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diff --git a/Documentation/userspace-api/media/v4l/dev-sliced-vbi.rst b/Documentation/userspace-api/media/v4l/dev-sliced-vbi.rst new file mode 100644 index 000000000..f0df144c9 --- /dev/null +++ b/Documentation/userspace-api/media/v4l/dev-sliced-vbi.rst @@ -0,0 +1,645 @@ +.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later +.. c:namespace:: V4L + +.. _sliced: + +************************* +Sliced VBI Data Interface +************************* + +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. + +Sliced VBI devices use hardware to demodulate data transmitted in the +VBI. V4L2 drivers shall *not* do this by software, see also the +:ref:`raw VBI interface <raw-vbi>`. The data is passed as short +packets of fixed size, covering one scan line each. The number of +packets per video frame is variable. + +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 ``/dev/vbi`` device is *raw* VBI +capturing or output, and the sliced VBI function is only available after +calling the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl as defined +below. Likewise a ``/dev/video`` 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. + +Querying Capabilities +===================== + +Devices supporting the sliced VBI capturing or output API set the +``V4L2_CAP_SLICED_VBI_CAPTURE`` or ``V4L2_CAP_SLICED_VBI_OUTPUT`` flag +respectively, in the ``capabilities`` field of struct +:c:type:`v4l2_capability` returned by the +:ref:`VIDIOC_QUERYCAP` ioctl. At least one of the +read/write, streaming or asynchronous :ref:`I/O methods <io>` must be +supported. Sliced VBI devices may have a tuner or modulator. + +Supplemental Functions +====================== + +Sliced VBI devices shall support :ref:`video input or output <video>` +and :ref:`tuner or modulator <tuner>` ioctls if they have these +capabilities, and they may support :ref:`control` ioctls. +The :ref:`video standard <standard>` ioctls provide information vital +to program a sliced VBI device, therefore must be supported. + +.. _sliced-vbi-format-negotitation: + +Sliced VBI Format Negotiation +============================= + +To find out which data services are supported by the hardware +applications can call the +:ref:`VIDIOC_G_SLICED_VBI_CAP <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 +:ref:`VIDIOC_S_FMT <VIDIOC_G_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. + +To determine the currently selected services applications set the +``type`` field of struct :c:type:`v4l2_format` to +``V4L2_BUF_TYPE_SLICED_VBI_CAPTURE`` or +``V4L2_BUF_TYPE_SLICED_VBI_OUTPUT``, and the +:ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` ioctl fills the ``fmt.sliced`` +member, a struct +:c:type:`v4l2_sliced_vbi_format`. + +Applications can request different parameters by initializing or +modifying the ``fmt.sliced`` member and calling the +:ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl with a pointer to the +struct :c:type:`v4l2_format` structure. + +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 ``service_set`` field +to the required services and let the driver fill the ``service_lines`` +array according to hardware capabilities. Only if more precise control +is needed should the programmer set the ``service_lines`` array +explicitly. + +The :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl modifies the parameters +according to hardware capabilities. When the driver allocates resources +at this point, it may return an ``EBUSY`` error code if the required +resources are temporarily unavailable. Other resource allocation points +which may return ``EBUSY`` can be the +:ref:`VIDIOC_STREAMON` ioctl and the first +:c:func:`read()`, :c:func:`write()` and +:c:func:`select()` call. + +.. c:type:: v4l2_sliced_vbi_format + +struct v4l2_sliced_vbi_format +----------------------------- + +.. raw:: latex + + \begingroup + \scriptsize + \setlength{\tabcolsep}{2pt} + +.. tabularcolumns:: |p{.85cm}|p{3.3cm}|p{4.4cm}|p{4.4cm}|p{4.4cm}| + +.. cssclass:: longtable + +.. flat-table:: + :header-rows: 0 + :stub-columns: 0 + :widths: 3 3 2 2 2 + + * - __u16 + - ``service_set`` + - :cspan:`2` + + If ``service_set`` is non-zero when passed with + :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` or + :ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>`, the ``service_lines`` + array will be filled by the driver according to the services + specified in this field. For example, if ``service_set`` is + initialized with ``V4L2_SLICED_TELETEXT_B | V4L2_SLICED_WSS_625``, + a driver for the cx25840 video decoder sets lines 7-22 of both + fields [#f1]_ to ``V4L2_SLICED_TELETEXT_B`` and line 23 of the first + field to ``V4L2_SLICED_WSS_625``. If ``service_set`` is set to + zero, then the values of ``service_lines`` will be used instead. + + On return the driver sets this field to the union of all elements + of the returned ``service_lines`` 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. + * - __u16 + - ``service_lines``\ [2][24] + - :cspan:`2` + + 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. + + Data services are defined in :ref:`vbi-services2`. Array indices + map to ITU-R line numbers\ [#f2]_ as follows: + * - + - + - Element + - 525 line systems + - 625 line systems + * - + - + - ``service_lines``\ [0][1] + - 1 + - 1 + * - + - + - ``service_lines``\ [0][23] + - 23 + - 23 + * - + - + - ``service_lines``\ [1][1] + - 264 + - 314 + * - + - + - ``service_lines``\ [1][23] + - 286 + - 336 + * - + - + - :cspan:`2` Drivers must set ``service_lines`` [0][0] and + ``service_lines``\ [1][0] to zero. The + ``V4L2_VBI_ITU_525_F1_START``, ``V4L2_VBI_ITU_525_F2_START``, + ``V4L2_VBI_ITU_625_F1_START`` and ``V4L2_VBI_ITU_625_F2_START`` + defines give the start line numbers for each field for each 525 or + 625 line format as a convenience. Don't forget that ITU line + numbering starts at 1, not 0. + * - __u32 + - ``io_size`` + - :cspan:`2` Maximum number of bytes passed by one + :c:func:`read()` or :c:func:`write()` call, + and the buffer size in bytes for the + :ref:`VIDIOC_QBUF` and + :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl. Drivers set this field + to the size of struct + :c:type:`v4l2_sliced_vbi_data` times the + number of non-zero elements in the returned ``service_lines`` + array (that is the number of lines potentially carrying data). + * - __u32 + - ``reserved``\ [2] + - :cspan:`2` This array is reserved for future extensions. + + Applications and drivers must set it to zero. + +.. raw:: latex + + \endgroup + +.. _vbi-services2: + +Sliced VBI services +------------------- + +.. raw:: latex + + \scriptsize + +.. tabularcolumns:: |p{4.1cm}|p{1.1cm}|p{2.4cm}|p{2.0cm}|p{7.3cm}| + +.. flat-table:: + :header-rows: 1 + :stub-columns: 0 + :widths: 2 1 1 2 2 + + * - Symbol + - Value + - Reference + - Lines, usually + - Payload + * - ``V4L2_SLICED_TELETEXT_B`` (Teletext System B) + - 0x0001 + - :ref:`ets300706`, + + :ref:`itu653` + - PAL/SECAM line 7-22, 320-335 (second field 7-22) + - Last 42 of the 45 byte Teletext packet, that is without clock + run-in and framing code, lsb first transmitted. + * - ``V4L2_SLICED_VPS`` + - 0x0400 + - :ref:`ets300231` + - PAL line 16 + - Byte number 3 to 15 according to Figure 9 of ETS 300 231, lsb + first transmitted. + * - ``V4L2_SLICED_CAPTION_525`` + - 0x1000 + - :ref:`cea608` + - NTSC line 21, 284 (second field 21) + - Two bytes in transmission order, including parity bit, lsb first + transmitted. + * - ``V4L2_SLICED_WSS_625`` + - 0x4000 + - :ref:`itu1119`, + + :ref:`en300294` + - PAL/SECAM line 23 + - + + :: + + Byte 0 1 + msb lsb msb lsb + Bit 7 6 5 4 3 2 1 0 