BBC R&D ANNUAL REVIEW

Transcription

1 technical architecture audio description for digital television capacity planning digital text, enhanced tv and interactive platforms schedule interface widescreen television BBC R&D ANNUAL REVIEW 35

2 GLASGOW Newcastleupon-Tyne BELFAST MANCHESTER Leeds Nottingham BIRMINGHAM The BBC is a large organisation. To fulfil our obligations, we have many national, regional and local studios, broadcasting through a wide variety of analogue and digital outlets. How can we deliver this diversity in a manner which is flexible, efficient, and which offers a common brand image, whichever delivery mechanism is chosen? The Systems Architecture the interconnection of all the playout facilities, multiplexers and delivery platforms is a key technical component in this challenge. CARDIFF Cambridge Norwich The BBC launched its digital television services on digital satellite in October 1998, closely followed on the digital terrestrial television (DTT) platform in November SInce then we have been working to provide additional services and enhancements, and to prepare for the rollout of services on digital cable and the emerging Broadband/DSL platforms. BBC R&D is responsible for the design of the technical architecture for BBC Public Service Digital Television services in the UK. During 1999, the BBC launched several new BBC digital services, such as BBC Knowledge, and added radio to its satellite television multiplex. As a consequence, we have reviewed and, where necessary, modified the technical architectures needed for coding, multiplexing and distribution to support these new services. Plymouth BRISTOL TELEVISION CENTRE Southampton Key: DTT/DSAT primary distribution Path 1 Path 2 DSAT secondary distribution and regional sustaining feeds Path 1 Path 2 Multidrop connections BBC R&D ANNUAL REVIEW APRIL 1999 MARCH 2000

3 We have had to ensure that the BBC uses its available capacity to maximum efficiency on all delivery Each platform delivers Digital Text in a different way. Subtitles are processed and the different picture aspect ratio. Compression coders for STATISTICAL MULTIPLEXING ON DSAT Radio on the satellite transponder The BBC s second transponder carries services multiplex and a complete English multiplex. The latter includes specially commissioned news platforms, so as to accommodate these differently on the terrestial and regional contributions For digital satellite, the regional services a mix of the National versions of programmes containing items from all new services without jeopardising satellite systems. would be installed locally. are returned to London, where they BBC ONE and BBC CHOICE, all regions. Services in these feeds are picture quality. THE CHALLENGES OF PLATFORM NEUTRALITY THE TECHNICAL ARCHITECTURE The BBC is both a regional and a At launch, common coding at constant bit rate was chosen for both satellite and terrestrial delivery. are combined with the London material to form the two transponder feeds. This combination is essentially an add-drop transport-stream multiplex. currently with constant bit-rate video coding. However, here too changes have been made to the multiplex during the past year to accommodate eleven coded at the final emission rates, to avoid further decode/recode operations and to minimise the bit rate required for distribution. The UK-wide services The BBC aims to make its digital national broadcaster. There are Now, separate coding for statistical There is no other processing of the BBC radio services (BBC Radios 1, 2, 3, 4 are those with no regional variations television services available to the substantial differences in programming multiplexing has now been introduced regional contributions except for the (FM and LW versions), Radio 5 Live, (for example BBC NEWS 24), and these licence fee payer on all of the between England and Scotland, Wales, on one of the satellite-delivered conditional access encryption applied BBC Radios Scotland Wales and Ulster, are combined in the studio centres in available delivery platforms, and Northern Ireland the Nations. multiplexes to accommodate an extra to all the satellite services to ensure BBC World Service and BBC Radio Scotland, Wales and Northern Ireland, terrestrial, satellite, cable and the Within England there are also lesser service BBC Knowledge a good correct geographical access to Asian Network). These are now all with their respective national regional emerging broadband/dsl systems. variations between London and the ten example of how the system services in accordance with available across the UK. Indeed, since programming to provide a regional The challenge is to offer viewers other English regions. architecture has had to adapt to meet programme-rights restrictions. all but Radio 5 Live are broadcast multiplex for each Nation. the same service propositions, with the We have tried to maintain this evolving requirements. The BBC uses two whole unencrypted, they can now be received At the launch, it was not possible to same look and feel, whichever regional editorial structure as far as The distribution architecture is transponders on the Astra 2A satellite. throughout most of Europe on any provide regional programming when platform the individual viewer uses. possible in the digital world. To do so based on ATM point to multi-point The English Region versions of DVB-compliant satellite receiver. available in the English Regions the There are large differences in the data has required a rather ambitious and point to point connections, BBC ONE, BBC TWO, BBC CHOICE Introduction of these radio services necessary equipment was not available capacities available to the BBC on each architecture for the connection of all carrying MPEG-2 single and and BBC News 24 originating in London required new contribution feeds to be from the manufacturers and there was of the platforms and the respective our sites. Whilst the network for multi-programme transport streams. are statistically multiplexed along with arranged from the national and regional simply too much else to do. Until gateway keepers have chosen different distributing our analogue television has The UK-wide and London-based the new