dev-sliced-vbi.xml

  <title>Sliced VBI Data Interface</title>

  <para>VBI stands for Vertical Blanking Interval, a gap in the
sequence of lines of an analog video signal. During VBI no picture
information is transmitted, allowing some time while the electron beam
of a cathode ray tube TV returns to the top of the screen.</para>

  <para>Sliced VBI devices use hardware to demodulate data transmitted
in the VBI. V4L2 drivers shall <emphasis>not</emphasis> do this by
software, see also the <link linkend="raw-vbi">raw VBI
interface</link>. The data is passed as short packets of fixed size,
covering one scan line each. The number of packets per video frame is
variable.</para>

  <para>Sliced VBI capture and output devices are accessed through the
same character special files as raw VBI devices. When a driver
supports both interfaces, the default function of a
<filename>/dev/vbi</filename> device is <emphasis>raw</emphasis> VBI
capturing or output, and the sliced VBI function is only available
after calling the &VIDIOC-S-FMT; ioctl as defined below. Likewise a
<filename>/dev/video</filename> device may support the sliced VBI API,
however the default function here is video capturing or output.
Different file descriptors must be used to pass raw and sliced VBI
data simultaneously, if this is supported by the driver.</para>

  <section>
    <title>Querying Capabilities</title>

    <para>Devices supporting the sliced VBI capturing or output API
set the <constant>V4L2_CAP_SLICED_VBI_CAPTURE</constant> or
<constant>V4L2_CAP_SLICED_VBI_OUTPUT</constant> flag respectively, in
the <structfield>capabilities</structfield> field of &v4l2-capability;
returned by the &VIDIOC-QUERYCAP; ioctl. At least one of the
read/write, streaming or asynchronous <link linkend="io">I/O
methods</link> must be supported. Sliced VBI devices may have a tuner
or modulator.</para>
  </section>

  <section>
    <title>Supplemental Functions</title>

    <para>Sliced VBI devices shall support <link linkend="video">video
input or output</link> and <link linkend="tuner">tuner or
modulator</link> ioctls if they have these capabilities, and they may
support <link linkend="control">control</link> ioctls. The <link
linkend="standard">video standard</link> ioctls provide information
vital to program a sliced VBI device, therefore must be
supported.</para>
  </section>

  <section id="sliced-vbi-format-negotitation">
    <title>Sliced VBI Format Negotiation</title>

    <para>To find out which data services are supported by the
hardware applications can call the &VIDIOC-G-SLICED-VBI-CAP; ioctl.
All drivers implementing the sliced VBI interface must support this
ioctl. The results may differ from those of the &VIDIOC-S-FMT; ioctl
when the number of VBI lines the hardware can capture or output per
frame, or the number of services it can identify on a given line are
limited. For example on PAL line 16 the hardware may be able to look
for a VPS or Teletext signal, but not both at the same time.</para>

    <para>To determine the currently selected services applications
set the <structfield>type </structfield> field of &v4l2-format; to
<constant> V4L2_BUF_TYPE_SLICED_VBI_CAPTURE</constant> or <constant>
V4L2_BUF_TYPE_SLICED_VBI_OUTPUT</constant>, and the &VIDIOC-G-FMT;
ioctl fills the <structfield>fmt.sliced</structfield> member, a
&v4l2-sliced-vbi-format;.</para>

    <para>Applications can request different parameters by
initializing or modifying the <structfield>fmt.sliced</structfield>
member and calling the &VIDIOC-S-FMT; ioctl with a pointer to the
<structname>v4l2_format</structname> structure.</para>

    <para>The sliced VBI API is more complicated than the raw VBI API
because the hardware must be told which VBI service to expect on each
scan line. Not all services may be supported by the hardware on all
lines (this is especially true for VBI output where Teletext is often
unsupported and other services can only be inserted in one specific
line). In many cases, however, it is sufficient to just set the
<structfield>service_set</structfield> field to the required services
and let the driver fill the <structfield>service_lines</structfield>
array according to hardware capabilities. Only if more precise control
is needed should the programmer set the
<structfield>service_lines</structfield> array explicitly.</para>

    <para>The &VIDIOC-S-FMT; ioctl modifies the parameters
according to hardware capabilities. When the driver allocates
resources at this point, it may return an &EBUSY; if the required
resources are temporarily unavailable. Other resource allocation
points which may return <errorcode>EBUSY</errorcode> can be the
&VIDIOC-STREAMON; ioctl and the first &func-read;, &func-write; and
&func-select; call.</para>