x x 13 12 11 10 9 + * - ``V4L2_SLICED_VBI_525`` + - 0x1000 + - :cspan:`2` Set of services applicable to 525 line systems. + * - ``V4L2_SLICED_VBI_625`` + - 0x4401 + - :cspan:`2` Set of services applicable to 625 line systems. + +.. raw:: latex + + \normalsize + +Drivers may return an ``EINVAL`` error code 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 :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl may +return an ``EBUSY`` error code when applications attempt to change the +format while i/o is in progress (between a +:ref:`VIDIOC_STREAMON` and +:ref:`VIDIOC_STREAMOFF <VIDIOC_STREAMON>` call, and after the first +:c:func:`read()` or :c:func:`write()` call). + +Reading and writing sliced VBI data +=================================== + +A single :c:func:`read()` or :c:func:`write()` +call must pass all data belonging to one video frame. That is an array +of struct :c:type:`v4l2_sliced_vbi_data` structures with one or +more elements and a total size not exceeding ``io_size`` bytes. Likewise +in streaming I/O mode one buffer of ``io_size`` bytes must contain data +of one video frame. The ``id`` of unused +struct :c:type:`v4l2_sliced_vbi_data` elements must be zero. + +.. c:type:: v4l2_sliced_vbi_data + +struct v4l2_sliced_vbi_data +--------------------------- + +.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}| + +.. flat-table:: + :header-rows: 0 + :stub-columns: 0 + :widths: 3 1 4 + + * - __u32 + - ``id`` + - A flag from :ref:`vbi-services` identifying the type of data in + this packet. Only a single bit must be set. When the ``id`` 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 ``id`` of a packet for output is zero the + contents of the ``data`` field are undefined and the driver must + no longer insert data on the requested ``field`` and ``line``. + * - __u32 + - ``field`` + - The video field number this data has been captured from, or shall + be inserted at. ``0`` for the first field, ``1`` for the second + field. + * - __u32 + - ``line`` + - The field (as opposed to frame) line number this data has been + captured from, or shall be inserted at. See :ref:`vbi-525` and + :ref:`vbi-625` for valid values. Sliced VBI capture devices can + set the line number of all packets to ``0`` if the hardware cannot + reliably identify scan lines. The field number must always be + valid. + * - __u32 + - ``reserved`` + - This field is reserved for future extensions. Applications and + drivers must set it to zero. + * - __u8 + - ``data``\ [48] + - The packet payload. See :ref:`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. + +Packets are always passed in ascending line number order, without +duplicate line numbers. The :c:func:`write()` function and +the :ref:`VIDIOC_QBUF` ioctl must return an ``EINVAL`` +error code when applications violate this rule. They must also return an +EINVAL error code when applications pass an incorrect field or line +number, or a combination of ``field``, ``line`` and ``id`` which has not +been negotiated with the :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` or +:ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl. When the line numbers are +unknown the driver must pass the packets in transmitted order. The +driver can insert empty packets with ``id`` set to zero anywhere in the +packet array. + +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. + +A sliced VBI device may support :ref:`read/write <rw>` and/or +streaming (:ref:`memory mapping <mmap>` and/or +:ref:`user pointer <userp>`) I/O. The latter bears the possibility of +synchronizing video and VBI data by using buffer timestamps. + +Sliced VBI Data in MPEG Streams +=============================== + +If a device can produce an MPEG output stream, it may be capable of +providing +:ref:`negotiated sliced VBI services <sliced-vbi-format-negotitation>` +as