Based on kernel version 3.0.4. Page generated on 2011-10-03 22:07 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 <note> 52 <title>Experimental</title> 53 54 <para>This is an <link linkend="experimental">experimental</link> 55 interface and may change in the future.</para> 56 </note> 57 58 <para>The <constant>VIDIOC_G_ENC_INDEX</constant> ioctl provides 59 meta data about a compressed video stream the same or another 60 application currently reads from the driver, which is useful for 61 random 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 67 written in the <structfield>entries</structfield> field, and 68 initializes the <structfield>entries_cap</structfield> field.</para> 69 70 <para>Each element of the <structfield>entry</structfield> array 71 contains 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 74 buffer, which can hold up to <structfield>entries_cap</structfield> 75 entries. This number can be lower or higher than 76 <constant>V4L2_ENC_IDX_ENTRIES</constant>, but not zero. When the 77 application fails to read the meta data in time the oldest entries 78 will be lost. When the buffer is empty or no capturing/encoding is in 79 progress, <structfield>entries</structfield> will be zero.</para> 80 81 <para>Currently this ioctl is only defined for MPEG-2 program 82 streams 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 99 buffer. 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. 105 Drivers 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 111 element of the array corresponds to one picture, sorted in ascending 112 order 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 127 compressed 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 130 header</wordasword> as defined in <xref linkend="mpeg2part2" />. When 131 the 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 137 Stamp</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. 155 Drivers 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 180 picture.</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 186 this 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 <!-- 208 Local Variables: 209 mode: sgml 210 sgml-parent-document: "v4l2.sgml" 211 indent-tabs-mode: nil 212 End: 213 -->