    <table frame="none" pgwide="1" id="v4l2-sliced-vbi-format">
      <title>struct
<structname>v4l2_sliced_vbi_format</structname></title>
      <tgroup cols="5">
	<colspec colname="c1" colwidth="3*" />
	<colspec colname="c2" colwidth="3*" />
	<colspec colname="c3" colwidth="2*" />
	<colspec colname="c4" colwidth="2*" />
	<colspec colname="c5" colwidth="2*" />
	<spanspec namest="c3" nameend="c5" spanname="hspan" />
	<tbody valign="top">
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>service_set</structfield></entry>
	    <entry spanname="hspan"><para>If
<structfield>service_set</structfield> is non-zero when passed with
&VIDIOC-S-FMT; or &VIDIOC-TRY-FMT;, the
<structfield>service_lines</structfield> array will be filled by the
driver according to the services specified in this field. For example,
if <structfield>service_set</structfield> is initialized with
<constant>V4L2_SLICED_TELETEXT_B | V4L2_SLICED_WSS_625</constant>, a
driver for the cx25840 video decoder sets lines 7-22 of both
fields<footnote><para>According to <link
linkend="ets300706">ETS&nbsp;300&nbsp;706</link> lines 6-22 of the
first field and lines 5-22 of the second field may carry Teletext
data.</para></footnote> to <constant>V4L2_SLICED_TELETEXT_B</constant>
and line 23 of the first field to
<constant>V4L2_SLICED_WSS_625</constant>. If
<structfield>service_set</structfield> is set to zero, then the values
of <structfield>service_lines</structfield> will be used instead.
</para><para>On return the driver sets this field to the union of all
elements of the returned <structfield>service_lines</structfield>
array. It may contain less services than requested, perhaps just one,
if the hardware cannot handle more services simultaneously. It may be
empty (zero) if none of the requested services are supported by the
hardware.</para></entry>
	  </row>
	  <row>
	    <entry>__u16</entry>
	    <entry><structfield>service_lines</structfield>[2][24]</entry>
	    <entry spanname="hspan"><para>Applications initialize this
array with sets of data services the driver shall look for or insert
on the respective scan line. Subject to hardware capabilities drivers
return the requested set, a subset, which may be just a single
service, or an empty set. When the hardware cannot handle multiple
services on the same line the driver shall choose one. No assumptions
can be made on which service the driver chooses.</para><para>Data
services are defined in <xref linkend="vbi-services2" />. Array indices
map to ITU-R line numbers (see also <xref linkend="vbi-525" /> and <xref
		  linkend="vbi-625" />) as follows: <!-- No nested
tables, sigh. --></para></entry>
	  </row>
	  <row>
	    <entry></entry>
	    <entry></entry>
	    <entry>Element</entry>
	    <entry>525 line systems</entry>
	    <entry>625 line systems</entry>
	  </row>
	  <row>
	    <entry></entry>
	    <entry></entry>
	    <entry><structfield>service_lines</structfield>[0][1]</entry>
	    <entry align="center">1</entry>
	    <entry align="center">1</entry>
	  </row>
	  <row>
	    <entry></entry>
	    <entry></entry>
	    <entry><structfield>service_lines</structfield>[0][23]</entry>
	    <entry align="center">23</entry>
	    <entry align="center">23</entry>
	  </row>
	  <row>
	    <entry></entry>
	    <entry></entry>
	    <entry><structfield>service_lines</structfield>[1][1]</entry>
	    <entry align="center">264</entry>
	    <entry align="center">314</entry>
	  </row>
	  <row>
	    <entry></entry>
	    <entry></entry>
	    <entry><structfield>service_lines</structfield>[1][23]</entry>
	    <entry align="center">286</entry>
	    <entry align="center">336</entry>
	  </row>
	  <!-- End of line numbers table. -->
	  <row>
	    <entry></entry>
	    <entry></entry>
	    <entry spanname="hspan">Drivers must set
<structfield>service_lines</structfield>[0][0] and
<structfield>service_lines</structfield>[1][0] to zero.</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>io_size</structfield></entry>
	    <entry spanname="hspan">Maximum number of bytes passed by
one &func-read; or &func-write; call, and the buffer size in bytes for
the &VIDIOC-QBUF; and &VIDIOC-DQBUF; ioctl. Drivers set this field to
the size of &v4l2-sliced-vbi-data; times the number of non-zero
elements in the returned <structfield>service_lines</structfield>
array (that is the number of lines potentially carrying data).</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>reserved</structfield>[2]</entry>
	    <entry spanname="hspan">This array is reserved for future
extensions. Applications and drivers must set it to zero.</entry>
	  </row>
	</tbody>
      </tgroup>
    </table>

