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Description  |
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This invention relates to a television transmission system comprising a
transmitter station and one or more receivers. The invention relates more
particularly to such a television transmission system which is adapted for
video recorder programming using teletext data.
The programming of a domestic video recorder is normally carried out
manually by a user operating a combination of a plurality of programme
keys which are provided on a control panel. The programming involves the
selection of a television channel, the selection of a date, the selection
of a start recording time, and the selection of a stop recording time (or
a record time period).
It has been proposed in West Germany to use an existing teletext service,
known as Videotext, to transmit programming information which can be used
to programme a video recorder automatically to record a future programme
following selection of that programme by a user. The facility providing
this programming information is called "Videotext Programmed
Videorecorder" (VPV).
European Patent Specification No. 0 191 149 (A1) relates to this automatic
programming of a video recorder. This patent specification refers to
Videotext as an information service in which data blocks are transmitted
in specific lines in the field blanking interval of a television signal.
The actual teletext system which this Videotext information service uses
conforms essentially to that described in the document "Broadcast Teletext
Specification", September 1976, published jointly by the British
Broadcasting Corporation, Independent Broadcasting Authority and British
Radio Equipment Manufacturers' Association.
One facility of the Videotext information service is the provision of
programme schedules which are displayed as teletext pages and given
details of the programmes and programming timings in at least the
television channel which is used by the transmission source that provides
the Videotext information service.
It is known in the art that the transmitted teletext pages used for the
Videotext information service comprise up to 24 data rows each of which
can contain teletext display data, teletext non-display data, or a
combination of both. Each data row comprises 40 character bytes. This
format conforms to the aforementioned document "Broadcast Teletext
Specification". A teletext page which includes teletext non-display data
as programming information for the (VPV) facility is restricted in the
amount of teletext data which can be used for displaying the programme
details with which this facility is associated. This results in an
editorial restriction of the layout of the teletext pages for displaying
the programme schedules. This editorial restriction is further exacerbated
by the inherent limitation of the teletext format used, which requires the
teletext data for the programming information to be in the same data row
as the teletext data for the associated displayed programme details.
It is an object of the present invention to lessen substantially such
editorial restriction by providing an improved means for using teletext
data for transmitting video recorder programming information.
According to the invention, a television transmission system comprising, a
transmitter station including teletext data transmitting means, and at
least one television receiver having interconnected therewith a video
recorder, and wherein said teletext data transmitting means is arranged to
transmit teletext pages containing both teletext display data representing
displayable programme details and teletext non-display data representing
programming information which is associated with the programme details and
which can be used for video recorder programming; is characterised in tat
said teletext non-display data is in addition to and does not replace
possible teletext display data and that said teletext non-display data is
contained in at least one extension packet which is in addition to data
packets of a teletext page which can contain teletext display data.
A television transmission system according to the invention affords the
advantage that because the programming information is not transmitted in
those data packets of a teletext data which can contain teletext display
data, these data packets may be utilised fully for transmitting displayed
programme details.
The invention also comprises said teletext data transmitting means per se,
when arranged to transmit in one or more extension packets of a teletext
page containing data packets representing displayable programme details,
teletext non-display data representing associated video recorder
programming information.
In carrying the invention into effect a video recorder may be equipped with
its own teletext decoder, as well as the normal television signal
receiving circuits. Alternatively, a television receiver provided with a
teletext decoder could be provided with a suitable control interface to a
video recorder. In either case, a user would select teletext in
conventional fashion and choose teletext pages giving details of
television programmes.
The control arrangement within the teletext decoder would be such that on
deciding to record a particular programme, a user causes a cursor to
appear on the television screen by pressing a cursor button on a remote
control unit. Further pressing of this button causes the cursor to move
automatically to each next programme displayed on the page, until it
reaches the desired programme. Subsequent pressing of a `record this`
button loads the corresponding information (programme source, date, time
label) into the video recorder programming circuits automatically. The
programming information is invisible to the user, who simply chooses the
programme from the schedule presented on the screen.
European Patent Specification No. 0 191 149 (A1) also refers to another
facility used in the existing television service in West Germany of
labelling transmitted television programmes with identification
information which gives "real-time" indications of programme "start" and
"finish" times. This facility is called "Video Programme Service" (VPS)
and reference is made in this European patent specification of the
possibility of including this identification information as further
teletext non-display data.
An important subsidiary feature of the present invention consists in the
transmission by the teletext data transmitting means of such further
teletext non-display data representing identification information in
further extension packets whose contents a teletext decoder is adapted to
receive, store and process without any page selection being effected. It
is mentioned that the use of such further extension packets for
transmitting other control information and the organisation of a teletext
decoder to receive these extension packets without specific page selection
being necessary, is already known in the art.
