mirror of https://gitee.com/openkylin/linux.git
190 lines
6.0 KiB
XML
190 lines
6.0 KiB
XML
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<refentry id="vidioc-g-enc-index">
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<refmeta>
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<refentrytitle>ioctl VIDIOC_G_ENC_INDEX</refentrytitle>
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&manvol;
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</refmeta>
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<refnamediv>
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<refname>VIDIOC_G_ENC_INDEX</refname>
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<refpurpose>Get meta data about a compressed video stream</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcprototype>
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<funcdef>int <function>ioctl</function></funcdef>
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<paramdef>int <parameter>fd</parameter></paramdef>
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<paramdef>int <parameter>request</parameter></paramdef>
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<paramdef>struct v4l2_enc_idx *<parameter>argp</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Arguments</title>
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<variablelist>
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<varlistentry>
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<term><parameter>fd</parameter></term>
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<listitem>
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<para>&fd;</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>request</parameter></term>
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<listitem>
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<para>VIDIOC_G_ENC_INDEX</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>argp</parameter></term>
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<listitem>
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<para></para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>Description</title>
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<para>The <constant>VIDIOC_G_ENC_INDEX</constant> ioctl provides
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meta data about a compressed video stream the same or another
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application currently reads from the driver, which is useful for
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random access into the stream without decoding it.</para>
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<para>To read the data applications must call
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<constant>VIDIOC_G_ENC_INDEX</constant> with a pointer to a
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&v4l2-enc-idx;. On success the driver fills the
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<structfield>entry</structfield> array, stores the number of elements
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written in the <structfield>entries</structfield> field, and
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initializes the <structfield>entries_cap</structfield> field.</para>
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<para>Each element of the <structfield>entry</structfield> array
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contains meta data about one picture. A
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<constant>VIDIOC_G_ENC_INDEX</constant> call reads up to
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<constant>V4L2_ENC_IDX_ENTRIES</constant> entries from a driver
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buffer, which can hold up to <structfield>entries_cap</structfield>
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entries. This number can be lower or higher than
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<constant>V4L2_ENC_IDX_ENTRIES</constant>, but not zero. When the
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application fails to read the meta data in time the oldest entries
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will be lost. When the buffer is empty or no capturing/encoding is in
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progress, <structfield>entries</structfield> will be zero.</para>
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<para>Currently this ioctl is only defined for MPEG-2 program
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streams and video elementary streams.</para>
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<table pgwide="1" frame="none" id="v4l2-enc-idx">
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<title>struct <structname>v4l2_enc_idx</structname></title>
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<tgroup cols="3">
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&cs-str;
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<tbody valign="top">
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<row>
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<entry>__u32</entry>
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<entry><structfield>entries</structfield></entry>
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<entry>The number of entries the driver stored in the
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<structfield>entry</structfield> array.</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>entries_cap</structfield></entry>
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<entry>The number of entries the driver can
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buffer. Must be greater than zero.</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>reserved</structfield>[4]</entry>
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<entry spanname="hspan">Reserved for future extensions.
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Drivers must set the array to zero.</entry>
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</row>
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<row>
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<entry>&v4l2-enc-idx-entry;</entry>
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<entry><structfield>entry</structfield>[<constant>V4L2_ENC_IDX_ENTRIES</constant>]</entry>
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<entry>Meta data about a compressed video stream. Each
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element of the array corresponds to one picture, sorted in ascending
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order by their <structfield>offset</structfield>.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<table pgwide="1" frame="none" id="v4l2-enc-idx-entry">
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<title>struct <structname>v4l2_enc_idx_entry</structname></title>
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<tgroup cols="3">
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&cs-str;
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<tbody valign="top">
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<row>
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<entry>__u64</entry>
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<entry><structfield>offset</structfield></entry>
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<entry>The offset in bytes from the beginning of the
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compressed video stream to the beginning of this picture, that is a
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<wordasword>PES packet header</wordasword> as defined in <xref
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linkend="mpeg2part1" /> or a <wordasword>picture
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header</wordasword> as defined in <xref linkend="mpeg2part2" />. When
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the encoder is stopped, the driver resets the offset to zero.</entry>
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</row>
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<row>
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<entry>__u64</entry>
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<entry><structfield>pts</structfield></entry>
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<entry>The 33 bit <wordasword>Presentation Time
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Stamp</wordasword> of this picture as defined in <xref
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linkend="mpeg2part1" />.</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>length</structfield></entry>
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<entry>The length of this picture in bytes.</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>flags</structfield></entry>
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<entry>Flags containing the coding type of this picture, see <xref
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linkend="enc-idx-flags" />.</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>reserved</structfield>[2]</entry>
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<entry>Reserved for future extensions.
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Drivers must set the array to zero.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<table pgwide="1" frame="none" id="enc-idx-flags">
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<title>Index Entry Flags</title>
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<tgroup cols="3">
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&cs-def;
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<tbody valign="top">
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<row>
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<entry><constant>V4L2_ENC_IDX_FRAME_I</constant></entry>
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<entry>0x00</entry>
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<entry>This is an Intra-coded picture.</entry>
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</row>
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<row>
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<entry><constant>V4L2_ENC_IDX_FRAME_P</constant></entry>
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<entry>0x01</entry>
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<entry>This is a Predictive-coded picture.</entry>
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</row>
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<row>
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<entry><constant>V4L2_ENC_IDX_FRAME_B</constant></entry>
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<entry>0x02</entry>
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<entry>This is a Bidirectionally predictive-coded
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picture.</entry>
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</row>
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<row>
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<entry><constant>V4L2_ENC_IDX_FRAME_MASK</constant></entry>
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<entry>0x0F</entry>
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<entry><wordasword>AND</wordasword> the flags field with
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this mask to obtain the picture coding type.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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</refsect1>
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<refsect1>
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&return-value;
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</refsect1>
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</refentry>
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