    <!-- See also vidioc-g-sliced-vbi-cap.sgml -->
    <table frame="none" pgwide="1" id="vbi-services2">
      <title>Sliced VBI services</title>
      <tgroup cols="5">
	<colspec colname="c1" colwidth="2*" />
	<colspec colname="c2" colwidth="1*" />
	<colspec colname="c3" colwidth="1*" />
	<colspec colname="c4" colwidth="2*" />
	<colspec colname="c5" colwidth="2*" />
	<spanspec namest="c3" nameend="c5" spanname="rlp" />
	<thead>
	  <row>
	    <entry>Symbol</entry>
	    <entry>Value</entry>
	    <entry>Reference</entry>
	    <entry>Lines, usually</entry>
	    <entry>Payload</entry>
	  </row>
	</thead>
	<tbody valign="top">
	  <row>
	    <entry><constant>V4L2_SLICED_TELETEXT_B</constant>
(Teletext System B)</entry>
	    <entry>0x0001</entry>
	    <entry><xref linkend="ets300706" />, <xref linkend="itu653" /></entry>
	    <entry>PAL/SECAM line 7-22, 320-335 (second field 7-22)</entry>
	    <entry>Last 42 of the 45 byte Teletext packet, that is
without clock run-in and framing code, lsb first transmitted.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_SLICED_VPS</constant></entry>
	    <entry>0x0400</entry>
	    <entry><xref linkend="ets300231" /></entry>
	    <entry>PAL line 16</entry>
	    <entry>Byte number 3 to 15 according to Figure 9 of
ETS&nbsp;300&nbsp;231, lsb first transmitted.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_SLICED_CAPTION_525</constant></entry>
	    <entry>0x1000</entry>
	    <entry><xref linkend="eia608" /></entry>
	    <entry>NTSC line 21, 284 (second field 21)</entry>
	    <entry>Two bytes in transmission order, including parity
bit, lsb first transmitted.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_SLICED_WSS_625</constant></entry>
	    <entry>0x4000</entry>
	    <entry><xref linkend="itu1119" />, <xref linkend="en300294" /></entry>
	    <entry>PAL/SECAM line 23</entry>
	    <entry><screen>
Byte         0                 1
      msb         lsb  msb           lsb
 Bit  7 6 5 4 3 2 1 0  x x 13 12 11 10 9
</screen></entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_SLICED_VBI_525</constant></entry>
	    <entry>0x1000</entry>
	    <entry spanname="rlp">Set of services applicable to 525
line systems.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_SLICED_VBI_625</constant></entry>
	    <entry>0x4401</entry>
	    <entry spanname="rlp">Set of services applicable to 625
line systems.</entry>
	  </row>
	</tbody>
      </tgroup>
    </table>

    <para>Drivers may return an &EINVAL; when applications attempt to
read or write data without prior format negotiation, after switching
the video standard (which may invalidate the negotiated VBI
parameters) and after switching the video input (which may change the
video standard as a side effect). The &VIDIOC-S-FMT; ioctl may return
an &EBUSY; when applications attempt to change the format while i/o is
in progress (between a &VIDIOC-STREAMON; and &VIDIOC-STREAMOFF; call,
and after the first &func-read; or &func-write; call).</para>
  </section>

  <section>
    <title>Reading and writing sliced VBI data</title>

    <para>A single &func-read; or &func-write; call must pass all data
belonging to one video frame. That is an array of
<structname>v4l2_sliced_vbi_data</structname> structures with one or
more elements and a total size not exceeding
<structfield>io_size</structfield> bytes. Likewise in streaming I/O
mode one buffer of <structfield>io_size</structfield> bytes must
contain data of one video frame. The <structfield>id</structfield> of
unused <structname>v4l2_sliced_vbi_data</structname> elements must be
zero.</para>

