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 44contains 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 54intervals that the device supports for the given pixel format and 55frame size.</para> 56 <para>The supported pixel formats and frame sizes can be obtained 57by using the &VIDIOC-ENUM-FMT; and &VIDIOC-ENUM-FRAMESIZES; 58functions.</para> 59 <para>The return value and the content of the 60<structfield>v4l2_frmivalenum.type</structfield> field depend on the 61type of frame intervals the device supports. Here are the semantics of 62the function for the different cases:</para> 63 <itemizedlist> 64 <listitem> 65 <para><emphasis role="bold">Discrete:</emphasis> The function 66returns success if the given index value (zero-based) is valid. The 67application should increase the index by one for each call until 68<constant>EINVAL</constant> is returned. The `v4l2_frmivalenum.type` 69field is set to `V4L2_FRMIVAL_TYPE_DISCRETE` by the driver. Of the 70union only the `discrete` member is valid.</para> 71 </listitem> 72 <listitem> 73 <para><emphasis role="bold">Step-wise:</emphasis> The function 74returns 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 78union only the <structfield>stepwise</structfield> member is 79valid.</para> 80 </listitem> 81 <listitem> 82 <para><emphasis role="bold">Continuous:</emphasis> This is a 83special case of the step-wise type above. The function returns success 84if the given index value is zero and <constant>EINVAL</constant> for 85any 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 88the union only the <structfield>stepwise</structfield> member is valid 89and 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 94must check the <structfield>type</structfield> field to determine the 95type of frame interval enumeration the device supports. Only for the 96<constant>V4L2_FRMIVAL_TYPE_DISCRETE</constant> type does it make 97sense to increase the index value to receive more frame 98intervals.</para> 99 <para>Note that the order in which the frame intervals are 100returned has no special meaning. In particular does it not say 101anything about potential default frame intervals.</para> 102 <para>Applications can assume that the enumeration data does not 103change without any interaction from the application itself. This means 104that the enumeration data is consistent if the application does not 105perform any other ioctl calls while it runs the frame interval 106enumeration.</para> 107 </refsect1> 108 109 <refsect1> 110 <title>Notes</title> 111 112 <itemizedlist> 113 <listitem> 114 <para><emphasis role="bold">Frame intervals and frame 115rates:</emphasis> The V4L2 API uses frame intervals instead of frame 116rates. Given the frame interval the frame rate can be computed as 117follows:<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 127value that has to be filled in by the application, 128<emphasis>OUT</emphasis> denotes values that the driver fills in. The 129application 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 169enumeration.</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 176enumerated.</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 183enumerated.</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 190enumerated.</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; 257 258 <para>See the description section above for a list of return 259values that <varname>errno</varname> can have.</para> 260 </refsect1> 261 262</refentry> 263 264<!-- 265Local Variables: 266mode: sgml 267sgml-parent-document: "v4l2.sgml" 268indent-tabs-mode: nil 269End: 270--> 271