> |
2 | <refmeta> | |
3 | <refentrytitle>ioctl VIDIOC_G_PARM, VIDIOC_S_PARM</refentrytitle> | |
4 | &manvol; | |
5 | </refmeta> | |
6 | ||
7 | <refnamediv> | |
8 | <refname>VIDIOC_G_PARM</refname> | |
9 | <refname>VIDIOC_S_PARM</refname> | |
10 | <refpurpose>Get or set streaming parameters</refpurpose> | |
11 | </refnamediv> | |
12 | ||
13 | <refsynopsisdiv> | |
14 | <funcsynopsis> | |
15 | <funcprototype> | |
16 | <funcdef>int <function>ioctl</function></funcdef> | |
17 | <paramdef>int <parameter>fd</parameter></paramdef> | |
18 | <paramdef>int <parameter>request</parameter></paramdef> | |
19 | <paramdef>v4l2_streamparm *<parameter>argp</parameter></paramdef> | |
20 | </funcprototype> | |
21 | </funcsynopsis> | |
22 | </refsynopsisdiv> | |
23 | ||
24 | <refsect1> | |
25 | <title>Arguments</title> | |
26 | ||
27 | <variablelist> | |
28 | <varlistentry> | |
29 | <term><parameter>fd</parameter></term> | |
30 | <listitem> | |
31 | <para>&fd;</para> | |
32 | </listitem> | |
33 | </varlistentry> | |
34 | <varlistentry> | |
35 | <term><parameter>request</parameter></term> | |
36 | <listitem> | |
37 | <para>VIDIOC_G_PARM, VIDIOC_S_PARM</para> | |
38 | </listitem> | |
39 | </varlistentry> | |
40 | <varlistentry> | |
41 | <term><parameter>argp</parameter></term> | |
42 | <listitem> | |
43 | <para></para> | |
44 | </listitem> | |
45 | </varlistentry> | |
46 | </variablelist> | |
47 | </refsect1> | |
48 | ||
49 | <refsect1> | |
50 | <title>Description</title> | |
51 | ||
52 | <para>The current video standard determines a nominal number of | |
53 | frames per second. If less than this number of frames is to be | |
54 | captured or output, applications can request frame skipping or | |
55 | duplicating on the driver side. This is especially useful when using | |
56 | the <function>read()</function> or <function>write()</function>, which | |
57 | are not augmented by timestamps or sequence counters, and to avoid | |
3ad2f3fb | 58 | unnecessary data copying.</para> |
8e080c2e MCC |
59 | |
60 | <para>Further these ioctls can be used to determine the number of | |
61 | buffers used internally by a driver in read/write mode. For | |
62 | implications see the section discussing the &func-read; | |
63 | function.</para> | |
64 | ||
65 | <para>To get and set the streaming parameters applications call | |
66 | the <constant>VIDIOC_G_PARM</constant> and | |
67 | <constant>VIDIOC_S_PARM</constant> ioctl, respectively. They take a | |
68 | pointer to a struct <structname>v4l2_streamparm</structname> which | |
69 | contains a union holding separate parameters for input and output | |
70 | devices.</para> | |
71 | ||
72 | <table pgwide="1" frame="none" id="v4l2-streamparm"> | |
73 | <title>struct <structname>v4l2_streamparm</structname></title> | |
74 | <tgroup cols="4"> | |
75 | &cs-ustr; | |
76 | <tbody valign="top"> | |
77 | <row> | |
78 | <entry>&v4l2-buf-type;</entry> | |
79 | <entry><structfield>type</structfield></entry> | |
80 | <entry></entry> | |
81 | <entry>The buffer (stream) type, same as &v4l2-format; | |
82 | <structfield>type</structfield>, set by the application.</entry> | |
83 | </row> | |
84 | <row> | |
85 | <entry>union</entry> | |
86 | <entry><structfield>parm</structfield></entry> | |
87 | <entry></entry> | |
88 | <entry></entry> | |
89 | </row> | |
90 | <row> | |
91 | <entry></entry> | |
92 | <entry>&v4l2-captureparm;</entry> | |
93 | <entry><structfield>capture</structfield></entry> | |
94 | <entry>Parameters for capture devices, used when | |
95 | <structfield>type</structfield> is | |
96 | <constant>V4L2_BUF_TYPE_VIDEO_CAPTURE</constant>.</entry> | |
97 | </row> | |
98 | <row> | |
99 | <entry></entry> | |
100 | <entry>&v4l2-outputparm;</entry> | |
101 | <entry><structfield>output</structfield></entry> | |
102 | <entry>Parameters for output devices, used when | |
103 | <structfield>type</structfield> is | |
104 | <constant>V4L2_BUF_TYPE_VIDEO_OUTPUT</constant>.</entry> | |
105 | </row> | |
106 | <row> | |
107 | <entry></entry> | |
108 | <entry>__u8</entry> | |
109 | <entry><structfield>raw_data</structfield>[200]</entry> | |
110 | <entry>A place holder for future extensions and custom | |
111 | (driver defined) buffer types <constant>V4L2_BUF_TYPE_PRIVATE</constant> and | |
112 | higher.</entry> | |
113 | </row> | |
114 | </tbody> | |
115 | </tgroup> | |
116 | </table> | |
117 | ||
118 | <table pgwide="1" frame="none" id="v4l2-captureparm"> | |
119 | <title>struct <structname>v4l2_captureparm</structname></title> | |
120 | <tgroup cols="3"> | |
121 | &cs-str; | |
122 | <tbody valign="top"> | |
