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  </refsect1>
196</refentry>
197