With this subsidiary feature provided, the VCR programming circuits of a
video recorder look for broadcast identification information matching the
previously downloaded programming information, and when there is a match
(not necessarily at the previously intended time) the recording process is
set in motion. In this way the selected programme is recorded on tape in a
simple and efficient manner. The detailed methods of control would be a
matter for individual video recorder manufacturers.
In order that the invention may be more fully understood reference will now
be made by way of example to the accompanying drawings, of which:
FIG. 1 shows diagrammatically the functions which are necessary for
automatic video recorder programming in accordance with the invention;
FIG. 2 shows a possible technique for coding video recorder programming
information in the performance of the invention; and
FIG. 3 shows diagrammatically a video recorder with its own teletext
decoder for use in a system according to the invention.
In the performance of the invention, three considerations are important for
the coding of the video recorder programming information which is
transmitted within the teletext coding structure. Firstly, the way in
which teletext pages are selected to ease a user's task, considering that
several programmes may be chosen for days or even weeks ahead. This
inevitably means a substantial number of teletext pages. Secondly,
information must be coded for a given page to indicate the positions on a
television screen appropriate for the cursor, and to associate with each
cursor position control data relevant to the corresponding programme.
Finally, the transmission of programme identification information at the
time programmes are broadcast must be considered.
The necessary functions for these considerations are summarised in FIG. 1
of the accompanying drawings. The first function "Selecting the Page" can
be effected using the normal FLOF/Fastext system (see `User Friendly Page
Access (FLOF) Code of Practice`, which is an Appendix to the World System
Teletext Technical Specification published by the Department of Trade and
Industry). No extra facilities are needed. The use of the sub-code page
linking feature to `freeze` rotating pages may be appropriate in many
cases.
For the second function "Selecting the Item", the display of a programme
schedule on a teletext page can be done with full editorial freedom. For
example, a page giving programmes some days ahead might control a simple
list of perhaps 16 programmes with titles and starting times. Conversely,
a page might refer to just one programme, e.g. a film, with detailed
background information. Normal page coding (including the status row for
FLOF prompts) applies to the displayed information.
The editor has to decide how many titles of recordable programmes there are
on the page, and allocate to each one a location on the screen (row and
column) where it would be reasonable to place a cursor to refer to the
title. The cursor position should precede the programme title on the same
row, to allow it to be used for reference.
For the third function "Recording the Item", programming information for
the associated programme is allocated to each designated cursor position,
programme source, date and nominal starting time. All this information is
coded into extension packet 26 using previously unallocated code
combinations. This technique allows commonality of decoder hardware and
software, as most future teletext decoders will also use packet 26 to
obtain an extended language capability. Subsequently, when a "real-time"
programme label transmitted in extension packet 26 corresponds to the
stored programming information, the video recorder is rendered operable to
record the associated programme which is then being transmitted.
A coding technique using an extension packet 26 is shown in FIG. 2. This
packet 26 comprises the usual clock run-in bits RI, a framing code FC, a
packet number 26 and a packet 26 sub-code number 0. Four types of packet
26 groups (`triplets`) are used to define programming information. They
are, respectively, Source Definition, Date Definition, Hours Definition
and Minutes Definition. Each "triplet" comprises 18 useful data bits of
which 6 are address bits, 5 are mode bits and are data bits.
It is envisaged that the packet groups defining programming information
would follow in the transmission order the transmission of any packet
groups used for display or character set enhancement. All the programming
information would be together and not interleaved with other functions. On
completion of the programming information the normal termination rules
would apply.
In general, a teletext page will contain programme titles for programmes
from only one source on one date. The Source Definition and Date
Definition groups should be transmitted first, but only one transmission
per page is required. In contrast, a pair of Hours Definition and Minutes
Definition groups must be transmitted for each programme title displayed.
These pairs should be transmitted in the order of the cursor positions to
which they refer (left to right and top to bottom).
If the Source or Date of a programme is different from its predecessor, a
Source Definition or Date Definition group must be inserted as appropriate
before the corresponding pair of Hours Definition and Minutes Definition
groups. For each displayed programme title, the decoder uses the latest
defined Source or Date values.
The Source Definition group is a packet 26 row address group with the mode
description code set to 0100. It defines the source of the programme to
which it refers, the country of origin and the transmitter network. The
coding of this group does not address any particular location on the
display, but is associated with a cursor location by virtue of its
position in the transmission sequence as indicated above. Address values
(decimal) of 48 to 63 define country of origin. The two most significant
address bits define the country of origin. Data bits 1 to 6 define the
programme source. Different programme source codes may apply to the same
television channel at the receiver, for example to distinguish between
national and regional programmes. The broadcaster should label local
programme variations with the correct local source code, so that no
ambiguity in recording can arise. It is up to each receiver to indicate to
the user whether it is capable of receiving programmes from a particular
source. Data bit 7 defines the address field, 0 giving the first address
field and 1 the second address field. Effectively, this allows up to 128
programme sources to be defined per country.