    <table frame="none" pgwide="1" id="v4l2-sliced-vbi-data">
      <title>struct
<structname>v4l2_sliced_vbi_data</structname></title>
      <tgroup cols="3">
	&cs-def;
	<tbody valign="top">
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>id</structfield></entry>
	    <entry>A flag from <xref linkend="vbi-services" />
identifying the type of data in this packet. Only a single bit must be
set. When the <structfield>id</structfield> of a captured packet is
zero, the packet is empty and the contents of other fields are
undefined. Applications shall ignore empty packets. When the
<structfield>id</structfield> of a packet for output is zero the
contents of the <structfield>data</structfield> field are undefined
and the driver must no longer insert data on the requested
<structfield>field</structfield> and
<structfield>line</structfield>.</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>field</structfield></entry>
	    <entry>The video field number this data has been captured
from, or shall be inserted at. <constant>0</constant> for the first
field, <constant>1</constant> for the second field.</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>line</structfield></entry>
	    <entry>The field (as opposed to frame) line number this
data has been captured from, or shall be inserted at. See <xref
	    linkend="vbi-525" /> and <xref linkend="vbi-625" /> for valid
values. Sliced VBI capture devices can set the line number of all
packets to <constant>0</constant> if the hardware cannot reliably
identify scan lines. The field number must always be valid.</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>reserved</structfield></entry>
	    <entry>This field is reserved for future extensions.
Applications and drivers must set it to zero.</entry>
	  </row>
	  <row>
	    <entry>__u8</entry>
	    <entry><structfield>data</structfield>[48]</entry>
	    <entry>The packet payload. See <xref
	    linkend="vbi-services" /> for the contents and number of
bytes passed for each data type. The contents of padding bytes at the
end of this array are undefined, drivers and applications shall ignore
them.</entry>
	  </row>
	</tbody>
      </tgroup>
    </table>

    <para>Packets are always passed in ascending line number order,
without duplicate line numbers. The &func-write; function and the
&VIDIOC-QBUF; ioctl must return an &EINVAL; when applications violate
this rule. They must also return an &EINVAL; when applications pass an
incorrect field or line number, or a combination of
<structfield>field</structfield>, <structfield>line</structfield> and
<structfield>id</structfield> which has not been negotiated with the
&VIDIOC-G-FMT; or &VIDIOC-S-FMT; ioctl. When the line numbers are
unknown the driver must pass the packets in transmitted order. The
driver can insert empty packets with <structfield>id</structfield> set
to zero anywhere in the packet array.</para>

    <para>To assure synchronization and to distinguish from frame
dropping, when a captured frame does not carry any of the requested
data services drivers must pass one or more empty packets. When an
application fails to pass VBI data in time for output, the driver
must output the last VPS and WSS packet again, and disable the output
of Closed Caption and Teletext data, or output data which is ignored
by Closed Caption and Teletext decoders.</para>

    <para>A sliced VBI device may support <link
linkend="rw">read/write</link> and/or streaming (<link
linkend="mmap">memory mapping</link> and/or <link linkend="userp">user
pointer</link>) I/O. The latter bears the possibility of synchronizing
video and VBI data by using buffer timestamps.</para>

  </section>

  <section>
    <title>Sliced VBI Data in MPEG Streams</title>

    <para>If a device can produce an MPEG output stream, it may be
capable of providing <link
linkend="sliced-vbi-format-negotitation">negotiated sliced VBI
services</link> as data embedded in the MPEG stream.  Users or
applications control this sliced VBI data insertion with the <link
linkend="v4l2-mpeg-stream-vbi-fmt">V4L2_CID_MPEG_STREAM_VBI_FMT</link>
control.</para>

    <para>If the driver does not provide the <link
linkend="v4l2-mpeg-stream-vbi-fmt">V4L2_CID_MPEG_STREAM_VBI_FMT</link>
control, or only allows that control to be set to <link
linkend="v4l2-mpeg-stream-vbi-fmt"><constant>
V4L2_MPEG_STREAM_VBI_FMT_NONE</constant></link>, then the device
cannot embed sliced VBI data in the MPEG stream.</para>

    <para>The <link linkend="v4l2-mpeg-stream-vbi-fmt">
V4L2_CID_MPEG_STREAM_VBI_FMT</link> control does not implicitly set
the device driver to capture nor cease capturing sliced VBI data.  The
control only indicates to embed sliced VBI data in the MPEG stream, if
an application has negotiated sliced VBI service be captured.</para>