BBC Knowledge service and centres where they originate. Most of recently, the English multiplex has been technical standards on the different been developed gradually over many services are coded in London for broadcast on one transponder. the new audio compression coding passed straight through at the English platforms for various services and years, the rapid development of new emission using a video bit rate of just Statistical multiplexing was equipment is sited at Broadcasting House. regional studios so that all terrestrial service components. For example: services for digital delivery by satellite, over 5 Mbit/s. Regional services are introduced on DSAT during the summer A circuit to Television Centre delivers viewers throughout England have A terrestial multiplex can terrestrial and cable has required a created locally, using sustaining feeds of It has enabled six services to the encoded radio signals, where they received the same programming with support a data rate of just over fresh approach. from London as a basis. The sustaining be conveyed within the capacity are multiplexed with the digital TV no regional variations. 24 Mbit/s, whereas a satellite Given the short time scales for feeds are coded at a higher coding rate originally required for five services programme services for transmission. Nevertheless, we created the transponder, can carry implementation, the availability (or lack of 8.7 Mbit/s, which gives a margin for coded at constant bit-rate, allowing original architecture with the necessary approximately 33.8 Mbit/s. This of) commercial equipment at the time, the subsequent decode/recode BBC Knowledge to be broadcast on the Providing English regional interfaces to allow English Regionality difference in capacity on the and the need for economy, three operation. It offers an acceptable satellite platform without the need to programming on to be implemented in stages after the two platforms, along with the key decisions were taken for the compromise between quality and bit acquire additional expensive terrestrial transmissions initial launch. When English regional requirement to support national initial installations. rate. The National centres at Glasgow, transponder capacity. It required the Our aim has always been to offer in opt-outs are available, these are coded and regional variants of some The digital services would be Cardiff and Belfast also have individual modifications to the architecture for the the digital world the same geographical locally and inserted in the incoming services, means that it is not distributed independently of connections from London over which new coding and multiplexing equipment availability of all National and English sustaining multiplex, replacing possible to broadcast exactly the the analogue programmes, clean programme material without to be evaluated, installed and tested at English regional television services that the corresponding services sourced same multiplex of services or to avoid PAL coding picture regional branding or interstitial material Television Centre in time for the launch BBC viewers have enjoyed in the from London. The sustaining feed of video coding rates on the artefacts and to take account can be transferred to a local server of BBC Knowledge. analogue domain. the complete English multiplex is different platforms. The systems of presentational differences for delayed transmission. To facilitate this, two sustaining retained, as this allows a service architecture has to reflect this. feeds are provided, the UK-wide APRIL 1999 MARCH 2000 BBC R&D ANNUAL REVIEW

4 The architecture regional connections. National region sustaining feeds DSAT contribution London sustaining feeds to be maintained albeit without local direct from coders at Television Centre, programming, coding and primary English region programme inserts in the case of a failure in the regional equipment. and have implemented a dedicated link between Television Centre and their multiplexing are not necessarily carried out in the same place. This separation During 1999, the equipment head-end operation in Bromley for this of coding and multiplexing makes needed to code and insert the purpose. We are considering offering statistical multiplexing very difficult to regional programmes locally in the the companies a full sustaining implement for the BBC s terrestrial The architecture London. to regions English Regions has become available. As a result of trials in Bristol, multiplex. This would minimise the dependence of cable on the other multiplex. Without it there is insufficient capacity to convey an implementation of the infrastructure delivery platforms, thus minimising additional service such as Knowledge for English Regionality in all our cross-platform change control issues, without severely degrading the picture regional centres is now complete and and making it easier for the cable quality of all the services within the playout suites routeing sustaining feeds MPEG-2 coding and multiplex ATM adaptation three Nations DSAT routeing and multiplex conditional access encryption London region DTT DSAT2 DSAT1 regional terrestrial services are on-air. Rollout of digital cable The three main cable operators (Cable & Wireless, ntl and Telewest) are now starting to roll out digital cable services. Progress is slower than we originally anticipated. We are working with these companies, to ensure that BBC digital companies to take our services. THE LAUNCH OF BBC KNOWLEDGE BBC Knowledge, the BBC s latest new television channel was successfully launched simultaneously on satellite and terrestrial platforms on 1st June Each platform presented its multiplex. Therefore, for the launch of BBC Knowledge, it was necessary to arrange for the service to be broadcast within another operator s multiplex, namely that belonging to SDN. BBC Knowledge is just one of a number of services coded and multiplexed together by SDN, including Channel 5 and a number of other commercial TV UK-wide local TV services are available to licence fee payers on cable, and that the range of own challenges, which were successfully overcome. services. As SDN code all their services at a single location they