COLIN PRIOR /
05.01.2008 12:00 PM
Interactive TV platforms

As anyone who has followed the interactive television sector over the past 15 years or so will know, it has not always been smooth sailing from either a technological or business model perspective. But as digital networks spread, the need for viewers to be able to interact with their content has grown. Now it is a case of being a necessity rather than a luxury as we move to an on-demand world. Equally, from a broadcaster, network operator or regulator perspective in the information age, it is a shortsighted decision if no interactive middleware is specified at the time of a new network deployment or upgrade.

It also now widely accepted — and market proven — that in order to achieve desirable economies of scale and real audience reach, deploying a public standards-based system is the way forward. Interactive TV works only when all (or almost all) the receivers in a market have middleware installed. It facilitates widespread adoption, multiple vendors at each point on the industry chain, and price and performance competition. Of course, it also requires a conformance scheme to ensure interoperability and ease of use.

The public standard of choice is MHEG-5. More than 27 million receivers have sold in the UK for the DVB-T service Freeview. Satellite and DVB-T-based Freeview services run in New Zealand. TVB in Hong Kong deploys the standard, as do the UK's new Freesat platform and Digicable PayTV operator in India. The growth path is clear.

As with any successful standard, it needs a firm technological roadmap for future developments. This article will provide a brief update of how MHEG-5 works and will then explore the latest developments and the benefits that they will provide.

Interactive television middleware

Interactive TV systems require software components at both the transmission (playout center or headend) and reception points (set-top box or integrated digital receiver). MHEG-5 is an open standard middleware — or application program interface (API) — designed specifically for low-cost memory constrained devices particularly suited for digital interactive TV (iTV) services.

MHEG is a public standard with no known intellectual property rights issues and associated license fees. Originally developed and standardized by ISO in the mid-1990s as part of the DAVIC standardization effort to support interactivity and navigation for video-on-demand services, MHEG-5 is now a mature technology.

With the latest standard — UK Profile 1.06 — a strong conformance test suite has been developed by the UK Digital Television Group, ensuring interoperability for receiver manufacturers, broadcasters and content creators. The UK Profile, or its ETSI equivalent, provides a baseline specification that can, and has been, extended for other MHEG deployments worldwide such as for Freeview New Zealand.

The MHEG-5 end-to-end system is simple, and its client software can be implemented in a wide range of low-cost digital TV receivers. The client software consists of an MHEG engine that interprets MHEG applications and presents information delivered to it via a broadcast file system or via an IP return channel. MHEG enables interaction between the user and the application through the remote control. In some implementations, it allows the application to exchange information with a remote server via the IP connection.

Territory-specific profiles of the MHEG-5 standard, based on the UK Profile 1.06, are being progressively released to support different character sets and receiver requirements. Creating a country profile is really about agreeing character sets and the requirements behind that and which — if any — of the other new features are required. For memory and licensing reasons, broadcasters/regulators only want to use the character sets that they need for a given market because this keeps the receiver cost down, as opposed to putting in a global character set that country-specific broadcasters simply don't need. After all, broadcasters don't need to support Chinese when they are in Italy!

So far New Zealand has added a Maori character set and EPG key; there are Chinese language profiles for China, Hong Kong, Singapore and Taiwan. For Chinese, an external font is licensed separately from the middleware engine. Support for an Indian character set is also under way.

MHEG extensions

As mentioned, there are several other extensions to MHEG now being finalized. The first MHEG extension to examine is the Interaction Channel, or return path. The intention is that it will be rolled out in the UK and then in other markets. It provides an always-on return path that will allow broadcasters to offer additional services — more interactive content and secure commercial transactions among them. A key driver behind it is to allow content that is currently being delivered to PCs to be delivered to the TV in the living room. Viewers can use an MHEG-5 application to navigate around what the broadcaster is offering, and then it can be delivered over IP. This can either be via streaming or download with a push VOD model.

