Documentation/DocBook/v4l/vidioc-enum-frameintervals.xml

   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
 258     <para>See the description section above for a list of return
 259 values that <varname>errno</varname> can have.</para>
 260   </refsect1>
 261
 262 </refentry>
 263
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