The date definition group is a packet 26 row address group with the mode
description code set to 01001. It defines the calendar date of the
programme to which it refers. The coding of this group does not address
any particular location on the display, but it is associated with a cursor
location by virtue of its position in the transmission sequence as
indicated above. Address values (decimal) of 49-60 define the month, 49
being January and 60 being December. Data bits 1 to 4 define the units
digit of the day, in binary coded decimal form, with bit 1 the least
significant bit. Data bits 5 and 6 define the tens digit of the day, with
bit 5 the least significant bit. Data bit 7 is normally 0 to signify the
programming function. When data bit 7 is set to 1 the data is reserved for
future applications and should be ignored by the programming until the
next Date Definition Group with bit 7 set to 0.
The Hours Definition group is a packet 26 row address group with the mode
description code set to 01010. It defines the `hours` element of the
programme starting time, and is always the first of a pair of Hours and
Minutes Definition groups. Address values (decimal) of 40-63 define the
row address of the cursor position required. Values 41-63 define rows 1 to
23 and value 40 defines row 24 in conventional fashion. A cursor cannot be
located in the page header, row 0. Data bits 1 to 4 define units digit of
the hour, in binary coded decimal form, with bit 1 the least significant
bit. Data bits 5 and 6 define the tens digit of the hour, with bit 5 the
least significant bit. Data bit 7 is normally set to 0, but may be set to
1 to indicate a restricted condition. This allows the decoding equipment
to generate a suitable status message or control if required.
The Minutes Definition group is a packet 26 character space address group
with the mode description code set to 00110. It defines the `minutes`
element of the programme starting time, and is always the second of a pair
of Hours and Minutes Definition groups. Address values (decimal) of 0 to
39 define the column address of the cursor position required, in
conventional fashion. Data bits 1 to 4 define the units digit of the
minute, in binary coded decimal form, with bit 1 the least significant
bit. Data bits 5 to 7 define the tens digit of the minute, with bit 5 the
least significant bit.
There is also an Hours Finish group which is a packet 26 row address group
with the mode description code set to 01011. It is used in the same way as
the Hours Definition group, in a pair with a Minutes Definition group, but
defines the finishing time of the preceding programme referred to on the
page. Display of the finishing time is optional at the editor's
discretion. The finish pair allows the equipment to calculate the amount
of tape required to record the last item on a page. It should also be used
within a page where the finishing time of a programme is different from
the starting time of the next programme.
The assignment of programming information to a teletext page requires the
transmission of additional information in packet 26, as indicated above.
However, the overhead is quite small, and each page only requires
sufficient packets 26 to deal with the number of programmes decided by the
editor. Assuming a page refers to only one source on one date 5+2N
triplets are required where N is the number of programmes. Each packet 26
contains thirteen triplets; the capacity of the technique is tabulated
below.
______________________________________
No. of Transmission
No. of packets
programmes overhead
______________________________________
1 4 4%
2 10 8%
3 17 11%
4 23 15%
5 30 19%
6 36 23%
______________________________________
With present editorial techniques a typical programme schedule page
contains less the 17 programme titles. This could have programming
information assigned in 3 packets 26 with a transmission overhead of
approximately 11%. As the pages would probably be a small proportion of a
teletext service, the overall transmission overhead (in terms of increased
access time or reduced number of pages) is small.
The programme labels at the time of transmission are sent in packet 8/30
format 2. (See section 13.3 of the WST specification).
Packet 8/30/2 should be transmitted once per second, interleaved with the
normal packet 8/30/0 for FLOF purposes. The initial page and status
message fields of packets 8/30/0 and 8/30/2 should be identical. A delay
of at least 100ms should elapse between transmissions of the two types of
packet 8/30. These constraints permit the use of slow (cheap) decoder
software and allow a faster presentation of status messages while scanning
through channels.
In order to allow sufficient time for reliable reception of the signal and
the starting time of the recorder mechanics, the programme label should be
transmitted 10 seconds in advance of the corresponding programmes.
The system allows simplified programming as described when used with a
video recorder having full facilities including a teletext decoder.
However, it is also envisaged that there will be a significant number of
simple video recorders in the field. These will not include a full
teletext decoder for reasons of cost, but will be capable of receiving the
programme labels in packet 8/30/2.
