1<refentry id="vidioc-g-enc-index">
2  <refmeta>
3    <refentrytitle>ioctl VIDIOC_G_ENC_INDEX</refentrytitle>
4    &manvol;
5  </refmeta>
6
7  <refnamediv>
8    <refname>VIDIOC_G_ENC_INDEX</refname>
9    <refpurpose>Get meta data about a compressed video stream</refpurpose>
10  </refnamediv>
11
12  <refsynopsisdiv>
13    <funcsynopsis>
14      <funcprototype>
15	<funcdef>int <function>ioctl</function></funcdef>
16	<paramdef>int <parameter>fd</parameter></paramdef>
17	<paramdef>int <parameter>request</parameter></paramdef>
18	<paramdef>struct v4l2_enc_idx *<parameter>argp</parameter></paramdef>
19      </funcprototype>
20    </funcsynopsis>
21  </refsynopsisdiv>
22
23  <refsect1>
24    <title>Arguments</title>
25
26    <variablelist>
27      <varlistentry>
28	<term><parameter>fd</parameter></term>
29	<listitem>
30	  <para>&fd;</para>
31	</listitem>
32      </varlistentry>
33      <varlistentry>
34	<term><parameter>request</parameter></term>
35	<listitem>
36	  <para>VIDIOC_G_ENC_INDEX</para>
37	</listitem>
38      </varlistentry>
39      <varlistentry>
40	<term><parameter>argp</parameter></term>
41	<listitem>
42	  <para></para>
43	</listitem>
44      </varlistentry>
45    </variablelist>
46  </refsect1>
47
48  <refsect1>
49    <title>Description</title>
50
51    <para>The <constant>VIDIOC_G_ENC_INDEX</constant> ioctl provides
52meta data about a compressed video stream the same or another
53application currently reads from the driver, which is useful for
54random access into the stream without decoding it.</para>
55
56    <para>To read the data applications must call
57<constant>VIDIOC_G_ENC_INDEX</constant> with a pointer to a
58&v4l2-enc-idx;. On success the driver fills the
59<structfield>entry</structfield> array, stores the number of elements
60written in the <structfield>entries</structfield> field, and
61initializes the <structfield>entries_cap</structfield> field.</para>
62
63    <para>Each element of the <structfield>entry</structfield> array
64contains meta data about one picture. A
65<constant>VIDIOC_G_ENC_INDEX</constant> call reads up to
66<constant>V4L2_ENC_IDX_ENTRIES</constant> entries from a driver
67buffer, which can hold up to <structfield>entries_cap</structfield>
68entries. This number can be lower or higher than
69<constant>V4L2_ENC_IDX_ENTRIES</constant>, but not zero. When the
70application fails to read the meta data in time the oldest entries
71will be lost. When the buffer is empty or no capturing/encoding is in
72progress, <structfield>entries</structfield> will be zero.</para>
73
74    <para>Currently this ioctl is only defined for MPEG-2 program
75streams and video elementary streams.</para>
76
77    <table pgwide="1" frame="none" id="v4l2-enc-idx">
78      <title>struct <structname>v4l2_enc_idx</structname></title>
79      <tgroup cols="3">
80	&cs-str;
81	<tbody valign="top">
82	  <row>
83	    <entry>__u32</entry>
84	    <entry><structfield>entries</structfield></entry>
85	    <entry>The number of entries the driver stored in the
86<structfield>entry</structfield> array.</entry>
87	  </row>
88	  <row>
89	    <entry>__u32</entry>
90	    <entry><structfield>entries_cap</structfield></entry>
91	    <entry>The number of entries the driver can
92buffer. Must be greater than zero.</entry>
93	  </row>
94	  <row>
95	    <entry>__u32</entry>
96	    <entry><structfield>reserved</structfield>[4]</entry>
97	    <entry spanname="hspan">Reserved for future extensions.
98Drivers must set the array to zero.</entry>
99	  </row>
100	  <row>
101	    <entry>&v4l2-enc-idx-entry;</entry>
102	    <entry><structfield>entry</structfield>[<constant>V4L2_ENC_IDX_ENTRIES</constant>]</entry>
103	    <entry>Meta data about a compressed video stream. Each
104element of the array corresponds to one picture, sorted in ascending
105order by their <structfield>offset</structfield>.</entry>
106	  </row>
107	</tbody>
108      </tgroup>
109    </table>
110
111    <table pgwide="1" frame="none" id="v4l2-enc-idx-entry">
112      <title>struct <structname>v4l2_enc_idx_entry</structname></title>
113      <tgroup cols="3">
114	&cs-str;
115	<tbody valign="top">
116	  <row>
117	    <entry>__u64</entry>
118	    <entry><structfield>offset</structfield></entry>
119	    <entry>The offset in bytes from the beginning of the
120compressed video stream to the beginning of this picture, that is a
121<wordasword>PES packet header</wordasword> as defined in <xref
122	    linkend="mpeg2part1" /> or a <wordasword>picture
123header</wordasword> as defined in <xref linkend="mpeg2part2" />. When
124the encoder is stopped, the driver resets the offset to zero.</entry>
125	  </row>
126	  <row>
127	    <entry>__u64</entry>
128	    <entry><structfield>pts</structfield></entry>
129	    <entry>The 33 bit <wordasword>Presentation Time
130Stamp</wordasword> of this picture as defined in <xref
131		linkend="mpeg2part1" />.</entry>
132	  </row>
133	  <row>
134	    <entry>__u32</entry>
135	    <entry><structfield>length</structfield></entry>
136	    <entry>The length of this picture in bytes.</entry>
137	  </row>
138	  <row>
139	    <entry>__u32</entry>
140	    <entry><structfield>flags</structfield></entry>
141	    <entry>Flags containing the coding type of this picture, see <xref
142		linkend="enc-idx-flags" />.</entry>
143	  </row>
144	  <row>
145	    <entry>__u32</entry>
146	    <entry><structfield>reserved</structfield>[2]</entry>
147	    <entry>Reserved for future extensions.
148Drivers must set the array to zero.</entry>
149	  </row>
150	</tbody>
151      </tgroup>
152    </table>
153
154    <table pgwide="1" frame="none" id="enc-idx-flags">
155      <title>Index Entry Flags</title>
156      <tgroup cols="3">
157	&cs-def;
158	<tbody valign="top">
159	  <row>
160	    <entry><constant>V4L2_ENC_IDX_FRAME_I</constant></entry>
161	    <entry>0x00</entry>
162	    <entry>This is an Intra-coded picture.</entry>
163	  </row>
164	  <row>
165	    <entry><constant>V4L2_ENC_IDX_FRAME_P</constant></entry>
166	    <entry>0x01</entry>
167	    <entry>This is a Predictive-coded picture.</entry>
168	  </row>
169	  <row>
170	    <entry><constant>V4L2_ENC_IDX_FRAME_B</constant></entry>
171	    <entry>0x02</entry>
172	    <entry>This is a Bidirectionally predictive-coded
173picture.</entry>
174	  </row>
175	  <row>
176	    <entry><constant>V4L2_ENC_IDX_FRAME_MASK</constant></entry>
177	    <entry>0x0F</entry>
178	    <entry><wordasword>AND</wordasword> the flags field with
179this mask to obtain the picture coding type.</entry>
180	  </row>
181       </tbody>
182      </tgroup>
183    </table>
184  </refsect1>
185
186  <refsect1>
187    &return-value;
188  </refsect1>
189</refentry>
190