    <para>It may also be the case that a device can embed sliced VBI
data in only certain types of MPEG streams: for example in an MPEG-2
PS but not an MPEG-2 TS.  In this situation, if sliced VBI data
insertion is requested, the sliced VBI data will be embedded in MPEG
stream types when supported, and silently omitted from MPEG stream
types where sliced VBI data insertion is not supported by the device.
</para>

    <para>The following subsections specify the format of the
embedded sliced VBI data.</para>

  <section>
    <title>MPEG Stream Embedded, Sliced VBI Data Format: NONE</title>
    <para>The <link linkend="v4l2-mpeg-stream-vbi-fmt"><constant>
V4L2_MPEG_STREAM_VBI_FMT_NONE</constant></link> embedded sliced VBI
format shall be interpreted by drivers as a control to cease
embedding sliced VBI data in MPEG streams.  Neither the device nor
driver shall insert "empty" embedded sliced VBI data packets in the
MPEG stream when this format is set.  No MPEG stream data structures
are specified for this format.</para>
  </section>

  <section>
    <title>MPEG Stream Embedded, Sliced VBI Data Format: IVTV</title>
    <para>The <link linkend="v4l2-mpeg-stream-vbi-fmt"><constant>
V4L2_MPEG_STREAM_VBI_FMT_IVTV</constant></link> embedded sliced VBI
format, when supported, indicates to the driver to embed up to 36
lines of sliced VBI data per frame in an MPEG-2 <emphasis>Private
Stream 1 PES</emphasis> packet encapsulated in an MPEG-2 <emphasis>
Program Pack</emphasis> in the MPEG stream.</para>

    <para><emphasis>Historical context</emphasis>: This format
specification originates from a custom, embedded, sliced VBI data
format used by the <filename>ivtv</filename> driver.  This format
has already been informally specified in the kernel sources in the
file <filename>Documentation/video4linux/cx2341x/README.vbi</filename>
.  The maximum size of the payload and other aspects of this format
are driven by the CX23415 MPEG decoder's capabilities and limitations
with respect to extracting, decoding, and displaying sliced VBI data
embedded within an MPEG stream.</para>

    <para>This format's use is <emphasis>not</emphasis> exclusive to
the <filename>ivtv</filename> driver <emphasis>nor</emphasis>
exclusive to CX2341x devices, as the sliced VBI data packet insertion
into the MPEG stream is implemented in driver software.  At least the
<filename>cx18</filename> driver provides sliced VBI data insertion
into an MPEG-2 PS in this format as well.</para>

    <para>The following definitions specify the payload of the
MPEG-2 <emphasis>Private Stream 1 PES</emphasis> packets that contain
sliced VBI data when <link linkend="v4l2-mpeg-stream-vbi-fmt">
<constant>V4L2_MPEG_STREAM_VBI_FMT_IVTV</constant></link> is set.
(The MPEG-2 <emphasis>Private Stream 1 PES</emphasis> packet header
and encapsulating MPEG-2 <emphasis>Program Pack</emphasis> header are
not detailed here.  Please refer to the MPEG-2 specifications for
details on those packet headers.)</para>

    <para>The payload of the MPEG-2 <emphasis>Private Stream 1 PES
</emphasis> packets that contain sliced VBI data is specified by
&v4l2-mpeg-vbi-fmt-ivtv;.  The payload is variable
length, depending on the actual number of lines of sliced VBI data
present in a video frame.  The payload may be padded at the end with
unspecified fill bytes to align the end of the payload to a 4-byte
boundary.  The payload shall never exceed 1552 bytes (2 fields with
18 lines/field with 43 bytes of data/line and a 4 byte magic number).
</para>