are able to BBC services and functionality matches On the digital satellite platform, employ statistical multiplexing to that available on the competing satellite BBC Knowledge is carried along with optimise the use of their available data The architecture and terrestrial platforms as closely as other BBC services within a BBC capacity. High-quality video links were Nations. possible. This includes offering viewers multiplex. There isn t enough capacity installed between the BBC Knowledge the correct national or regional version within the multiplex to carry an playout facilities in Television Centre UK-wide DTT services local sources MUX DTT of services for their location. Initially, the cable operators are taking the majority of BBC services additional service using straightforward constant bit rate video coding. Therefore we introduced statistical and SDN s coders and multiplexers, which are located at Langley in Berkshire. BBC R&D designed the off-air from our terrestrial broadcasts, multiplexing. This makes it possible network architecture for delivering the and inserting them into their cable to accommodate six programme BBC Knowledge service to SDN, and regionally opted services ATM adaptation presentation suite code multiplexes. This ensures that the correct regional programming is services within the same total overall bit-rate capacity which prior to the for monitoring the signals. available in different areas. Services launch of BBC Knowledge had national contribution for DSAT decode not available in the terrestrial multiplex have to be obtained from the satellite multiplex and the cable conveyed only five services. It was not practical to use statistical multiplexing on digital terrestrial at companies have adopted different the time BBC Knowledge was launched solutions for this. Cable & Wireless in We said earlier that to retain have chosen to obtain these services the facility for English Regional 40 APRIL 1999 MARCH 2000 BBC R&D ANNUAL REVIEW 41

5 BBC R&D ANNUAL REVIEW There are around one million people in the UK who are sufficiently visually impaired to have difficulty getting the full benefit from the pictures on television. Nevertheless they still tune in: they like the programmes. In radio, we pay special attention to the script to make sure that the listener can create their image of the events being portrayed, but in television we rely on the pictures. This puts partially-sighted people and blind people at a disadvantage. Try just listening to the television one day. You can get a good idea what is happening just from the sound track but there are times when the picture is important. Then, people with impaired vision lose something from the broadcast. For people with impaired vision, audio description is the answer. Audio description provides a commentary which describes the scene to the visually impaired. We leave the main programme sound unchanged, but provide an additional sound component or channel. This is in mono and clean (it has no effects added). During production, the challenge is to combine the commentary with the original programme so that the two provide a complete experience. A well produced programme dramatically improves the experience that blind or partially-sighted people get from their televisions. HOW DO WE DO THAT? The production team creates a clean audio description track, which is broadcast on the DTT network. In the receiver, a special plug-in card removes the audio description, combines it with the normal sound and delivers them to the listener s loudspeakers. We transmit data within the description signal which provides a means of fading the level of the programme sound during description and which provides an optional means of panning the description around the sound stage (e.g. left/centre/right with stereo). programme description fade programme and description time 42 APRIL 1999 MARCH 2000 BBC R&D ANNUAL REVIEW 43

6 video and programme sound UHF programme sound mixed with description AUTHORING normally carries stereo information, but passage being under the control of the There are various editorial issues in we place the description in the left programme maker. output (programme and description mix) audio description. Key events have to be described if they are not clear from the story-line or channel and coded fade and pan data on the right. The studio signal is rugged, easy to use and to monitor, and it survives THE LEGAL FRAMEWORK In 1996, a Broadcasting Act came into force, regulating digital terrestrial programme dialogue. many processes (e.g. synchronisers, television in the UK. The Act states that It is important not to talk over D-A and A-D conversion, rate changing, programme service providers will have the dialogue. Not only does it editing, compression, gain changing etc.). to make at least 10% of their confuse the plot, but some The producer controls the mix of programmes available with audio partially-sighted people may also conventional audio and description. description, by the tenth year of their have hearing difficulties. digital licence. remote control Early experience with audio Coding In addition, the Independent stereo programme sound from receiver description has shown that listeners think it is important to keep the same voice for We have to be economical with our capacity on the DTT multiplex. The audio description signal is coded as Television Commission has stated that the independent programme companies must carry audio description, and have a series. MPEG-1 layer II mono (the same as a quota which increases year on year. A cost-effective prototype authoring used for Digital Radio) at 64 kbit/s. The BBC has made a commitment station for audio description has been The fade and pan information is to at least match the ITC s user control of description volume developed at BBC R&D. It provides facilities to create the audio description, and the support data for the broadcast. embedded with the audio description as user-data (the MPEG-1 specification already provides special facilities for requirements on its public service networks. Today our target is 2% of programmes rising to 4% in the fourth decoded description It generates