Last month we discussed how nonvideo centric services for DTV are being supported under the umbrella of data broadcasting, that technology structured by – and described within – the ATSC A/90 data broadcast framework. The software environment for A/90’s work is contained under the description of the Digital TV Application Software Environment (DASE); in Europe the DVB equivalent is the Media Home Platform (MHP). We pick up the topic on data broadcasting at the data server, one of the elements for interactive and enhanced television systems.
Data servers for DTV data broadcasting applications must produce a datastream that is packetized and encapsulated according to the A/90 standard. The syntax for ATSC A/90 data broadcasting compliance is structured with the elements and applications developed, in part, under DASE’s application and interoperability services.
Data servers output their compliant stream(s) directly into the emission multiplexer at the time of distribution to the broadcast transmission path. Depending on the particular ATSC encoder manufacturer’s architecture, the emission multiplexer may be an integral unit or, in most cases, an outboard interface that produces a 19.4 Mbps ATSC stream in either ASI form or SSI (SMPTE 310M) standard.
ONE WAY OR ANOTHER
For one-way activities in a traditional data broadcast model, those elements of DASE Level One – designated as local interaction – are sufficient to handle a modest set of features. Local interaction – also referred to as ‘enhanced television’ – introduces activities associated with the local set-top box (STB), whereby the viewer can enjoy supplemental activities associated with the particular program stream being watched at that moment. Such activities might include ‘play along games’ like Jeopardy, Who Wants to be a Millionaire and NFL Monday Night Football.
The signals necessary for DASE Level One features are generally background downloaded as supplemental information categorized under one of two classes. The data services profiles in an ATSC multiplex fall into one of these two classes of profiles, described in Table 1.
(click thumbnail)Table 1: Data Services Profiles
Operationally, data is demodulated from the DTV carrier and either stored in the STB memory or is continuously presented in a carousel format that allows the data to be routinely refreshed during the DTV stream with which it is associated.
Depending on the type of STB or the software development associated with the feature, this data can be stored for future uses or retained only during the program it is associated with and then purged or overwritten without any user interaction.
Today, experiments in one-way activities – intended as alternative enhancements to the television viewing experience – are being implemented as accompaniments to analog NTSC television. Most of these activities utilize the Internet in "two-way activities" mode. The Internet content is designed to keep the viewer involved with that particular on-air program rather than luring them to other threads on the Web.
Other activities include the signaling of URL paths in the VBI – for example, WebTV – thus creating a pseudo-interactive experience married between a secondary platform and a conventional television display.
When implemented for DTV data broadcasting transmissions, background downloads to set-top boxes will allow the viewer to interact with the receiver/display in order to obtain sports statistics, product information, enhanced program guides, local weather and even traffic updates.
VIRTUAL CHANNELS
For those now experimenting with DTV, one of the easier-to-implement concepts is to steer viewers to a different ‘virtual channel’ (one in the same ATSC multiplex), where they obtain additional information at another, lower bit-rate, program stream in the form of static graphics, simple animated depictions or even talking head/barker channels.
Because the viewer is still watching a program or program stream from the same primary channel originator, the broadcaster retains control over content, impact, advertising, etc., on that channel. Hence, there is no risk of losing the viewer to another ATSC broadcast channel or to an uncontrolled Web page.
(click thumbnail)Fig. 1
Although the use of audio/video virtual channels is suitable for this function, the hardware involved at the studio requires additional video/audio processors, MPEG encoders and the ATSC multiplexer.
The DTV data broadcasting approach takes the content from a data server and injects it into the final emission multiplex before transmission — freeing the valuable video/data space for additional full-featured programming, including supplemental data for that program proper. It is then presented as backgrounds, graphics and audio, separate from a primary or secondary video/audio presentation.
MULTIPLEXING
Fig. 1 depicts the broadcast station’s architecture from video/audio encoders through the multiplexer to transmission. Note that the data server(s) provide information to the program multiplexer and to the emission multiplexer, under control of the previously mentioned multiplexer manager. In some instances additional data could be provided from a video server’s metadata program stream (“data *” in Fig. 1), which is specific to the audio/video content, on to the program multiplexer. This data would be further integrated into the program multiplexer and harmonized with DASE software structures carried on the external data servers.
