Based on kernel version 4.7.2. Page generated on 2016-08-22 22:45 EST.
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>