    <table frame="none" pgwide="1" id="v4l2-mpeg-vbi-fmt-ivtv">
      <title>struct <structname>v4l2_mpeg_vbi_fmt_ivtv</structname>
      </title>
      <tgroup cols="4">
	&cs-ustr;
	<tbody valign="top">
	  <row>
	    <entry>__u8</entry>
	    <entry><structfield>magic</structfield>[4]</entry>
	    <entry></entry>
	    <entry>A "magic" constant from <xref
	    linkend="v4l2-mpeg-vbi-fmt-ivtv-magic" /> that indicates
this is a valid sliced VBI data payload and also indicates which
member of the anonymous union, <structfield>itv0</structfield> or
<structfield>ITV0</structfield>, to use for the payload data.</entry>
	  </row>
	  <row>
	    <entry>union</entry>
	    <entry>(anonymous)</entry>
	  </row>
	  <row>
	    <entry></entry>
	    <entry>struct <link linkend="v4l2-mpeg-vbi-itv0">
	      <structname>v4l2_mpeg_vbi_itv0</structname></link>
	    </entry>
	    <entry><structfield>itv0</structfield></entry>
	    <entry>The primary form of the sliced VBI data payload
that contains anywhere from 1 to 35 lines of sliced VBI data.
Line masks are provided in this form of the payload indicating
which VBI lines are provided.</entry>
	  </row>
	  <row>
	    <entry></entry>
	    <entry>struct <link linkend="v4l2-mpeg-vbi-itv0-1">
	      <structname>v4l2_mpeg_vbi_ITV0</structname></link>
	    </entry>
	    <entry><structfield>ITV0</structfield></entry>
	    <entry>An alternate form of the sliced VBI data payload
used when 36 lines of sliced VBI data are present.  No line masks are
provided in this form of the payload; all valid line mask bits are
implcitly set.</entry>
	  </row>
	</tbody>
      </tgroup>
    </table>

    <table frame="none" pgwide="1" id="v4l2-mpeg-vbi-fmt-ivtv-magic">
      <title>Magic Constants for &v4l2-mpeg-vbi-fmt-ivtv;
	<structfield>magic</structfield> field</title>
      <tgroup cols="3">
	&cs-def;
	<thead>
	  <row>
	    <entry align="left">Defined Symbol</entry>
	    <entry align="left">Value</entry>
	    <entry align="left">Description</entry>
	  </row>
	</thead>
	<tbody valign="top">
	  <row>
	    <entry><constant>V4L2_MPEG_VBI_IVTV_MAGIC0</constant>
	    </entry>
	    <entry>"itv0"</entry>
	    <entry>Indicates the <structfield>itv0</structfield>
member of the union in &v4l2-mpeg-vbi-fmt-ivtv; is valid.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_MPEG_VBI_IVTV_MAGIC1</constant>
	    </entry>
	    <entry>"ITV0"</entry>
	    <entry>Indicates the <structfield>ITV0</structfield>
member of the union in &v4l2-mpeg-vbi-fmt-ivtv; is valid and
that 36 lines of sliced VBI data are present.</entry>
	  </row>
	</tbody>
      </tgroup>
    </table>

    <table frame="none" pgwide="1" id="v4l2-mpeg-vbi-itv0">
      <title>struct <structname>v4l2_mpeg_vbi_itv0</structname>
      </title>
      <tgroup cols="3">
	&cs-str;
	<tbody valign="top">
	  <row>
	    <entry>__le32</entry>
	    <entry><structfield>linemask</structfield>[2]</entry>
	    <entry><para>Bitmasks indicating the VBI service lines
present.  These <structfield>linemask</structfield> values are stored
in little endian byte order in the MPEG stream.  Some reference
<structfield>linemask</structfield> bit positions with their
corresponding VBI line number and video field are given below.
b<subscript>0</subscript> indicates the least significant bit of a
<structfield>linemask</structfield> value:<screen>
<structfield>linemask</structfield>[0] b<subscript>0</subscript>:		line  6		first field
<structfield>linemask</structfield>[0] b<subscript>17</subscript>:		line 23		first field
<structfield>linemask</structfield>[0] b<subscript>18</subscript>:		line  6		second field
<structfield>linemask</structfield>[0] b<subscript>31</subscript>:		line 19		second field
<structfield>linemask</structfield>[1] b<subscript>0</subscript>:		line 20		second field
<structfield>linemask</structfield>[1] b<subscript>3</subscript>:		line 23		second field
<structfield>linemask</structfield>[1] b<subscript>4</subscript>-b<subscript>31</subscript>:	unused and set to 0</screen></para></entry>
	  </row>
	  <row>
	    <entry>struct <link linkend="v4l2-mpeg-vbi-itv0-line">
	      <structname>v4l2_mpeg_vbi_itv0_line</structname></link>
	    </entry>
	    <entry><structfield>line</structfield>[35]</entry>
	    <entry>This is a variable length array that holds from 1
to 35 lines of sliced VBI data.  The sliced VBI data lines present
correspond to the bits set in the <structfield>linemask</structfield>
array, starting from b<subscript>0</subscript> of <structfield>
linemask</structfield>[0] up through b<subscript>31</subscript> of
<structfield>linemask</structfield>[0], and from b<subscript>0
</subscript> of <structfield>linemask</structfield>[1] up through b
<subscript>3</subscript> of <structfield>linemask</structfield>[1].
<structfield>line</structfield>[0] corresponds to the first bit
found set in the <structfield>linemask</structfield> array,
<structfield>line</structfield>[1] corresponds to the second bit
found set in the <structfield>linemask</structfield> array, etc.
If no <structfield>linemask</structfield> array bits are set, then
<structfield>line</structfield>[0] may contain one line of
unspecified data that should be ignored by applications.</entry>
	  </row>
	</tbody>
      </tgroup>
    </table>