a file of description and time-codes, plus the fade and pan information and, optionally, a DAT tape such data to be carried, making it a relatively simple process to combine the signals). year of operation. AND THE FUTURE... of the full description track. The gross transport stream bit-rate One of the key issues is how to ensure There may be opportunities to link cost is then 73 kbit/s per described that the special receiver cards are audio description s authoring tools with service. This could be compared available to the target audience. We those used for assisted subtitling. This with the about 260 kbit/s which have developed emulators for the will make it easier to identify gaps in would be needed to transmit a second additional decoder module to help the narrative where there may be stereo mix. develop the market but the small size suitable opportunities for description. of the market, means that it is unlikely decoded main programme sound THE TECHNOLOGY The receiver Audio description requires an additional that a manufacturer will be prepared to develop the equipment without some Distribution within the studio decoder module which is plugged into a form of advance order. The studio signal uses existing common-interface slot in the DTT Third-generation receivers may infrastructure where possible. receiver. The receiver produces a have audio description built in. Until broadcaster s control of mixed volume user s control of mixed volume The description signal and the fade and pan information are conveyed in the studio signal as a stereo signal using separate mix of programme sound and description, with the level of programme sound during a described then, audio description may have a small audience. the well-established AES-3 format. This 44 BBC R&D ANNUAL REVIEW APRIL 1999 MARCH

7 PRESSURE ON CAPACITY understanding of developments in statistical multiplexing (as it is called) from one moment to the next so the Getting the right balance is difficult and a bursty nature. Their bit-rate There is increasing pressure to make contemporary coding technology, uses a reduction in demand on one statistical multiplexer must have a fast requires evaluation across a wide range requirements can vary substantially the most efficient use of available bit- allowing us to evaluate state-of-the-art channel to satisfy an increase in another response time. There will nevertheless of programme material within the from one second to the next, from rate on every platform to allow the commercial coders on behalf of BBC as ( robbing Peter to pay Paul ). Statistical be times when many or all of the statistical multiplex bundle for programme to programme and from BBC to add new service components part of a tender evaluation for statistical multiplexing a group of video coders channels are showing demanding considerable periods of time in order to programme genre to programme genre. (e.g. Audio Description), to expand multiplexing equipment. thus offers the chance of increasing the material. Experience has shown that explore the envelope of possible Sometimes they require high peak existing services (e.g. BBC Text) or to The bit-rate required to code a average quality of a decoded video one evening there may be no occasions combinations. As more of the bit-rates in order to deliver information add new programme services to its given sequence of video to a given signal for a given (average) bit-rate. for which picture quality is significantly population become accustomed to to the viewer in synchronism with the existing digital multiplexes. This quality depends on a wide range of Alternatively it may allow the user to challenged. On the next evening, digital television, viewers will become associated main video and audio question is so important that the BBC factors. These factors include the achieve a picture quality comparable however, the combination of more aware of digital coding artefacts, components for a given service; at has a cross-directorate group activity (detail and movement) within with constant bit-rate coding but at a programme material across the bundle and isolated occurrences of poor other times they are largely inactive, monitoring the use of capacity, and we that sequence. One scene may contain lower average bit-rate. With pressure means there is often insufficient total picture quality may become and their nominal data capacity could have been responsible for maintaining lots of diverse moving details and so be to liberate bit-rate for new services or bit-rate in the bundle to satisfy the conspicuous and disturbing to the be temporarily assigned to other an accurate bit-budget for both digital difficult to code and thus require more service components, the emphasis has demands of the individual channels. public. Hence, further experiments are services or service components. For satellite and terrestrial services, than average bit-rate. The next, been on using statistical multiplexing to When this happens picture quality can planned during 2000 to balance bit-rate, example, the momentarily spare identifying and where possible however, may be easier to code and reduce the average bit-rate be impaired on all demanding channels. perceived quality and BBC programme capacity could be temporarily added to implementing opportunities for bit-rate require less. requirements per service. The BBC runs reactive independent propositions. We will also continue to the bit-rate pool for video coding or savings. We also model the consequences of new programme STATISTICAL MULTIPLEXING Our goal is to determine the point of balance between average bit-rate in a channels for its public services. It is impossible to guarantee schedules and evaluate new commercial tools designed to provide a mechanistic used to convey background data services that are not so time critical. propositions and their practicability Coding video to a constant bit-rate given statistical multiplex bundle and bit rates. There are also notable times measure of quality, and aim to cross The bit rates we are considering are within (and without) the existing tends to be rather inefficient, as the bit- acceptable picture quality. This we when several channels