doc/spec/r10211.htm

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>Video for Linux Two API Specification: Revision 0.24</TH
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><H1
><A
NAME="VIDIOC-G-ENC-INDEX"
></A
>ioctl VIDIOC_G_ENC_INDEX</H1
><DIV
CLASS="REFNAMEDIV"
><A
NAME="AEN10215"
></A
><H2
>Name</H2
>VIDIOC_G_ENC_INDEX&nbsp;--&nbsp;Get meta data about a compressed video stream</DIV
><DIV
CLASS="REFSYNOPSISDIV"
><A
NAME="AEN10218"
></A
><H2
>Synopsis</H2
><DIV
CLASS="FUNCSYNOPSIS"
><P
></P
><A
NAME="AEN10219"
></A
><P
><CODE
><CODE
CLASS="FUNCDEF"
>int ioctl</CODE
>(int fd, int request, struct v4l2_enc_idx *argp);</CODE
></P
><P
></P
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN10229"
></A
><H2
>Arguments</H2
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><CODE
CLASS="PARAMETER"
>fd</CODE
></DT
><DD
><P
>File descriptor returned by <A
HREF="r14090.htm"
><CODE
CLASS="FUNCTION"
>open()</CODE
></A
>.</P
></DD
><DT
><CODE
CLASS="PARAMETER"
>request</CODE
></DT
><DD
><P
>VIDIOC_G_ENC_INDEX</P
></DD
><DT
><CODE
CLASS="PARAMETER"
>argp</CODE
></DT
><DD
><P
></P
></DD
></DL
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN10249"
></A
><H2
>Description</H2
><DIV
CLASS="NOTE"
><BLOCKQUOTE
CLASS="NOTE"
><P
><B
>Experimental: </B
>This is an <A
HREF="x16453.htm"
>experimental</A
>
interface and may change in the future.</P
></BLOCKQUOTE
></DIV
><P
>The <CODE
CLASS="CONSTANT"
>VIDIOC_G_ENC_INDEX</CODE
> 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.</P
><P
>To read the data applications must call
<CODE
CLASS="CONSTANT"
>VIDIOC_G_ENC_INDEX</CODE
> with a pointer to a
struct&nbsp;<A
HREF="r10211.htm#V4L2-ENC-IDX"
>v4l2_enc_idx</A
>. On success the driver fills the
<CODE
CLASS="STRUCTFIELD"
>entry</CODE
> array, stores the number of elements
written in the <CODE
CLASS="STRUCTFIELD"
>entries</CODE
> field, and
initializes the <CODE
CLASS="STRUCTFIELD"
>entries_cap</CODE
> field.</P
><P
>Each element of the <CODE
CLASS="STRUCTFIELD"
>entry</CODE
> array
contains meta data about one picture. A
<CODE
CLASS="CONSTANT"
>VIDIOC_G_ENC_INDEX</CODE
> call reads up to
<CODE
CLASS="CONSTANT"
>V4L2_ENC_IDX_ENTRIES</CODE
> entries from a driver
buffer, which can hold up to <CODE
CLASS="STRUCTFIELD"
>entries_cap</CODE
>
entries. This number can be lower or higher than
<CODE
CLASS="CONSTANT"
>V4L2_ENC_IDX_ENTRIES</CODE
>, 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, <CODE
CLASS="STRUCTFIELD"
>entries</CODE
> will be zero.</P
><P
>Currently this ioctl is only defined for MPEG-2 program
streams and video elementary streams.</P
><DIV
CLASS="TABLE"
><A
NAME="V4L2-ENC-IDX"
></A
><P
><B
>Table 1. struct <CODE
CLASS="STRUCTNAME"
>v4l2_enc_idx</CODE
></B
></P
><TABLE
BORDER="0"
FRAME="void"
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><COL
WIDTH="25%"
TITLE="C1"><COL
WIDTH="25%"
TITLE="C2"><COL
WIDTH="50%"
TITLE="C3"><TBODY
VALIGN="TOP"
><TR
><TD
>__u32</TD
><TD
><CODE
CLASS="STRUCTFIELD"
>entries</CODE
></TD
><TD
>The number of entries the driver stored in the
<CODE
CLASS="STRUCTFIELD"
>entry</CODE
> array.</TD
></TR
><TR
><TD
>__u32</TD
><TD
><CODE
CLASS="STRUCTFIELD"
>entries_cap</CODE
></TD
><TD
>The number of entries the driver can
buffer. Must be greater than zero.</TD
></TR
><TR
><TD
>__u32</TD
><TD
><CODE
CLASS="STRUCTFIELD"
>reserved</CODE
>[4]</TD
><TD
COLSPAN="3"
>Reserved for future extensions.