As a result, these simple machines are capable of dealing with programme
schedule alterations, but still have to be programmed by the user in
conventional fashion. Consequently the programme labels used must be
compatible with normal time schedules, particularly as some broadcasters
may not provide a programming service, when the video recorder must revert
to using a conventional timer.
The programme labels should be normally in local time at the originating
centre. The same local time should be used in the teletext programme
schedule page. If the programme schedule is altered, the original label
corresponding to the first published starting time must be maintained. In
this case, a revised teletext schedule should show the new starting time,
but also needs to display the original label for the benefit of owners of
manually programmed video recorders. The editor should clearly identify
the label for such a programme, perhaps using a different colour in a
standard way. Similar indication of a different label should be published
in any medium giving programme schedules, for example a newpaper.
If programme schedule information is published in a different time zone
from the programme source, it is necessary to indicate labels for every
programme item. This gives the user of a manually programmed video
recorder the correct programming data, which is no longer local time at
the receiver.
Under normal circumstances (no programming alterations and receiver in the
same time zone as the transmitter) labels and local times are identical
and there is no need for separate indication of programming information.
The video recorder represented by the diagram shown in FIG. 3 is provided
with its own teletext decoder for the performance of the invention. This
video recorder comprises an aerial input 1 for receiving UHF television
signals from a transmitting station (not shown). The received television
signals are applied to a tuner stage 2 which is tunable to different
television channels by a tuning control circuit 3. The output signal from
the tuner stage 2 is applied to an intermediate frequency stage 4 whose
output signal is in turn applied to a demodulator stage 5.
The output signal from the demodulator 5 is a composite video signal which
is applied to video record/play stage 6 and also to a teletext decoder 7.
The operation of the video record/play stage 6 is under the control of a
record/play control circuit 8. The operations of the two control circuits
3 and 8 and of the teletext decoder are determined by a microcontroller 9
over a data bus 10. A remote control stage comprising an infra-red
receiver 11 and a user-controlled hand-held module 12 with a keypad and an
infra-red transmitter transmit user select signals to the microcontroller
9. There are also connected to the data bus 10 a timer stage 13 which
provides a combined clock/calender for the video recorder, a non-volatile
memory 14 in which channel tuning data for the tuning control circuit 3 is
stored, and a non-volatile memory 15 in which programming and control data
for the various record and play functions of the video recorder are
stored.
The record/play stage 6 produces a composite video signal CV on playback.
This signal CV is applied via a UHF modulator stage 16 which
re-establishes a UHF television signal which is applied via a multiplex
stage 17 to an output terminal 18 of the video recorder The received UHF
television signal at the aerial input 1 is also applied directly via the
multiplex stage 17 to the output terminal 18.
The teletext decoder 7 comprises a video processor 19, a data acquisition
circuit 20 and a page memory 21. The video processor 7 receives the
composite video signal CV from the demodulator stage 5 and produces data
pulses DP and clock pulses CP from the teletext data contained in the
signal CV. The data pulses relating to required teletext pages are
acquired selectively by the data acquisition circuit 20 and stored in the
page memory 21. When stored data is read out from the teletext decoder for
utilisation, it is in the form of RGB signals which are colour encoded by
an encoder stage 22 to restitute a composite video signal CV'. This signal
CV' is applied to the modulator stage 16 to re-establish a UHF television
signal for a teletext display page. The signal CV' may also be applied to
the record/play stage 6 for recording, for instance when it represents
sub-titles.
In the performance of the invention the microcontroller 9 performs the
following functions:
(i) The control of the teletext decoder for receiving and displaying
requested programme pages, together with the programming information in
packet 26.
(ii) The cursor movement on a displayed programme page.
(iii) The extraction of programming information from a page stored in the
page memory and the re-storage of this programming information in the
memory 15.
(iv) The comparison of the stored programming information with the
programme identification information transmitted in "real-time" in the
further extension packets 8/30/2.
From reading the present disclosure, other modifications will be apparent
to persons skilled in the art. Such modifications may involve other
features which are already known per se and which may be used instead of
or in addition to features already described herein. Although claims have
been formulated in this application to particular combinations of
features, it should be understood that the scope of the disclosure of the
present application also includes any novel feature or any novel
combination of features disclosed herein either explicitly or implicitly
or any generalisation or modification thereof which would be apparent to
persons skilled in the art, whether or not it relates to the same
invention as presently claimed in any claim and whether or not it
mitigates any or all of the same technical problems as does the present
invention. The applicants hereby reserve the right to formulate new claims
to such features and/or combinations of such features during the
prosecution of the present application or of any further application
derived thereform.
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