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
68application can set it itself, and it'll be stored in the JPEG-encoded
69fields (eg; interlacing information for in an AVI or so). COM is the
70same, but it's comments, like 'encoded by me' or so.</para>
71
72    <para>jpeg_markers describes whether the huffman tables,
73quantization tables and the restart interval information (all
74JPEG-specific stuff) should be stored in the JPEG-encoded fields.
75These define how the JPEG field is encoded. If you omit them,
76applications assume you've used standard encoding. You usually do want
77to 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>
164