can be showing correlate such measurements with much lower than those for video, so digital infrastructure. rate chosen has to provide the desired have been doing firstly using an offline similar challenging material subjective assessments of the quality. statistical multiplexing of these For a television service the video quality for the worst case (high activity) coding and multiplexing system installed (e.g. Wimbledon and Olympic sports This will help the BBC deliver a additional services will not free component takes the greatest share of scenes. For all less-demanding in Television Centre (on loan from a coverage). These two factors lead satisfactory balance of choice and sufficient bit-rate to accommodate an the service bit-rate so efficiency savings sequences the constant bit-rate is more major manufacturer) and secondly by to high demands on the capacity of quality programmes to our viewers. entire new channel. Nevertheless, there often focus on video coding. The basic coding quality that can be achieved at than sufficient. Nevertheless, there may be practical reasons for using constant running an experiment live on one of the BBC s DSAT transponders. the multiplex. The BBC s expert viewers have, on OTHER SERVICES will be many possibilities for using such opportunistic data multiplexing particular bit-rates is of key importance. bit-rates in a multiplex. In principle, the more channels that occasions, considered that the balance There are other services we provide techniques to make more efficient use The techniques and commercial Across a number of video channels are included in the bit-rate sharing of picture quality has been which may contribute to more efficient of our available bit-rate capacity. compromises applied to video coding the ebb and flow of demand is usually bundle the less likely that all the unacceptable. Public sensitivity to use of the available bit-rate. vary between manufacturers, and are uncorrelated. We can therefore vary channels will demand high bit-rate coding quality on any of the digital Many service components, such as improving with each generation of the allocation of bit-rate to each simultaneously. The demands of a single platforms is largely uncharted and it is DVB-Subtitles and audio description equipment. We maintain an channel rapidly to suit demand. This channel change quickly and dramatically not easy to measure their impressions. (when available for a programme), have 46 APRIL 1999 MARCH 2000 BBC R&D ANNUAL REVIEW 47

8 Data services as part of television are nothing new. For example, the BBC s CEEFAX service started nearly 30 years ago and now regularly attracts 15 million viewers each week. However, this success has created a legacy problem. Most World System Teletext receivers are based an early version of this standard, where the functionality and presentation provided offers for the delivery of improved new exciting services via DTV. THE REALITY OF THE MARKET Teletext standard, taken directly from analogue TV, for its information services. However, the satellite platform is now migrating to a new digital system using OpenTV. In contrast terrestrially, Digital Text was launched using the MHEG standard as agreed with the other terrestrial multiplex operators and service providers. Digital content providers such as the BBC wishing to have a presence on all delivery systems. THE DIGITAL TERRESTRIAL DATA BROADCAST SPECIFICATION The requirement for any new way to analogue Teletext a range of data content is broadcast cyclically, with the opportunity to update, add, or remove content as and when required to reflect changing editorial propositions. MHEG-5 is one of the outputs of the Multimedia and Hypermedia Expert Group. It provides a lightweight (small memory requirements) means of is relatively inflexible. Improving Whilst the launch of DTV has created Cable will use HTML, the internet specification to support an open handling multimedia content, specifying CEEFAX without making existing an opportunity, expectation standard, because it has a direct return receiver market, much like that enjoyed mechanisms for both object receivers obsolete, has proved difficult. management is an important issue. channel which offers exciting interactive by analogue television equipment presentation and user interaction. Of course, digital television (DTV) Receiver processing power is still options. All of these new digital systems manufacturers today, prompted the As one of The Digital Network needs new receiving equipment. This limited compared to a typical provide better presentation formats decision to base it on two international (TDN) members, we took a very active has created a unique opportunity to multimedia-pc and whilst bandwidths than CEEFAX, with improved fonts, (ISO) standards. role in the creation of a UK profile for introduce new platforms for the available may seem large they are still graphics, stills and animations, etc., but The grandly named Digital Storage data services. support of data services. DTV is based around the MPEG-2 standard, which constraining due to the unidirectional nature of the transmission path. they are incompatible with each other. Hence, the challenge is to provide Media Command and Control (DSM-CC) is Part 6 of the MPEG-2 BBC TEXT provides a flexible data delivery Also unlike the encoding of video content creation and playout systems specifications (with Parts 2 and 3, video BBC Text is the BBC s digital text service mechanism. This, coupled with and audio, which are almost always that can support the same Digital Text and audio encoding, being the best that replaces CEEFAX in the world of relatively powerful receivers with based on the ubiquitous MPEG services on these three platforms, known). DSM-CC is an extensive digital television. Digital Text is just the graphics capability, means that powerful standards, commercial and political providing a consistent presentation to toolkit for handling the transfer of first step on the road to fully interactive interactive data services are now pressures have led to a diversity of the viewer, irrespective of their chosen multimedia content from which one TV services, where video, audio and possible. The BBC is keen to exploit implementations across the different delivery platform. part, the Object Carousel, has been data are combined as part of a the opportunities such technology digital delivery systems. Digital satellite This diversity is clearly going to selected to provide a broadcast filing multimedia service proposition, with was launched using the World System create a significant challenge for system. In principle it works in a similar the prospect in the future of a return APRIL 1999 MARCH 2000 BBC R&D ANNUAL REVIEW