data embedded in the MPEG stream. Users or applications control this +sliced VBI data insertion with the +:ref:`V4L2_CID_MPEG_STREAM_VBI_FMT <v4l2-mpeg-stream-vbi-fmt>` +control. + +If the driver does not provide the +:ref:`V4L2_CID_MPEG_STREAM_VBI_FMT <v4l2-mpeg-stream-vbi-fmt>` +control, or only allows that control to be set to +:ref:`V4L2_MPEG_STREAM_VBI_FMT_NONE <v4l2-mpeg-stream-vbi-fmt>`, +then the device cannot embed sliced VBI data in the MPEG stream. + +The +:ref:`V4L2_CID_MPEG_STREAM_VBI_FMT <v4l2-mpeg-stream-vbi-fmt>` +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. + +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. + +The following subsections specify the format of the embedded sliced VBI +data. + +MPEG Stream Embedded, Sliced VBI Data Format: NONE +-------------------------------------------------- + +The +:ref:`V4L2_MPEG_STREAM_VBI_FMT_NONE <v4l2-mpeg-stream-vbi-fmt>` +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. + +MPEG Stream Embedded, Sliced VBI Data Format: IVTV +-------------------------------------------------- + +The +:ref:`V4L2_MPEG_STREAM_VBI_FMT_IVTV <v4l2-mpeg-stream-vbi-fmt>` +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 *Private +Stream 1 PES* packet encapsulated in an MPEG-2 *Program Pack* in the +MPEG stream. + +*Historical context*: This format specification originates from a +custom, embedded, sliced VBI data format used by the ``ivtv`` driver. +This format has already been informally specified in the kernel sources +in the file ``Documentation/userspace-api/media/drivers/cx2341x-uapi.rst`` . 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. + +This format's use is *not* exclusive to the ``ivtv`` driver *nor* +exclusive to CX2341x devices, as the sliced VBI data packet insertion +into the MPEG stream is implemented in driver software. At least the +``cx18`` driver provides sliced VBI data insertion into an MPEG-2 PS in +this format as well. + +The following definitions specify the payload of the MPEG-2 *Private +Stream 1 PES* packets that contain sliced VBI data when +:ref:`V4L2_MPEG_STREAM_VBI_FMT_IVTV <v4l2-mpeg-stream-vbi-fmt>` +is set. (The MPEG-2 *Private Stream 1 PES* packet header and +encapsulating MPEG-2 *Program Pack* header are not detailed here. Please +refer to the MPEG-2 specifications for details on those packet headers.) + +The payload of the MPEG-2 *Private Stream 1 PES* packets that contain +sliced VBI data is specified by struct +:c:type:`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). + +.. c:type:: v4l2_mpeg_vbi_fmt_ivtv + +struct v4l2_mpeg_vbi_fmt_ivtv +----------------------------- + +.. tabularcolumns:: |p{1.0cm}|p{3.8cm}|p{1.0cm}|p{11.2cm}| + +.. flat-table:: + :header-rows: 0 + :stub-columns: 0 + :widths: 1 1 2 + + * - __u8 + - ``magic``\ [4] + - A "magic" constant from :ref:`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, ``itv0`` or + ``ITV0``, to use for the payload data. + * - union { + - (anonymous) + * - struct :c:type:`v4l2_mpeg_vbi_itv0` + - ``itv0`` + - 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. + * - struct :ref:`v4l2_mpeg_vbi_ITV0 <v4l2-mpeg-vbi-itv0-1>` + - ``ITV0`` + - 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. + * - } + - + +.. _v4l2-mpeg-vbi-fmt-ivtv-magic: + +Magic Constants for struct v4l2_mpeg_vbi_fmt_ivtv magic field +------------------------------------------------------------- + +.