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1 | <refentry id="vidioc-enum-frameintervals"> |
2 | ||
3 | <refmeta> | |
4 | <refentrytitle>ioctl VIDIOC_ENUM_FRAMEINTERVALS</refentrytitle> | |
5 | &manvol; | |
6 | </refmeta> | |
7 | ||
8 | <refnamediv> | |
9 | <refname>VIDIOC_ENUM_FRAMEINTERVALS</refname> | |
10 | <refpurpose>Enumerate frame intervals</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>struct v4l2_frmivalenum *<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_ENUM_FRAMEINTERVALS</para> | |
38 | </listitem> | |
39 | </varlistentry> | |
40 | <varlistentry> | |
41 | <term><parameter>argp</parameter></term> | |
42 | <listitem> | |
43 | <para>Pointer to a &v4l2-frmivalenum; structure that | |
44 | contains a pixel format and size and receives a frame interval.</para> | |
45 | </listitem> | |
46 | </varlistentry> | |
47 | </variablelist> | |
48 | </refsect1> | |
49 | ||
50 | <refsect1> | |
51 | <title>Description</title> | |
52 | ||
53 | <para>This ioctl allows applications to enumerate all frame | |
54 | intervals that the device supports for the given pixel format and | |
55 | frame size.</para> | |
56 | <para>The supported pixel formats and frame sizes can be obtained | |
57 | by using the &VIDIOC-ENUM-FMT; and &VIDIOC-ENUM-FRAMESIZES; | |
58 | functions.</para> | |
59 | <para>The return value and the content of the | |
60 | <structfield>v4l2_frmivalenum.type</structfield> field depend on the | |
61 | type of frame intervals the device supports. Here are the semantics of | |
62 | the function for the different cases:</para> | |
63 | <itemizedlist> | |
64 | <listitem> | |
65 | <para><emphasis role="bold">Discrete:</emphasis> The function | |
66 | returns success if the given index value (zero-based) is valid. The | |
67 | application should increase the index by one for each call until | |
68 | <constant>EINVAL</constant> is returned. The `v4l2_frmivalenum.type` | |
69 | field is set to `V4L2_FRMIVAL_TYPE_DISCRETE` by the driver. Of the | |
70 | union only the `discrete` member is valid.</para> | |
71 | </listitem> | |
72 | <listitem> | |
73 | <para><emphasis role="bold">Step-wise:</emphasis> The function | |
74 | returns success if the given index value is zero and | |
75 | <constant>EINVAL</constant> for any other index value. The | |
76 | <structfield>v4l2_frmivalenum.type</structfield> field is set to | |
77 | <constant>V4L2_FRMIVAL_TYPE_STEPWISE</constant> by the driver. Of the | |
78 | union only the <structfield>stepwise</structfield> member is | |
79 | valid.</para> | |
80 | </listitem> | |
81 | <listitem> | |
82 | <para><emphasis role="bold">Continuous:</emphasis> This is a | |
83 | special case of the step-wise type above. The function returns success | |
84 | if the given index value is zero and <constant>EINVAL</constant> for | |
85 | any other index value. The | |
86 | <structfield>v4l2_frmivalenum.type</structfield> field is set to | |
87 | <constant>V4L2_FRMIVAL_TYPE_CONTINUOUS</constant> by the driver. Of | |
88 | the union only the <structfield>stepwise</structfield> member is valid | |
89 | and the <structfield>step</structfield> value is set to 1.</para> | |
90 | </listitem> | |
91 | </itemizedlist> | |
92 | ||
93 | <para>When the application calls the function with index zero, it | |
94 | must check the <structfield>type</structfield> field to determine the | |
95 | type of frame interval enumeration the device supports. Only for the | |
96 | <constant>V4L2_FRMIVAL_TYPE_DISCRETE</constant> type does it make | |
97 | sense to increase the index value to receive more frame | |
98 | intervals.</para> | |
99 | <para>Note that the order in which the frame intervals are | |
100 | returned has no special meaning. In particular does it not say | |
101 | anything about potential default frame intervals.</para> | |
102 | <para>Applications can assume that the enumeration data does not | |
103 | change without any interaction from the application itself. This means | |
104 | that the enumeration data is consistent if the application does not | |
105 | perform any other ioctl calls while it runs the frame interval | |
106 | enumeration.</para> | |
107 | </refsect1> | |
108 | ||
109 | <refsect1> | |
110 | <title>Notes</title> | |
111 | ||
112 | <itemizedlist> | |
113 | <listitem> | |
114 | <para><emphasis role="bold">Frame intervals and frame | |
115 | rates:</emphasis> The V4L2 API uses frame intervals instead of frame | |
116 | rates. Given the frame interval the frame rate can be computed as | |
117 | follows:<screen>frame_rate = 1 / frame_interval</screen></para> | |
118 | </listitem> | |
119 | </itemizedlist> | |
120 | ||
121 | </refsect1> | |
122 | ||
123 | <refsect1> | |
124 | <title>Structs</title> | |
