summaryrefslogtreecommitdiffstats
path: root/Documentation/DocBook/media/v4l/vidioc-g-enc-index.xml
blob: be25029a16f11dff77a39e5b026fe888db4f5ada (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
<refentry id="vidioc-g-enc-index">
  <refmeta>
    <refentrytitle>ioctl VIDIOC_G_ENC_INDEX</refentrytitle>
    &manvol;
  </refmeta>

  <refnamediv>
    <refname>VIDIOC_G_ENC_INDEX</refname>
    <refpurpose>Get meta data about a compressed video stream</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <funcsynopsis>
      <funcprototype>
	<funcdef>int <function>ioctl</function></funcdef>
	<paramdef>int <parameter>fd</parameter></paramdef>
	<paramdef>int <parameter>request</parameter></paramdef>
	<paramdef>struct v4l2_enc_idx *<parameter>argp</parameter></paramdef>
      </funcprototype>
    </funcsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Arguments</title>

    <variablelist>
      <varlistentry>
	<term><parameter>fd</parameter></term>
	<listitem>
	  <para>&fd;</para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term><parameter>request</parameter></term>
	<listitem>
	  <para>VIDIOC_G_ENC_INDEX</para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term><parameter>argp</parameter></term>
	<listitem>
	  <para></para>
	</listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1>
    <title>Description</title>

    <para>The <constant>VIDIOC_G_ENC_INDEX</constant> ioctl provides
meta data about a compressed video stream the same or another
application currently reads from the driver, which is useful for
random access into the stream without decoding it.</para>

    <para>To read the data applications must call
<constant>VIDIOC_G_ENC_INDEX</constant> with a pointer to a
&v4l2-enc-idx;. On success the driver fills the
<structfield>entry</structfield> array, stores the number of elements
written in the <structfield>entries</structfield> field, and
initializes the <structfield>entries_cap</structfield> field.</para>

    <para>Each element of the <structfield>entry</structfield> array
contains meta data about one picture. A
<constant>VIDIOC_G_ENC_INDEX</constant> call reads up to
<constant>V4L2_ENC_IDX_ENTRIES</constant> entries from a driver
buffer, which can hold up to <structfield>entries_cap</structfield>
entries. This number can be lower or higher than
<constant>V4L2_ENC_IDX_ENTRIES</constant>, but not zero. When the
application fails to read the meta data in time the oldest entries
will be lost. When the buffer is empty or no capturing/encoding is in
progress, <structfield>entries</structfield> will be zero.</para>

    <para>Currently this ioctl is only defined for MPEG-2 program
streams and video elementary streams.</para>

    <table pgwide="1" frame="none" id="v4l2-enc-idx">
      <title>struct <structname>v4l2_enc_idx</structname></title>
      <tgroup cols="3">
	&cs-str;
	<tbody valign="top">
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>entries</structfield></entry>
	    <entry>The number of entries the driver stored in the
<structfield>entry</structfield> array.</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>entries_cap</structfield></entry>
	    <entry>The number of entries the driver can
buffer. Must be greater than zero.</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>reserved</structfield>[4]</entry>
	    <entry spanname="hspan">Reserved for future extensions.
Drivers must set the array to zero.</entry>
	  </row>
	  <row>
	    <entry>&v4l2-enc-idx-entry;</entry>
	    <entry><structfield>entry</structfield>[<constant>V4L2_ENC_IDX_ENTRIES</constant>]</entry>
	    <entry>Meta data about a compressed video stream. Each
element of the array corresponds to one picture, sorted in ascending
order by their <structfield>offset</structfield>.</entry>
	  </row>
	</tbody>
      </tgroup>
    </table>

    <table pgwide="1" frame="none" id="v4l2-enc-idx-entry">
      <title>struct <structname>v4l2_enc_idx_entry</structname></title>
      <tgroup cols="3">
	&cs-str;
	<tbody valign="top">
	  <row>
	    <entry>__u64</entry>
	    <entry><structfield>offset</structfield></entry>
	    <entry>The offset in bytes from the beginning of the
compressed video stream to the beginning of this picture, that is a
<wordasword>PES packet header</wordasword> as defined in <xref
	    linkend="mpeg2part1" /> or a <wordasword>picture
header</wordasword> as defined in <xref linkend="mpeg2part2" />. When
the encoder is stopped, the driver resets the offset to zero.</entry>
	  </row>
	  <row>
	    <entry>__u64</entry>
	    <entry><structfield>pts</structfield></entry>
	    <entry>The 33 bit <wordasword>Presentation Time
Stamp</wordasword> of this picture as defined in <xref
		linkend="mpeg2part1" />.</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>length</structfield></entry>
	    <entry>The length of this picture in bytes.</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>flags</structfield></entry>
	    <entry>Flags containing the coding type of this picture, see <xref
		linkend="enc-idx-flags" />.</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>reserved</structfield>[2]</entry>
	    <entry>Reserved for future extensions.
Drivers must set the array to zero.</entry>
	  </row>
	</tbody>
      </tgroup>
    </table>

    <table pgwide="1" frame="none" id="enc-idx-flags">
      <title>Index Entry Flags</title>
      <tgroup cols="3">
	&cs-def;
	<tbody valign="top">
	  <row>
	    <entry><constant>V4L2_ENC_IDX_FRAME_I</constant></entry>
	    <entry>0x00</entry>
	    <entry>This is an Intra-coded picture.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_ENC_IDX_FRAME_P</constant></entry>
	    <entry>0x01</entry>
	    <entry>This is a Predictive-coded picture.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_ENC_IDX_FRAME_B</constant></entry>
	    <entry>0x02</entry>
	    <entry>This is a Bidirectionally predictive-coded
picture.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_ENC_IDX_FRAME_MASK</constant></entry>
	    <entry>0x0F</entry>
	    <entry><wordasword>AND</wordasword> the flags field with
this mask to obtain the picture coding type.</entry>
	  </row>
       </tbody>
      </tgroup>
    </table>
  </refsect1>

  <refsect1>
    &return-value;
  </refsect1>
</refentry>