Drivers must set the array to zero.</TD
></TR
><TR
><TD
>struct&nbsp;<A
HREF="r10211.htm#V4L2-ENC-IDX-ENTRY"
>v4l2_enc_idx_entry</A
></TD
><TD
><CODE
CLASS="STRUCTFIELD"
>entry</CODE
>[<CODE
CLASS="CONSTANT"
>V4L2_ENC_IDX_ENTRIES</CODE
>]</TD
><TD
>Meta data about a compressed video stream. Each
element of the array corresponds to one picture, sorted in ascending
order by their <CODE
CLASS="STRUCTFIELD"
>offset</CODE
>.</TD
></TR
></TBODY
></TABLE
></DIV
><DIV
CLASS="TABLE"
><A
NAME="V4L2-ENC-IDX-ENTRY"
></A
><P
><B
>Table 2. struct <CODE
CLASS="STRUCTNAME"
>v4l2_enc_idx_entry</CODE
></B
></P
><TABLE
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><TR
><TD
>__u64</TD
><TD
><CODE
CLASS="STRUCTFIELD"
>offset</CODE
></TD
><TD
>The offset in bytes from the beginning of the
compressed video stream to the beginning of this picture, that is a
<I
CLASS="WORDASWORD"
>PES packet header</I
> as defined in <A
HREF="b17127.htm#MPEG2PART1"
><ABBR
CLASS="ABBREV"
>ISO&nbsp;13818-1</ABBR
></A
> or a <I
CLASS="WORDASWORD"
>picture
header</I
> as defined in <A
HREF="b17127.htm#MPEG2PART2"
><ABBR
CLASS="ABBREV"
>ISO&nbsp;13818-2</ABBR
></A
>. When
the encoder is stopped, the driver resets the offset to zero.</TD
></TR
><TR
><TD
>__u64</TD
><TD
><CODE
CLASS="STRUCTFIELD"
>pts</CODE
></TD
><TD
>The 33 bit <I
CLASS="WORDASWORD"
>Presentation Time
Stamp</I
> of this picture as defined in <A
HREF="b17127.htm#MPEG2PART1"
><ABBR
CLASS="ABBREV"
>ISO&nbsp;13818-1</ABBR
></A
>.</TD
></TR
><TR
><TD
>__u32</TD
><TD
><CODE
CLASS="STRUCTFIELD"
>length</CODE
></TD
><TD
>The length of this picture in bytes.</TD
></TR
><TR
><TD
>__u32</TD
><TD
><CODE
CLASS="STRUCTFIELD"
>flags</CODE
></TD
><TD
>Flags containing the coding type of this picture, see <A
HREF="r10211.htm#ENC-IDX-FLAGS"
>Table 3</A
>.</TD
></TR
><TR
><TD
>__u32</TD
><TD
><CODE
CLASS="STRUCTFIELD"
>reserved</CODE
>[2]</TD
><TD
>Reserved for future extensions.
Drivers must set the array to zero.</TD
></TR
></TBODY
></TABLE
></DIV
><DIV
CLASS="TABLE"
><A
NAME="ENC-IDX-FLAGS"
></A
><P
><B
>Table 3. Index Entry Flags</B
></P
><TABLE
BORDER="0"
FRAME="void"
WIDTH="100%"
CLASS="CALSTABLE"
><COL
WIDTH="38%"
TITLE="C1"><COL
WIDTH="12%"
TITLE="C2"><COL
WIDTH="50%"
TITLE="C3"><TBODY
VALIGN="TOP"
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_ENC_IDX_FRAME_I</CODE
></TD
><TD
>0x00</TD
><TD
>This is an Intra-coded picture.</TD
></TR
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_ENC_IDX_FRAME_P</CODE
></TD
><TD
>0x01</TD
><TD
>This is a Predictive-coded picture.</TD
></TR
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_ENC_IDX_FRAME_B</CODE
></TD
><TD
>0x02</TD
><TD
>This is a Bidirectionally predictive-coded
picture.</TD
></TR
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_ENC_IDX_FRAME_MASK</CODE
></TD
><TD
>0x0F</TD
><TD
><I
CLASS="WORDASWORD"
>AND</I
> the flags field with
this mask to obtain the picture coding type.</TD
></TR
></TBODY
></TABLE
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN10374"
></A
><H2
>Return Value</H2
><P
>On success <SPAN
CLASS="RETURNVALUE"
>0</SPAN
> is returned, on error <SPAN
CLASS="RETURNVALUE"
>-1</SPAN
> and the <CODE
CLASS="VARNAME"
>errno</CODE
> variable is set appropriately:</P
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><SPAN
CLASS="ERRORCODE"
>EINVAL</SPAN
></DT
><DD
><P
>The driver does not support this ioctl.</P
></DD
></DL
></DIV
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