ABSTRACT
Data broadcast has generally referred to any information carried along with the video or audio signal that is not the video or audio coding itself. The classic example of ‘data’ associated with television is teletext.1 However, there is other information that falls into this category, including subtitling and captioning. ‘Data’ is often also generally used to refer to literally anything encoded in the Vertical Blanking Interval (VBI) of the analogue television signal, including what we today recognise more formally as metadata. More commonly today, there is a distinction drawn between
metadata (information about the video and audio) and data ‘essence’.2 The latter refers to data items that convey their own information to the viewer and not just information about the video or audio. For example, a digital programme identifier encoded into the VBI relates to the video and audio, has no intrinsic value on its own, and would rarely be displayed to the viewer. It is thus considered metadata. In contrast, teletext is considered data essence since it has value on its own. Electronic Programme Guide (EPG) data is technically metadata (information about the video and audio programming), but is less clearly so due to the sheer volume of information and its intrinsic value to the viewer. This chapter, data broadcast, is concerned with data essence and not metadata, and the use of the term data here means data essence. The introduction of digital television systems enables a
robust array of data broadcasting possibilities. This is primarily due both to the fact that the broadcast is inherently digital, and that there is so much more bandwidth available. Being inherently digital makes the insertion and extraction of data easier, and provides a more robust (less error prone) delivery. In contrast, analogue VBI has very limited bandwidth and is quite error prone, especially when the signal was not strong at the receiving equipment. Reliable delivery in the analogue environment often required various FEC techniques, which used up even more bandwidth. Digital television systems have defined a set of building blocks, or infrastructure, in which to carry some basic data models. While every digital transport has defined their own unique details, the basic data models that have been universally defined are: Internet Protocol (IP) data
packets, files (analogous to a computer file system), streams of bytes, and ‘triggers’. All of these can be thought of in aggregate as a data broadcast infrastructure, which can then be used for the design and delivery of specific data services to the viewer. Data services are an application of data broadcasting that results in some experience for the viewer. Also, using this data infrastructure, interactive television (ITV) systems such as Digital Video Broadcast Multimedia Home Platform (DVB MHP)3 and the Advanced Television Systems Committee DTV Application Software Environment (ATSC DASE)4 can add another layer of ‘tools’ for the ultimate data service provider.