9 channel from the viewer to broadcaster Handling the introduction of new development of production tools and testing their prototype receivers. As a the viewer to augment the main video consistent feel to the BBC services for true interactivity. content types, such as images. the functionality of available receivers. result, it is now possible to view and audio components. Like all DTT across the platforms. Due to the differing timetables for rollout on the various delivery The resulting Content Production System (CPS), developed by BBC R&D, PROGRESS TO DATE quarter-screen video of one of our linear services (e.g. BBC ONE, Digital Text services it is based on MHEG-5. However, the digital text Cable operators tend to favour the use of out-of-band delivery of text, platforms, BBC Text was initially went operational in November 1998 in The terrestrial version of BBC Text now BBC TWO, etc.,) within the display of content is synchronised with the exploiting the natural return path of launched terrestrially, although work on time for the initial launch of digital offers (Spring 2000) the digital viewer the Digital Text service. The viewer can playout and transmission of the picture cable systems. This is in contrast to the services for satellite and cable is now terrestrial TV and the BBC s Digital over 800 stories comprising more than now enter and leave the independent and sound of the linear service, allowing embedded data services within the well advanced. Text barker service pages, with thematic navigation BBC Text service directly from/to any additional information to be overlaid at transport streams conveying the Our main requirement was to use Now a new commercially and attractive presentation formats, of the linear services this is known as the appropriate point in the terrestrial and satellite services. This the existing CEEFAX editorial content, developed CPS is being implemented including full colour graphics such as channel association a feature that was programme, if the viewer so wishes. allows the cable user to request which needed to be extracted and with our assistance to support weather maps and still pictures. introduced in March Thus it is possible to add an extra content from remote servers for formatted for re-use with minimum BBC Text services across all delivery Different services can offer their own The first true Enhanced TV service dimension to the delivery of delivery specifically to their set-top human intervention. platforms, whenever possible using the distinctive branding, it is simply a was broadcast by the BBC in June 1999 BBC Knowledge programming. box, in a one-to-one transaction. This had to be accomplished with same core source material. matter of providing the appropriate a special service to accompany the Additional information in the form of Amongst other characteristics, this the minimum of impact on our live Longer-term techniques for truly content, templates and applications. BBC s coverage of the Wimbledon 1999 text and graphics will be available to provides access to a potentially CEEFAX service, in time for an original generic cross-platform content Unlike Teletext, the broadcasters are Lawn Tennis Championships. the viewer for simultaneous display unbounded set of content, in contrast launch date of November 1998, without production and handling are being no longer tied by the technology to Unfortunately, at that time, there were with the video and audio, providing a to the terrestrial and satellite systems, complete technical specifications or investigated as a priority. producing services all looking roughly no suitably equipped receivers in the richer experience. This type of service where the content is constrained by the suitable test receivers. There have been some THE BBC STRATEGY similar there is real opportunity to promote brand image and for the BBC public domain capable of decoding the signals. However, it was still possible could be provided for other channels in the future. characteristics of the carousel. Data services are being introduced interesting issues that have had to The BBC has a generic aim to offer to achieve significant competitive using prototype receivers to give live We developed a new architecture by cable operators as a TV-Internet be considered: where possible its content on all advantage in terms of the service demonstrations off-air to the organisers for this service, ranging from source service comprising content supplied by Mapping CEEFAX pages, delivery systems. This desire applies as propositions, content and functionality and public at Wimbledon to much playout to the delivery of both the selected providers. We have established accessed using a three-digit much to data services as to the main offered to the digital viewer acclaim. This innovative service linear and Digital Text service connection architectures for the number, into a menu-driven, programme services. We have been in A BBC Digital Text service has been provided a wide choice of additional components to SDN on whose provision of BBC content to the various navigable hierarchy. discussion with all the major players on available on-air since the launch of the information, such as player profiles, multiplex BBC Knowledge is broadcast. cable platforms, and we have also Ensuring that text edited using each delivery system. DTT platform back in November latest scores, and a host of other The service went live in April helped to adapt existing content for the CEEFAX fixed-width font However, due to the diversity of However, it was only possible to launch information including an interactive quiz For technical and commercial