Based on kernel version 4.7.2. Page generated on 2016-08-22 22:45 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. Must be zeroed by drivers and 221 applications.</entry> 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; 258 </refsect1> 259 260 </refentry>