It provides an end-to-end system that detects whether a return path is available and provides broadcast-only services if none is detected. Where a return path is available, it seamlessly links the return path to the broadcast file system so that the same application can access additional content — video, audio, text and graphics. IP return-path enabled hybrid receivers offer much greater scope for delivering compelling content and services that significantly enhance the viewing experience. The Interaction Channel will also support transactions for viewer interaction for purchasing, voting and other participation TV formats, for example.

The UK's Digital Television Group's Interaction Channel Working Group is currently working with manufacturers and broadcasters on a new profile MHEG-5 for inclusion in the ETSI-MHEG specification and the UK DTG D-Book. By the time that you read this, a final specification may have been agreed.

The Interaction Channel will not allow Web access unless a broadcaster includes specific URLs. Users will find the experience transparent. If they have an IP connection, then they will be able to see a whole new set of options when they press the red button, for example.

While Freeview Playback — the DVR standard deployed by Freeview in the UK — has nothing directly to do with MHEG, it has successfully introduced the notion of content reference IDs (CRIDs), which are unique identifiers that are associated with a particular event or program. This information is broadcast in the DVB EIT Present/Following table. Instead of just making the PVR timer-based, it actually lets the recorder watch for the start and the end of the program, and it allows series links and recommendations.

Specification work is under way to integrate CRIDs with MHEG applications, such as an EPG to control the booking of recordings, offering broadcasters around the world a public-standards based integrated DVR.

Platform-wide EPGs

MHEG-5 based EPGs are another key development and have been deployed by Freeview in New Zealand. A platform-wide EPG, (unlike a set-top box resident EPG, which is subject to manufacturers' interpretation and implementation), it will look and behave the same on all receivers regardless of manufacturer. When carried on all channels in a platform, it offers consistency of user access to services, combined with the ability to launch with the current channel's data in view. As the EPG is under the operator's control, it also enables broadcasters to display advertising banners and sponsors' logos on the EPG if required. The best way to do this is to allow the EPG application to take inputs from many kinds of input data, which are processed using software to provide an efficient datastream for transmission. Compressing the information inside an Object Carousel makes it extremely bandwidth-efficient, especially when compared to EIT schedule-based EPG data.

Of course, HD developments have also been taking place. A DTG Working Group was established in 2007 to determine the changes required for the MHEG sections of the D-Book to allow receivers to implement MHEG in an HD broadcast environment. The specification for this is now complete, and it maintains backwards compatibility for legacy receivers. Additional features in the HD spec include:

  • MPEG-4 H.264/AVC video codec;

  • JPEG graphics support;

  • intelligent text rendering and square pixel format;

  • automatic selection between SD and HD assets depending on display capability; and

  • the assumption that 720 minimum vertical display resolution is HD-ready.

Common Interface Forum

Another recent development that reinforces the flexibility of MHEG-5 is the decision of the Common Interface Forum to specify its use in the next version of the conditional-access technology CI+. Common Interface (CI) was originally developed within the DVB to allow an external conditional-access unit to be plugged in. (CI has to be built-in to any TV above approximately 21in screen diagonal, though it varies across Europe.) The original CI implementation was not totally secure. There was a move within DVB towards CI-2, but that faltered about two years ago.

Some manufacturers — such as Neotion, Panasonic, Philips, Samsung and Sony — then formed the Common Interface Forum to develop CI+, a fully secure implementation of CI.

The Common Interface Forum has decided to provide more flexible information displays and has specified a subset of MHEG-5, without the DSM-CC file system, to do this. So essentially MHEG-5 will become the user interface for CI+ and will therefore be included in a huge number of iDTVs. This is significant because if a subset of MHEG-5 is being deployed, many manufacturers are likely to include the full version of MHEG-5.

MHEG-5 is an established technology that is growing in reach and capability on a daily basis. It benefits from a market needs-driven technological roadmap that provides a clear route for broadcasters/regulators into the future without forcing them to adopt all the extensions in one go.


Colin Prior is director of international sales at Strategy & Technology (S&T).



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