BSkyB has confirmed that it will support both 720 and 1080 line formats for high definition television, with the choice left available to broadcasters.

The UK satellite broadcaster is building its high definition system to support both 720 line progressive (720p/50) and 1080 interlaced (1080i/25) formats, and is specifying its set-top box, due to be launched commercially in 2006, to be able to handle both.

The relative merits of the different approaches are the subject of some industry debate. The first commercial high definition service in Europe was launched using a 1080 line interlaced format, but the European Broadcasting Union has controversially since recommended the 720 line progressive format. A 1080 progressive format would arguably offer the benefits of both, but equipment is currently unavailable to support this and it would require much higher bandwidth.

Sky believes that a progressively scanned picture format is better suited for the delivery of HDTV to large screen flat panel displays that are increasingly prevalent. It recognises that 720 lines is currently the maximum progressively scanned format deployed in consumer decoding and display devices expected to be widely available over the next few years. However, Sky acknowledges that, for some types of programming, the higher screen resolution offered by the 1080 line interlaced format may be preferable. The dual format approach sensibly keeps the options open for both Sky and other broadcasters.

There is still no news of which compression scheme Sky will adopt, as it continues to evaluate the benefits of MPEG-4 part 10 standard, also known as H.264, against VC-1, which is based on Microsoft Windows Media 9.

Perhaps more importantly for consumers, Sky has confirmed that its high-definition set-top decoder will be use an HDMI interface as the ‘primary means of connecting to an HD display’. The High-bandwidth Digital Multimedia Interface is a digital connector that carries both digital audio and video over a single cable, and can also be connected using an adapter cable to DVI displays as supported by many computers.

Significantly, it is expected that most HDTV content will be protected by HDCP or High Definition Content Protection, and will therefore only be capable of being viewed on display devices that support HDCP. This is intended to provide digital copyright protection right through to the display device, eliminating the vulnerability of the so-called ‘analogue hole’.

BSkyB, together with SES Astra and other European pay television operators, have recently defined an ‘HD ready’ label for compatible display devices. The message to consumers is that if they’re in the market for a large screen television and they want it to be compatible with the high-definition service from Sky, they should check the specifications carefully and avoid any apparent bargains in the Christmas sales.