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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 <note>
52 <title>Experimental</title>
53
54 <para>This is an <link linkend="experimental">experimental</link>
55interface and may change in the future.</para>
56 </note>
57
58 <para>The <constant>VIDIOC_G_ENC_INDEX</constant> ioctl provides
59meta data about a compressed video stream the same or another
60application currently reads from the driver, which is useful for
61random access into the stream without decoding it.</para>
62
63 <para>To read the data applications must call
64<constant>VIDIOC_G_ENC_INDEX</constant> with a pointer to a
65&v4l2-enc-idx;. On success the driver fills the
66<structfield>entry</structfield> array, stores the number of elements
67written in the <structfield>entries</structfield> field, and
68initializes the <structfield>entries_cap</structfield> field.</para>
69
70 <para>Each element of the <structfield>entry</structfield> array
71contains meta data about one picture. A
72<constant>VIDIOC_G_ENC_INDEX</constant> call reads up to
73<constant>V4L2_ENC_IDX_ENTRIES</constant> entries from a driver
74buffer, which can hold up to <structfield>entries_cap</structfield>
75entries. This number can be lower or higher than
76<constant>V4L2_ENC_IDX_ENTRIES</constant>, but not zero. When the
77application fails to read the meta data in time the oldest entries
78will be lost. When the buffer is empty or no capturing/encoding is in
79progress, <structfield>entries</structfield> will be zero.</para>
80
81 <para>Currently this ioctl is only defined for MPEG-2 program
82streams and video elementary streams.</para>
83
84 <table pgwide="1" frame="none" id="v4l2-enc-idx">
85 <title>struct <structname>v4l2_enc_idx</structname></title>
86 <tgroup cols="3">
87 &cs-str;
88 <tbody valign="top">
89 <row>
90 <entry>__u32</entry>
91 <entry><structfield>entries</structfield></entry>
92 <entry>The number of entries the driver stored in the
93<structfield>entry</structfield> array.</entry>
94 </row>
95 <row>
96 <entry>__u32</entry>
97 <entry><structfield>entries_cap</structfield></entry>
98 <entry>The number of entries the driver can
99buffer. Must be greater than zero.</entry>
100 </row>
101 <row>
102 <entry>__u32</entry>
103 <entry><structfield>reserved</structfield>[4]</entry>
104 <entry spanname="hspan">Reserved for future extensions.
105Drivers must set the array to zero.</entry>
106 </row>
107 <row>
108 <entry>&v4l2-enc-idx-entry;</entry>
109 <entry><structfield>entry</structfield>[<constant>V4L2_ENC_IDX_ENTRIES</constant>]</entry>
110 <entry>Meta data about a compressed video stream. Each
111element of the array corresponds to one picture, sorted in ascending
112order by their <structfield>offset</structfield>.</entry>
113 </row>
114 </tbody>
115 </tgroup>
116 </table>
117
118 <table pgwide="1" frame="none" id="v4l2-enc-idx-entry">
119 <title>struct <structname>v4l2_enc_idx_entry</structname></title>
120 <tgroup cols="3">
121 &cs-str;
122 <tbody valign="top">
123 <row>
124 <entry>__u64</entry>
125 <entry><structfield>offset</structfield></entry>
126 <entry>The offset in bytes from the beginning of the
127compressed video stream to the beginning of this picture, that is a
128<wordasword>PES packet header</wordasword> as defined in <xref
129 linkend="mpeg2part1" /> or a <wordasword>picture
130header</wordasword> as defined in <xref linkend="mpeg2part2" />. When
131the encoder is stopped, the driver resets the offset to zero.</entry>
132 </row>
133 <row>
134 <entry>__u64</entry>
135 <entry><structfield>pts</structfield></entry>
136 <entry>The 33 bit <wordasword>Presentation Time
137Stamp</wordasword> of this picture as defined in <xref
138 linkend="mpeg2part1" />.</entry>
139 </row>
140 <row>
141 <entry>__u32</entry>
142 <entry><structfield>length</structfield></entry>
143 <entry>The length of this picture in bytes.</entry>
144 </row>
145 <row>
146 <entry>__u32</entry>
147 <entry><structfield>flags</structfield></entry>
148 <entry>Flags containing the coding type of this picture, see <xref
149 linkend="enc-idx-flags" />.</entry>
150 </row>
151 <row>
152 <entry>__u32</entry>
153 <entry><structfield>reserved</structfield>[2]</entry>
154 <entry>Reserved for future extensions.
155Drivers must set the array to zero.</entry>
156 </row>
157 </tbody>
158 </tgroup>
159 </table>
160
161 <table pgwide="1" frame="none" id="enc-idx-flags">
162 <title>Index Entry Flags</title>
163 <tgroup cols="3">
164 &cs-def;
165 <tbody valign="top">
166 <row>
167 <entry><constant>V4L2_ENC_IDX_FRAME_I</constant></entry>
168 <entry>0x00</entry>
169 <entry>This is an Intra-coded picture.</entry>
170 </row>
171 <row>
172 <entry><constant>V4L2_ENC_IDX_FRAME_P</constant></entry>
173 <entry>0x01</entry>
174 <entry>This is a Predictive-coded picture.</entry>
175 </row>
176 <row>
177 <entry><constant>V4L2_ENC_IDX_FRAME_B</constant></entry>
178 <entry>0x02</entry>
179 <entry>This is a Bidirectionally predictive-coded
180picture.</entry>
181 </row>
182 <row>
183 <entry><constant>V4L2_ENC_IDX_FRAME_MASK</constant></entry>
184 <entry>0x0F</entry>
185 <entry><wordasword>AND</wordasword> the flags field with
186this mask to obtain the picture coding type.</entry>
187 </row>
188 </tbody>
189 </tgroup>
190 </table>
191 </refsect1>
192
193 <refsect1>
194 &return-value;
195
196 <variablelist>
197 <varlistentry>
198 <term><errorcode>EINVAL</errorcode></term>
199 <listitem>
200 <para>The driver does not support this ioctl.</para>
201 </listitem>
202 </varlistentry>
203 </variablelist>
204 </refsect1>
205</refentry>
206
207<!--
208Local Variables:
209mode: sgml
210sgml-parent-document: "v4l2.sgml"
211indent-tabs-mode: nil
212End:
213-->