    <table frame="none" pgwide="1" id="v4l2-mpeg-vbi-itv0-1">
      <title>struct <structname>v4l2_mpeg_vbi_ITV0</structname>
      </title>
      <tgroup cols="3">
	&cs-str;
	<tbody valign="top">
	  <row>
	    <entry>struct <link linkend="v4l2-mpeg-vbi-itv0-line">
	      <structname>v4l2_mpeg_vbi_itv0_line</structname></link>
	    </entry>
	    <entry><structfield>line</structfield>[36]</entry>
	    <entry>A fixed length array of 36 lines of sliced VBI
data.  <structfield>line</structfield>[0] through <structfield>line
</structfield>[17] correspond to lines 6 through 23 of the
first field.  <structfield>line</structfield>[18] through
<structfield>line</structfield>[35] corresponds to lines 6
through 23 of the second field.</entry>
	  </row>
	</tbody>
      </tgroup>
    </table>

    <table frame="none" pgwide="1" id="v4l2-mpeg-vbi-itv0-line">
      <title>struct <structname>v4l2_mpeg_vbi_itv0_line</structname>
      </title>
      <tgroup cols="3">
	&cs-str;
	<tbody valign="top">
	  <row>
	    <entry>__u8</entry>
	    <entry><structfield>id</structfield></entry>
	    <entry>A line identifier value from
<xref linkend="ITV0-Line-Identifier-Constants" /> that indicates
the type of sliced VBI data stored on this line.</entry>
	  </row>
	  <row>
	    <entry>__u8</entry>
	    <entry><structfield>data</structfield>[42]</entry>
	    <entry>The sliced VBI data for the line.</entry>
	  </row>
	</tbody>
      </tgroup>
    </table>

    <table frame="none" pgwide="1" id="ITV0-Line-Identifier-Constants">
      <title>Line Identifiers for struct <link
      linkend="v4l2-mpeg-vbi-itv0-line"><structname>
v4l2_mpeg_vbi_itv0_line</structname></link> <structfield>id
</structfield> field</title>
      <tgroup cols="3">
	&cs-def;
	<thead>
	  <row>
	    <entry align="left">Defined Symbol</entry>
	    <entry align="left">Value</entry>
	    <entry align="left">Description</entry>
	  </row>
	</thead>
	<tbody valign="top">
	  <row>
	    <entry><constant>V4L2_MPEG_VBI_IVTV_TELETEXT_B</constant>
	    </entry>
	    <entry>1</entry>
	    <entry>Refer to <link linkend="vbi-services2">
Sliced VBI services</link> for a description of the line payload.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_MPEG_VBI_IVTV_CAPTION_525</constant>
	    </entry>
	    <entry>4</entry>
	    <entry>Refer to <link linkend="vbi-services2">
Sliced VBI services</link> for a description of the line payload.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_MPEG_VBI_IVTV_WSS_625</constant>
	    </entry>
	    <entry>5</entry>
	    <entry>Refer to <link linkend="vbi-services2">
Sliced VBI services</link> for a description of the line payload.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_MPEG_VBI_IVTV_VPS</constant>
	    </entry>
	    <entry>7</entry>
	    <entry>Refer to <link linkend="vbi-services2">
Sliced VBI services</link> for a description of the line payload.</entry>
	  </row>
	</tbody>
      </tgroup>
    </table>

  </section>
  </section>


<!--
Local Variables:
mode: sgml
sgml-parent-document: "v4l2.sgml"
indent-tabs-mode: nil
End:
 -->