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}| + +.. flat-table:: + :header-rows: 1 + :stub-columns: 0 + :widths: 3 1 4 + + * - Defined Symbol + - Value + - Description + * - ``V4L2_MPEG_VBI_IVTV_MAGIC0`` + - "itv0" + - Indicates the ``itv0`` member of the union in struct + :c:type:`v4l2_mpeg_vbi_fmt_ivtv` is + valid. + * - ``V4L2_MPEG_VBI_IVTV_MAGIC1`` + - "ITV0" + - Indicates the ``ITV0`` member of the union in struct + :c:type:`v4l2_mpeg_vbi_fmt_ivtv` is + valid and that 36 lines of sliced VBI data are present. + + +.. c:type:: v4l2_mpeg_vbi_itv0 + +.. c:type:: v4l2_mpeg_vbi_ITV0 + +structs v4l2_mpeg_vbi_itv0 and v4l2_mpeg_vbi_ITV0 +------------------------------------------------- + +.. tabularcolumns:: |p{5.2cm}|p{2.4cm}|p{9.9cm}| + +.. flat-table:: + :header-rows: 0 + :stub-columns: 0 + :widths: 1 1 2 + + * - __le32 + - ``linemask``\ [2] + - Bitmasks indicating the VBI service lines present. These + ``linemask`` values are stored in little endian byte order in the + MPEG stream. Some reference ``linemask`` bit positions with their + corresponding VBI line number and video field are given below. + b\ :sub:`0` indicates the least significant bit of a ``linemask`` + value: + + + :: + + linemask[0] b0: line 6 first field + linemask[0] b17: line 23 first field + linemask[0] b18: line 6 second field + linemask[0] b31: line 19 second field + linemask[1] b0: line 20 second field + linemask[1] b3: line 23 second field + linemask[1] b4-b31: unused and set to 0 + * - struct + :c:type:`v4l2_mpeg_vbi_itv0_line` + - ``line``\ [35] + - 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 ``linemask`` array, starting from b\ :sub:`0` + of ``linemask``\ [0] up through b\ :sub:`31` of ``linemask``\ [0], + and from b\ :sub:`0` of ``linemask``\ [1] up through b\ :sub:`3` of + ``linemask``\ [1]. ``line``\ [0] corresponds to the first bit + found set in the ``linemask`` array, ``line``\ [1] corresponds to + the second bit found set in the ``linemask`` array, etc. If no + ``linemask`` array bits are set, then ``line``\ [0] may contain + one line of unspecified data that should be ignored by + applications. + + +.. _v4l2-mpeg-vbi-itv0-1: + +struct v4l2_mpeg_vbi_ITV0 +------------------------- + +.. tabularcolumns:: |p{5.2cm}|p{2.4cm}|p{9.9cm}| + +.. flat-table:: + :header-rows: 0 + :stub-columns: 0 + :widths: 1 1 2 + + * - struct + :c:type:`v4l2_mpeg_vbi_itv0_line` + - ``line``\ [36] + - A fixed length array of 36 lines of sliced VBI data. ``line``\ [0] + through ``line``\ [17] correspond to lines 6 through 23 of the + first field. ``line``\ [18] through ``line``\ [35] corresponds to + lines 6 through 23 of the second field. + + +.. c:type:: v4l2_mpeg_vbi_itv0_line + +struct v4l2_mpeg_vbi_itv0_line +------------------------------ + +.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}| + +.. flat-table:: + :header-rows: 0 + :stub-columns: 0 + :widths: 1 1 2 + + * - __u8 + - ``id`` + - A line identifier value from + :ref:`ITV0-Line-Identifier-Constants` that indicates the type of + sliced VBI data stored on this line. + * - __u8 + - ``data``\ [42] + - The sliced VBI data for the line. + + +.. _ITV0-Line-Identifier-Constants: + +Line Identifiers for struct v4l2_mpeg_vbi_itv0_line id field +------------------------------------------------------------ + +.. tabularcolumns:: |p{7.0cm}|p{1.8cm}|p{8.7cm}| + +.. flat-table:: + :header-rows: 1 + :stub-columns: 0 + :widths: 3 1 4 + + * - Defined Symbol + - Value + - Description + * - ``V4L2_MPEG_VBI_IVTV_TELETEXT_B`` + - 1 + - Refer to :ref:`Sliced VBI services <vbi-services2>` for a + description of the line payload. + * - ``V4L2_MPEG_VBI_IVTV_CAPTION_525`` + - 4 + - Refer to :ref:`Sliced VBI services <vbi-services2>` for a + description of the line payload. + * - ``V4L2_MPEG_VBI_IVTV_WSS_625`` + - 5 + - Refer to :ref:`Sliced VBI services <vbi-services2>` for a + description of the line payload. + * - ``V4L2_MPEG_VBI_IVTV_VPS`` + - 7 + - Refer to :ref:`Sliced VBI services <vbi-services2>` for a + description of the line payload. + + +.. [#f1] + According to :ref:`ETS 300 706 <ets300706>` lines 6-22 of the first + field and lines 5-22 of the second field may carry Teletext data. + +.. [#f2] + See also :ref:`vbi-525` and :ref:`vbi-625`. |