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Based on kernel version 3.13. Page generated on 2014-01-20 22:02 EST.

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>
220		    <entry>Reserved space for future use.</entry>
221		  </row>
222		</tbody>
223	      </tgroup>
224	    </table>
225	  </refsect1>
226	
227	  <refsect1>
228	    <title>Enums</title>
229	
230	    <table pgwide="1" frame="none" id="v4l2-frmivaltypes">
231	      <title>enum <structname>v4l2_frmivaltypes</structname></title>
232	      <tgroup cols="3">
233		&cs-def;
234		<tbody valign="top">
235		  <row>
236		    <entry><constant>V4L2_FRMIVAL_TYPE_DISCRETE</constant></entry>
237		    <entry>1</entry>
238		    <entry>Discrete frame interval.</entry>
239		  </row>
240		  <row>
241		    <entry><constant>V4L2_FRMIVAL_TYPE_CONTINUOUS</constant></entry>
242		    <entry>2</entry>
243		    <entry>Continuous frame interval.</entry>
244		  </row>
245		  <row>
246		    <entry><constant>V4L2_FRMIVAL_TYPE_STEPWISE</constant></entry>
247		    <entry>3</entry>
248		    <entry>Step-wise defined frame interval.</entry>
249		  </row>
250		</tbody>
251	      </tgroup>
252	    </table>
253	  </refsect1>
254	
255	  <refsect1>
256	    &return-value;
257	  </refsect1>
258	
259	</refentry>
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