presentation within the different still renders without over-spill platforms, standards, and the different the BBC Text service publicly a full year (local interaction with the STB), to reasons, the terrestrial platform has led proprietary systems currently operated using the new proportionally implementation timetables, there is a later in November 1999, when suitably supplement the BBC s linear coverage the development and introduction of by the three major cable operators. spaced Tiresias font. (Tiresias phased rollout in progress across the equipped set-top boxes and integrated of the tournament. All of these were the BBC s Digital Text services. BBC TV-Internet services on these has been specifically developed different delivery systems in the order: digital TV receivers were first made accessible simultaneously whilst viewing Nevertheless, we also worked on the platforms are likely to begin during the in consultation with the RNIB to terrestrial, satellite then cable. At the available to the public. quarter-screen video of match coverage systems for satellite and cable services Spring and Summer of aid legibility, especially for the same time the increase in service During the interim period we from one of the BBC s linear digital too. Our aim is to try to use common visually-impaired.) complexity is also being phased as worked closely with our colleagues in TV services. content and applications, but to Suppressing inappropriate visual new service propositions and the BBC to refine and improve the We also developed a new re-author as appropriate for these references, such as See applications are developed and performance of the content and synchronous Digital Text facility to platforms with their different text CEEFAX Page 123. tested. This is supported by our applications, and gave valuable enhance the BBC Knowledge service. standards thereby minimising growing experience in the assistance to the manufacturers by This provides additional information to production costs and effort and giving a APRIL 1999 MARCH 2000 BBC R&D ANNUAL REVIEW

10 terrestrial new platforms satellite BBC internal cable, PA listing BBC Navigator playout broadcasting data service SID is the computer system that we have designed and developed to enable the BBC to create and deliver content to electronic programme guides (EPGs) on digital terrestrial, satellite and Online platforms. presentation planning strategic planning Two principal services are supported: One of the main users of the system in schedules and triggers over various terrestrial and satellite services and to carry 11 radio services on the digital for the various platforms now delivering The creation and delivery of the BBC is the unit which is responsible TCP/IP networks. Live web access is manage the successful delivery to these satellite platform, SID had the required BBC Digital services. schedules for electronic programme guides and for the BBC s EPG editorial output. They have to manage approximately also provided to the database. Because there are so many different platforms. The database has been designed to accommodate a hierarchical storage capacity to cope. But no single BBC source could be found for the THE FUTURE associated metadata 30 live schedules for network and sources of information (the historical service structure, which will in future relevant basic schedules. We have SID is already a critical part of the e.g. genres, ancillary services, national television and radio. legacy of the analogue system), and allow the BBC s complex series of defined and implemented a new broadcast chain. It is the key supplier of conditional access. The system is implemented as a there are several destinations, all of national and regional opt-outs to be interface between the SID database and suitable metadata to support home Real-time delivery of trigger traditional client server model. Users which were set up using different modelled when the GUI is Broadcasting Data Services (BDS) to storage and virtual services. It will events to platform operators access the system through a custom- standards, SID is complex. Much of the further updated. enable the downloading over the ensure BBC programmes are promoted to support reactive now/next written graphical user interface (GUI). complexity is bound up in the number BBC programme schedules tend internet of suitable schedules. in a way most advantageous to the BBC type services. Servers are used to run an Oracle of operational interfaces. to be very reactive to allow for In the multichannel environment it whilst retaining accuracy, a traditional database and support the delivery of SID has evolved considerably since programme overruns and schedule is essential to give viewers and listeners strength of the BBC. the initial system required to support changes when circumstances dictate. better ways of locating BBC content. SID will continue to evolve to SID interfaces Inputs: PICS Import of raw TV schedule use the start of our satellite services. The launch of terrestrial television with its associated regionality and new interface A key requirement for the system is to manage schedule-timing variations automatically by monitoring the playout The BBC s Navigator project is the response. SID has been chosen as the source of data to support the initial handle changing requirements. The challenge is to ensure that these developments are compatible across Broadcasting data services Compass Import of raw radio schedules Real-time monitoring of TV playout systems to ONdigital s system resulted in the need to redesign both the GUI and database. Terrestrial services were system and adjusting the sending of triggers to mark the start of programmes accordingly. This facility Online Navigator offering. Once again SID has demonstrated its flexibility. We have enhanced the GUI and database to the range of platforms SID supports. It has been suggested that since SID now supports navigation generally, it Outputs : BSkyB Delivery of schedules and triggers for satellite services ONdigital central collator Delivery of schedules for terrestrial services both for cross carriage and BBC multiplex Navigator Delivery of schedules to support BBC