125 | ||
126 | <para>In the structs below, <emphasis>IN</emphasis> denotes a | |
127 | value that has to be filled in by the application, | |
128 | <emphasis>OUT</emphasis> denotes values that the driver fills in. The | |
129 | application should zero out all members except for the | |
130 | <emphasis>IN</emphasis> fields.</para> | |
131 | ||
132 | <table pgwide="1" frame="none" id="v4l2-frmival-stepwise"> | |
133 | <title>struct <structname>v4l2_frmival_stepwise</structname></title> | |
134 | <tgroup cols="3"> | |
135 | &cs-str; | |
136 | <tbody valign="top"> | |
137 | <row> | |
138 | <entry>&v4l2-fract;</entry> | |
139 | <entry><structfield>min</structfield></entry> | |
140 | <entry>Minimum frame interval [s].</entry> | |
141 | </row> | |
142 | <row> | |
143 | <entry>&v4l2-fract;</entry> | |
144 | <entry><structfield>max</structfield></entry> | |
145 | <entry>Maximum frame interval [s].</entry> | |
146 | </row> | |
147 | <row> | |
148 | <entry>&v4l2-fract;</entry> | |
149 | <entry><structfield>step</structfield></entry> | |
150 | <entry>Frame interval step size [s].</entry> | |
151 | </row> | |
152 | </tbody> | |
153 | </tgroup> | |
154 | </table> | |
155 | ||
156 | <table pgwide="1" frame="none" id="v4l2-frmivalenum"> | |
157 | <title>struct <structname>v4l2_frmivalenum</structname></title> | |
158 | <tgroup cols="4"> | |
159 | <colspec colname="c1" /> | |
160 | <colspec colname="c2" /> | |
161 | <colspec colname="c3" /> | |
162 | <colspec colname="c4" /> | |
163 | <tbody valign="top"> | |
164 | <row> | |
165 | <entry>__u32</entry> | |
166 | <entry><structfield>index</structfield></entry> | |
167 | <entry></entry> | |
168 | <entry>IN: Index of the given frame interval in the | |
169 | enumeration.</entry> | |
170 | </row> | |
171 | <row> | |
172 | <entry>__u32</entry> | |
173 | <entry><structfield>pixel_format</structfield></entry> | |
174 | <entry></entry> | |
175 | <entry>IN: Pixel format for which the frame intervals are | |
176 | enumerated.</entry> | |
177 | </row> | |
178 | <row> | |
179 | <entry>__u32</entry> | |
180 | <entry><structfield>width</structfield></entry> | |
181 | <entry></entry> | |
182 | <entry>IN: Frame width for which the frame intervals are | |
183 | enumerated.</entry> | |
184 | </row> | |
185 | <row> | |
186 | <entry>__u32</entry> | |
187 | <entry><structfield>height</structfield></entry> | |
188 | <entry></entry> | |
189 | <entry>IN: Frame height for which the frame intervals are | |
190 | enumerated.</entry> | |
191 | </row> | |
192 | <row> | |
193 | <entry>__u32</entry> | |
194 | <entry><structfield>type</structfield></entry> | |
195 | <entry></entry> | |
196 | <entry>OUT: Frame interval type the device supports.</entry> | |
197 | </row> | |
198 | <row> | |
199 | <entry>union</entry> | |
200 | <entry></entry> | |
201 | <entry></entry> | |
202 | <entry>OUT: Frame interval with the given index.</entry> | |
203 | </row> | |
204 | <row> | |
205 | <entry></entry> | |
206 | <entry>&v4l2-fract;</entry> | |
207 | <entry><structfield>discrete</structfield></entry> | |
208 | <entry>Frame interval [s].</entry> | |
209 | </row> | |
210 | <row> | |
211 | <entry></entry> | |
212 | <entry>&v4l2-frmival-stepwise;</entry> | |
213 | <entry><structfield>stepwise</structfield></entry> | |
214 | <entry></entry> | |
215 | </row> | |
216 | <row> | |
217 | <entry>__u32</entry> | |
218 | <entry><structfield>reserved[2]</structfield></entry> | |
219 | <entry></entry> | |
dc8b1c0e HV |
220 | <entry>Reserved space for future use. Must be zeroed by drivers and |
221 | applications.</entry> | |
8e080c2e MCC |
222 | </row> |
223 | </tbody> | |
224 | </tgroup> | |
225 | </table> | |
226 | </refsect1> | |
227 | ||
228 | <refsect1> | |
229 | <title>Enums</title> | |
230 | ||
231 | <table pgwide="1" frame="none" id="v4l2-frmivaltypes"> | |
232 | <title>enum <structname>v4l2_frmivaltypes</structname></title> | |
233 | <tgroup cols="3"> | |
234 | &cs-def; | |
235 | <tbody valign="top"> | |
236 | <row> | |
237 | <entry><constant>V4L2_FRMIVAL_TYPE_DISCRETE</constant></entry> | |
238 | <entry>1</entry> | |
239 | <entry>Discrete frame interval.</entry> | |
240 | </row> | |
241 | <row> | |
242 | <entry><constant>V4L2_FRMIVAL_TYPE_CONTINUOUS</constant></entry> | |
243 | <entry>2</entry> | |
244 | <entry>Continuous frame interval.</entry> | |
245 | </row> | |
246 | <row> | |
247 | <entry><constant>V4L2_FRMIVAL_TYPE_STEPWISE</constant></entry> | |
248 | <entry>3</entry> | |
249 | <entry>Step-wise defined frame interval.</entry> | |
250 | </row> | |
251 | </tbody> | |
252 | </tgroup> | |
253 | </table> | |
254 | </refsect1> | |
255 | ||
256 | <refsect1> | |
257 | &return-value; | |
8e080c2e MCC |
258 | </refsect1> |
259 | ||
260 | </refentry> |