]> git.kernelconcepts.de Git - karo-tx-linux.git/blob - Documentation/DocBook/media/v4l/vidioc-g-enc-index.xml
Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/cooloney...
[karo-tx-linux.git] / Documentation / DocBook / media / v4l / vidioc-g-enc-index.xml
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
52 meta data about a compressed video stream the same or another
53 application currently reads from the driver, which is useful for
54 random 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
60 written in the <structfield>entries</structfield> field, and
61 initializes the <structfield>entries_cap</structfield> field.</para>
62
63     <para>Each element of the <structfield>entry</structfield> array
64 contains 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
67 buffer, which can hold up to <structfield>entries_cap</structfield>
68 entries. This number can be lower or higher than
69 <constant>V4L2_ENC_IDX_ENTRIES</constant>, but not zero. When the
70 application fails to read the meta data in time the oldest entries
71 will be lost. When the buffer is empty or no capturing/encoding is in
72 progress, <structfield>entries</structfield> will be zero.</para>
73
74     <para>Currently this ioctl is only defined for MPEG-2 program
75 streams 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
92 buffer. 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.
98 Drivers 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
104 element of the array corresponds to one picture, sorted in ascending
105 order 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
120 compressed 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
123 header</wordasword> as defined in <xref linkend="mpeg2part2" />. When
124 the 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
130 Stamp</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.
148 Drivers 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
173 picture.</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
179 this 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>