navigator CSM Insertion of service information directly into BBC digital TV broadcasts FTP Access to EPG schedules from applications which are not broadcast critical launched using a second database fed from content created for satellite. This interim solution was replaced in 1999 when a single combined system with an enhanced GUI and database were put into service. This gave the users a single application to create content for both is particularly important now that new digital home storage systems are being introduced. We have now implemented this functionality in SID for our network programmes. SID was initially conceived as a TV only system. When the BBC decided to carry the extra metadata needed to support the Navigator and we have created a system to deliver the relevant information. It is expected that SID will form the core of many of the BBC Navigator systems now being planned should be renamed Schedule Interface for Navigation SIN, now that sounds a lot more fun! 52 APRIL 1999 MARCH 2000 BBC R&D ANNUAL REVIEW 53

11 The BBC, in common with a number of other broadcasters, is transmitting an increasing proportion of its digital TV output in widescreen, 16:9 format. Sales of widescreen TV sets are buoyant and surveys have indicated that about a quarter of digital TV viewers are watching on widescreen sets. However, most archive material and many new commissions have to be transmitted in 4:3 format and, of course, most digital viewers are still watching on 4:3 aspect ratio sets. generations of coders impose a half second uncertainty in the timing of the change of state of this flag. This creates a disturbance whenever there is a format change, e.g. between 16:9 and 4:3, which is likely to be disturbing to viewers. PUTTING IT INTO PRACTICE The video decoders fitted in set-top boxes (or integrated TV sets) allow for the processing of widescreen pictures so that they can be displayed on 4:3 screens. The current options are either to display a centre cut-out (where information at the edge of the picture Descriptors transmitted by the broadcaster, is defined in the UK Digital Television Group s D-Book. Whilst we still generate material in all formats, and people have all types of display, there is potential for things to go not quite right. Not only have we been directly involved in the Active Format Descriptors is discarded) or a deep letter-box formulation of the descriptors, we have Regardless of the shape of their TV format the way in which the Active Format Descriptors provide which shows the full 16:9 frame but had to put a lot of effort into the screen, many viewers do not like to see producers and directors intended. supplementary signalling options. They with black bands at the top and bottom education of all involved. This has large areas of black and prefer to watch Thankfully help is at hand in the form of allow for the inclusion of information of the 4:3 raster. involved promotion of the standards, stretched or zoomed picture. Other additional signalling embedded within describing how the transmitted raster is Future decoders, available from late checking the conformance of set-top viewers prefer to see undistorted the digital TV data stream, to signal to filled. This includes an indication of the 2000, will have the option to process boxes, as well as providing explanatory pictures (whether full-frame or not) set-top boxes and integrated digital TV active frame as well as whether this the picture to display a shallow (14:9) guidelines and test streams. regardless of what shape picture is receivers the various format/display includes a protected area. For example, letterbox which offers a good Nevertheless, the standards were being broadcast. options, so that taking into account drama is usually shot on a 16:9 raster compromise between the two options not always applied consistently, and this With a number of aspect ratio any viewer preferences, the but containing a protected 14:9 area currently available. has given rise to many of the problems options available to the broadcaster, a presentation is optimised. whereas sport is shot with a protected In addition to the processing experienced by viewers. number of picture processing options available in set-top boxes and similar but separate facilities in TV displays SIGNALLING AVAILABLE TO THE BROADCASTER 4:3 area. Active Format Descriptors are used in conjunction with the aspect ratio flag to define appropriate available in the decoder, the TV display also allows manipulation of the picture shape by altering the scan in either the We are trying to work with the industry and individual manufacturers to resolve problems where they exist. As a for manipulating the displayed picture, The MPEG aspect ratio flag behaviour for both the video decoder horizontal or vertical direction (or result of this work, all terrestrial set- it is little wonder that many viewers A flag is included in the MPEG within the Set-Top Box and the TV both). This would allow, for instance, a top boxes will be compliant following have expressed some frustration at broadcast signal which allows the display. This helps to present viewers 4:3 picture to be zoomed so that the software downloads in early 2000 and the difficulty (or in some cases shape of the coded raster (16:9 or 4:3) with a sensible range of picture display viewer sees a full display (but of course satellite set-top boxes should become inability) of setting their preferred to be signalled. options. They also permit more the top and bottom of the transmitted compliant during picture display format. This does not give the receiver accurate timing of the processing, thus picture are cropped). Hopefully cable set-top boxes As broadcasters, we want to ensure enough information to be able to avoiding some of the glitches that The intended behaviour of decoder should largely be compliant at launch. that our programmes are enjoyed by exercise sufficient control over the were common with systems using only and display, taking into account the the viewer in the optimum presentation display format. In addition, early the Aspect Ratio Flag. raster flag and any Active Format 54 APRIL 1999 MARCH 2000 BBC R&D ANNUAL REVIEW 55