123 | <row> | |
124 | <entry>__u32</entry> | |
125 | <entry><structfield>capability</structfield></entry> | |
126 | <entry>See <xref linkend="parm-caps" />.</entry> | |
127 | </row> | |
128 | <row> | |
129 | <entry>__u32</entry> | |
130 | <entry><structfield>capturemode</structfield></entry> | |
131 | <entry>Set by drivers and applications, see <xref linkend="parm-flags" />.</entry> | |
132 | </row> | |
133 | <row> | |
134 | <entry>&v4l2-fract;</entry> | |
135 | <entry><structfield>timeperframe</structfield></entry> | |
136 | <entry><para>This is is the desired period between | |
137 | successive frames captured by the driver, in seconds. The | |
138 | field is intended to skip frames on the driver side, saving I/O | |
139 | bandwidth.</para><para>Applications store here the desired frame | |
140 | period, drivers return the actual frame period, which must be greater | |
141 | or equal to the nominal frame period determined by the current video | |
142 | standard (&v4l2-standard; <structfield>frameperiod</structfield> | |
143 | field). Changing the video standard (also implicitly by switching the | |
144 | video input) may reset this parameter to the nominal frame period. To | |
145 | reset manually applications can just set this field to | |
146 | zero.</para><para>Drivers support this function only when they set the | |
147 | <constant>V4L2_CAP_TIMEPERFRAME</constant> flag in the | |
148 | <structfield>capability</structfield> field.</para></entry> | |
149 | </row> | |
150 | <row> | |
151 | <entry>__u32</entry> | |
152 | <entry><structfield>extendedmode</structfield></entry> | |
153 | <entry>Custom (driver specific) streaming parameters. When | |
154 | unused, applications and drivers must set this field to zero. | |
155 | Applications using this field should check the driver name and | |
156 | version, see <xref linkend="querycap" />.</entry> | |
157 | </row> | |
158 | <row> | |
159 | <entry>__u32</entry> | |
160 | <entry><structfield>readbuffers</structfield></entry> | |
161 | <entry>Applications set this field to the desired number | |
162 | of buffers used internally by the driver in &func-read; mode. Drivers | |
163 | return the actual number of buffers. When an application requests zero | |
164 | buffers, drivers should just return the current setting rather than | |
165 | the minimum or an error code. For details see <xref | |
166 | linkend="rw" />.</entry> | |
167 | </row> | |
168 | <row> | |
169 | <entry>__u32</entry> | |
170 | <entry><structfield>reserved</structfield>[4]</entry> | |
171 | <entry>Reserved for future extensions. Drivers and | |
172 | applications must set the array to zero.</entry> | |
173 | </row> | |
174 | </tbody> | |
175 | </tgroup> | |
176 | </table> | |
177 | ||
178 | <table pgwide="1" frame="none" id="v4l2-outputparm"> | |
179 | <title>struct <structname>v4l2_outputparm</structname></title> | |
180 | <tgroup cols="3"> | |
181 | &cs-str; | |
182 | <tbody valign="top"> | |
183 | <row> | |
184 | <entry>__u32</entry> | |
185 | <entry><structfield>capability</structfield></entry> | |
186 | <entry>See <xref linkend="parm-caps" />.</entry> | |
187 | </row> | |
188 | <row> | |
189 | <entry>__u32</entry> | |
190 | <entry><structfield>outputmode</structfield></entry> | |
191 | <entry>Set by drivers and applications, see <xref | |
192 | linkend="parm-flags" />.</entry> | |
193 | </row> | |
194 | <row> | |
195 | <entry>&v4l2-fract;</entry> | |
196 | <entry><structfield>timeperframe</structfield></entry> | |
197 | <entry>This is is the desired period between | |
198 | successive frames output by the driver, in seconds.</entry> | |
199 | </row> | |
200 | <row> | |
201 | <entry spanname="hspan"><para>The field is intended to | |
202 | repeat frames on the driver side in &func-write; mode (in streaming | |
203 | mode timestamps can be used to throttle the output), saving I/O | |
204 | bandwidth.</para><para>Applications store here the desired frame | |
205 | period, drivers return the actual frame period, which must be greater | |
206 | or equal to the nominal frame period determined by the current video | |
207 | standard (&v4l2-standard; <structfield>frameperiod</structfield> | |
208 | field). Changing the video standard (also implicitly by switching the | |
209 | video output) may reset this parameter to the nominal frame period. To | |
210 | reset manually applications can just set this field to | |
211 | zero.</para><para>Drivers support this function only when they set the | |
212 | <constant>V4L2_CAP_TIMEPERFRAME</constant> flag in the | |
