A quick guide to interactive television

For operators to implement iTV, the most important decision is which middleware to choose
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The term “interactive TV” is used to cover a wide range of user experiences, including:

  • Video on demand (VOD).
  • Personal/digital video recorders (D/PVRs).
  • Enhanced TV (eTV).
  • 24/7 (sometimes call “walled garden” or “digital text” services).
  • TV commerce (tCommerce).
  • Games.

VOD and PVR may not always be thought of as iTV, but they rely on iTV technology. They are different from the other categories as platform operators usually implement them with no technical involvement from content providers.

PVRs use a hard drive in the set-top box (STB) to record content from the conventional broadcast stream. The main thing that the PVR needs is a reliable source of program schedule data because it uses this to time the recordings. If it is to do “speculative” recording, it also needs good “genre” information about programs so it can guess what the viewer might like based on his or her preferences or previous choices.

VOD requires significant integration between the headend and the STB. The STB must have an application that allows it to browse the library of titles and to send “VCR” controls to the VOD server, e.g. to pause or rewind the video stream.

24/7 services often consist of news, sport or weather material and are called 24/7 because they are always available (in contrast to eTV or video synchronous services). Games could be considered as part of the 24/7 offering. We have listed them separately to emphasize their importance for revenue generation as viewers pay money to play. Games require a return path for revenue collection and leader boards.

tCommerce services are provided by retailers. Home banking has not been a commercial success. tCommerce requires a secure return path.

eTV is content broadcast to enhance an event or a program, although it is not synchronous with the video. Examples of this include:

  • Scoreboards and statistics for a sports game or tournament.
  • Video loops allowing the viewer to “surf” to interesting content at will, e.g. highlights of a sports game or news headlines.
  • Multiple camera angles offering supplementary views of sporting content, as well as the main studio output.
  • Multi-screen offering a view of several games in a tournament with scores overlaid. Audio can be switched to follow as the viewer moves the cursors between video feeds.

Synchronized enhancements are the most technically sophisticated and allow enhancements to “pop-up” at a certain time relative to the linear video. The most popular uses for this capability are interactive quiz shows and voting. These are often used with live programs where the results are sent up the return path, collated and announced almost instantly as part of the program.

A common use of synchronized enhancements for recorded programs is “multi-stream,” where a program consists of multiple video streams, and the application switches between them depending on how the viewer responds to questions.

A popular example are the BBC natural history programs, where viewers have to guess what an animal would do to survive a situation. Depending on their answers, viewers get switched to a video stream that tells them if they are “dead” or “alive.”

Operators' view

For operators to implement iTV, the most important decision is which middleware to choose. An important factor is the STBs they have or plan to acquire, as STB integration is the most costly and risky aspect of deploying middleware. In these cost-conscious times, operators are likely to be looking at small-footprint STBs, and most of the middleware vendors now offer solutions for these.

Figure 1. Simplified view of an MPEG-2 transport stream with interactive TV data and applications. Click here to see an enlarged diagram.

The other important factor for deploying a middleware is the supply of content, and the best way to ensure a good supply of content is to choose a popular middleware. This is particularly important for small to mid-size operators whose subscriber bases may not tempt content providers to integration with another middleware. OpenTV and NDS now dominate the market for middleware. They both use a broadcast-oriented architecture and can offer support for a return path, e.g. for shopping, voting, etc. The iTV applications and data are broadcast on their own packet ID (PID) streams along with the TV services. (See Figure 1.)

Figure 2 shows a simplified architecture of an iTV STB. The STB vendor provides the hardware drivers. The real-time operating system (RTOS) may be provided by the STB vendor, or it may be integrated into the middleware, especially in the case of small-footprint STBs.

Figure 2. Simplified view of an iTV STB architecture.

The interface between the middle-ware and the applications defines an application programming interface (API) for the interactive applications. One of the purposes of middleware is to provide an abstracted environment so that applications can run on many different models of STBs without modification.

It's important to remember that the electronic program guide is implemented as an interactive application, albeit a rather special one. The EPG is usually embedded in the STB's persistent flash memory. Other applications are loaded as required from the broadcast stream and so are shown as a dotted box in the diagram. Most middleware can associate interactive applications with TV channels, so applications load when the viewer tunes to that channel.

Most STBs have a return path. For cable STBs, this is often a cable modem, although some boxes use a PSTN modem to save cost. Satellite boxes usually use a PSTN modem, although DSL is a future possibility. The return path can be used to send votes and quiz answers back for live shows. It can be used for transactional services such as TV banking, where personal data is passed in both directions. It is also used for chargeable interactive services, such as games. Although the games are broadcast over the air, revenue is gathered using the return path. In the case of cable, the game reports that it has been played and the ID of the STB. This information is compiled into the billing run and added to the cable bill. In the case of a PSTN return path, the game calls a premium rate number.

By broadcaster, we mean the information provider. This may be a conventional broadcaster, a third party or the platform operator. Most delivery platforms will carry interactive content from all three sources.

Broadcasters' view

The BBC is rightly regarded as a leader in the field of distributing content to multiple delivery platforms. It provides content to:

  • BSkyB, which operates a satellite service that uses OpenTV.
  • The cable operators, which use Liberate.
  • Digital terrestrial, which uses MHEG-5 (although this is not widely used outside the UK).

When the BBC launched its services a couple of years ago, it could not find suitable products to manage this process. As a result, it developed its own in-house solution. (See Figure 3.) Although the industry has matured since then, many broadcasters are working with bespoke solutions.

Figure 3. Simplified view of the BBC multi-platform playout system. Click here to see an enlarged diagram.

The BBC content entry system collates content into XML feeds. These feeds are then scheduled for playout by the content management system via filters that render the content for each delivery platform. The BBC also has built a modular, configurable application that can display a wide range of content. There are versions of this application for each of the delivery platforms, and the application can be configured by the content management system, meaning that the reconfiguration can be scheduled around events. Other broadcasters and vendors also have produced reusable applications to display content, although most of these focus on one delivery platform.

It should not come as a surprise that iTV applications require an extensive test cycle before release onto live platforms. Usually, the broadcaster and the operator will both do test cycles. Middleware provides a common API for applications across STB models, but hardware differences are still significant, so test centers still have a wide selection (if not all) of the available STBs to check compatibility. This can run into dozens or even hundreds of models, depending on the platform.

The iTV industry is now maturing to the point where content providers routinely deliver significant amounts of high-quality content in the leading market places. There is still some way to go before programme makers and viewers handle iTV in the same familiar way that they handle linear TV.

Testing and quality control


David Short is a technical architect working on the design of new DTV systems. He also ia a member ofBroadcastProjects.com, an alliance of independent consultants. For more information, visitwww.broadcastprojects.com.