Documentation/DocBook/media/v4l/vidioc-g-jpegcomp.xml

   1 <refentry id="vidioc-g-jpegcomp">
   2   <refmeta>
   3     <refentrytitle>ioctl VIDIOC_G_JPEGCOMP, VIDIOC_S_JPEGCOMP</refentrytitle>
   4     &manvol;
   5   </refmeta>
   6
   7   <refnamediv>
   8     <refname>VIDIOC_G_JPEGCOMP</refname>
   9     <refname>VIDIOC_S_JPEGCOMP</refname>
  10     <refpurpose></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>v4l2_jpegcompression *<parameter>argp</parameter></paramdef>
  20       </funcprototype>
  21     </funcsynopsis>
  22     <funcsynopsis>
  23       <funcprototype>
  24         <funcdef>int <function>ioctl</function></funcdef>
  25         <paramdef>int <parameter>fd</parameter></paramdef>
  26         <paramdef>int <parameter>request</parameter></paramdef>
  27         <paramdef>const v4l2_jpegcompression *<parameter>argp</parameter></paramdef>
  28       </funcprototype>
  29     </funcsynopsis>
  30   </refsynopsisdiv>
  31
  32   <refsect1>
  33     <title>Arguments</title>
  34
  35     <variablelist>
  36       <varlistentry>
  37         <term><parameter>fd</parameter></term>
  38         <listitem>
  39           <para>&fd;</para>
  40         </listitem>
  41       </varlistentry>
  42       <varlistentry>
  43         <term><parameter>request</parameter></term>
  44         <listitem>
  45           <para>VIDIOC_G_JPEGCOMP, VIDIOC_S_JPEGCOMP</para>
  46         </listitem>
  47       </varlistentry>
  48       <varlistentry>
  49         <term><parameter>argp</parameter></term>
  50         <listitem>
  51           <para></para>
  52         </listitem>
  53       </varlistentry>
  54     </variablelist>
  55   </refsect1>
  56
  57   <refsect1>
  58     <title>Description</title>
  59
  60     <para>[to do]</para>
  61
  62     <para>Ronald Bultje elaborates:</para>
  63
  64     <!-- See video4linux-list@redhat.com on 16 Oct 2002, subject
  65 "Re: [V4L] Re: v4l2 api / Zoran v4l2_jpegcompression" -->
  66
  67     <para>APP is some application-specific information. The
  68 application can set it itself, and it'll be stored in the JPEG-encoded
  69 fields (eg; interlacing information for in an AVI or so). COM is the
  70 same, but it's comments, like 'encoded by me' or so.</para>
  71
  72     <para>jpeg_markers describes whether the huffman tables,
  73 quantization tables and the restart interval information (all
  74 JPEG-specific stuff) should be stored in the JPEG-encoded fields.
  75 These define how the JPEG field is encoded. If you omit them,
  76 applications assume you've used standard encoding. You usually do want
  77 to add them.</para>
  78
  79     <!-- NB VIDIOC_S_JPEGCOMP is w/o. -->
  80
  81     <table pgwide="1" frame="none" id="v4l2-jpegcompression">
  82       <title>struct <structname>v4l2_jpegcompression</structname></title>
  83       <tgroup cols="3">
  84         &cs-str;
  85         <tbody valign="top">
  86           <row>
  87             <entry>int</entry>
  88             <entry><structfield>quality</structfield></entry>
  89             <entry></entry>
  90           </row>
  91           <row>
  92             <entry>int</entry>
  93             <entry><structfield>APPn</structfield></entry>
  94             <entry></entry>
  95           </row>
  96           <row>
  97             <entry>int</entry>
  98             <entry><structfield>APP_len</structfield></entry>
  99             <entry></entry>
 100           </row>
 101           <row>
 102             <entry>char</entry>
 103             <entry><structfield>APP_data</structfield>[60]</entry>
 104             <entry></entry>
 105           </row>
 106           <row>
 107             <entry>int</entry>
 108             <entry><structfield>COM_len</structfield></entry>
 109             <entry></entry>
 110           </row>
 111           <row>
 112             <entry>char</entry>
 113             <entry><structfield>COM_data</structfield>[60]</entry>
 114             <entry></entry>
 115           </row>
 116           <row>
 117             <entry>__u32</entry>
 118             <entry><structfield>jpeg_markers</structfield></entry>
 119             <entry>See <xref linkend="jpeg-markers" />.</entry>
 120           </row>
 121         </tbody>
 122       </tgroup>
 123     </table>
 124
 125     <table pgwide="1" frame="none" id="jpeg-markers">
 126       <title>JPEG Markers Flags</title>
 127       <tgroup cols="3">
 128         &cs-def;
 129         <tbody valign="top">
 130           <row>
 131             <entry><constant>V4L2_JPEG_MARKER_DHT</constant></entry>
 132             <entry>(1&lt;&lt;3)</entry>
 133             <entry>Define Huffman Tables</entry>
 134           </row>
 135           <row>
 136             <entry><constant>V4L2_JPEG_MARKER_DQT</constant></entry>
 137             <entry>(1&lt;&lt;4)</entry>
 138             <entry>Define Quantization Tables</entry>
 139           </row>
 140           <row>
 141             <entry><constant>V4L2_JPEG_MARKER_DRI</constant></entry>
 142             <entry>(1&lt;&lt;5)</entry>
 143             <entry>Define Restart Interval</entry>
 144           </row>
 145           <row>
 146             <entry><constant>V4L2_JPEG_MARKER_COM</constant></entry>
 147             <entry>(1&lt;&lt;6)</entry>
 148             <entry>Comment segment</entry>
 149           </row>
 150           <row>
 151             <entry><constant>V4L2_JPEG_MARKER_APP</constant></entry>
 152             <entry>(1&lt;&lt;7)</entry>
 153             <entry>App segment, driver will always use APP0</entry>
 154           </row>
 155         </tbody>
 156       </tgroup>
 157     </table>
 158   </refsect1>
 159
 160   <refsect1>
 161     &return-value;
 162   </refsect1>
 163 </refentry>