213 | <structfield>capability</structfield> field.</para></entry> | |
214 | </row> | |
215 | <row> | |
216 | <entry>__u32</entry> | |
217 | <entry><structfield>extendedmode</structfield></entry> | |
218 | <entry>Custom (driver specific) streaming parameters. When | |
219 | unused, applications and drivers must set this field to zero. | |
220 | Applications using this field should check the driver name and | |
221 | version, see <xref linkend="querycap" />.</entry> | |
222 | </row> | |
223 | <row> | |
224 | <entry>__u32</entry> | |
225 | <entry><structfield>writebuffers</structfield></entry> | |
226 | <entry>Applications set this field to the desired number | |
227 | of buffers used internally by the driver in | |
228 | <function>write()</function> mode. Drivers return the actual number of | |
229 | buffers. When an application requests zero buffers, drivers should | |
230 | just return the current setting rather than the minimum or an error | |
231 | code. For details see <xref linkend="rw" />.</entry> | |
232 | </row> | |
233 | <row> | |
234 | <entry>__u32</entry> | |
235 | <entry><structfield>reserved</structfield>[4]</entry> | |
236 | <entry>Reserved for future extensions. Drivers and | |
237 | applications must set the array to zero.</entry> | |
238 | </row> | |
239 | </tbody> | |
240 | </tgroup> | |
241 | </table> | |
242 | ||
243 | <table pgwide="1" frame="none" id="parm-caps"> | |
244 | <title>Streaming Parameters Capabilites</title> | |
245 | <tgroup cols="3"> | |
246 | &cs-def; | |
247 | <tbody valign="top"> | |
248 | <row> | |
249 | <entry><constant>V4L2_CAP_TIMEPERFRAME</constant></entry> | |
250 | <entry>0x1000</entry> | |
251 | <entry>The frame skipping/repeating controlled by the | |
252 | <structfield>timeperframe</structfield> field is supported.</entry> | |
253 | </row> | |
254 | </tbody> | |
255 | </tgroup> | |
256 | </table> | |
257 | ||
258 | <table pgwide="1" frame="none" id="parm-flags"> | |
259 | <title>Capture Parameters Flags</title> | |
260 | <tgroup cols="3"> | |
261 | &cs-def; | |
262 | <tbody valign="top"> | |
263 | <row> | |
264 | <entry><constant>V4L2_MODE_HIGHQUALITY</constant></entry> | |
265 | <entry>0x0001</entry> | |
266 | <entry><para>High quality imaging mode. High quality mode | |
267 | is intended for still imaging applications. The idea is to get the | |
268 | best possible image quality that the hardware can deliver. It is not | |
269 | defined how the driver writer may achieve that; it will depend on the | |
270 | hardware and the ingenuity of the driver writer. High quality mode is | |
271 | a different mode from the the regular motion video capture modes. In | |
272 | high quality mode:<itemizedlist> | |
273 | <listitem> | |
274 | <para>The driver may be able to capture higher | |
275 | resolutions than for motion capture.</para> | |
276 | </listitem> | |
277 | <listitem> | |
278 | <para>The driver may support fewer pixel formats | |
279 | than motion capture (eg; true color).</para> | |
280 | </listitem> | |
281 | <listitem> | |
282 | <para>The driver may capture and arithmetically | |
283 | combine multiple successive fields or frames to remove color edge | |
284 | artifacts and reduce the noise in the video data. | |
285 | </para> | |
286 | </listitem> | |
287 | <listitem> | |
288 | <para>The driver may capture images in slices like | |
289 | a scanner in order to handle larger format images than would otherwise | |
290 | be possible. </para> | |
291 | </listitem> | |
292 | <listitem> | |
293 | <para>An image capture operation may be | |
294 | significantly slower than motion capture. </para> | |
295 | </listitem> | |
296 | <listitem> | |
297 | <para>Moving objects in the image might have | |
298 | excessive motion blur. </para> | |
299 | </listitem> | |
300 | <listitem> | |
301 | <para>Capture might only work through the | |
302 | <function>read()</function> call.</para> | |
303 | </listitem> | |
304 | </itemizedlist></para></entry> | |
305 | </row> | |
306 | </tbody> | |
307 | </tgroup> | |
308 | </table> | |
309 | ||
310 | </refsect1> | |
311 | ||
312 | <refsect1> | |
313 | &return-value; | |
314 | ||
315 | <variablelist> | |
316 | <varlistentry> | |
317 | <term><errorcode>EINVAL</errorcode></term> | |
318 | <listitem> | |
319 | <para>This ioctl is not supported.</para> | |
320 | </listitem> | |
321 | </varlistentry> | |
322 | </variablelist> | |
323 | </refsect1> | |
324 | </refentry> | |
325 | ||
326 | <!-- | |
327 | Local Variables: | |
328 | mode: sgml | |
329 | sgml-parent-document: "v4l2.sgml" | |
330 | indent-tabs-mode: nil | |
331 | End: | |
332 | --> |