By June 2007 the BBC's high definition channel will be one year old. For those with HD-ready screens and the right equipment, it's quickly become a familiar part of the TV line-up.
Viewers can currently watch stunning HD broadcasts of new or recent series such as Planet Earth, Torchwood, Coast and Robin Hood, not to mention a variety of live events, from football and Six Nations Rugby to Wimbledon and the Proms.
The channel is currently available on satellite, cable and - to a few hundred trialists like me in London - digital terrestrial television (a.k.a. Freeview ), where groundbreaking test transmissions have been taking place since the summer of 2006. Despite this innovation, a question mark hangs over the future of high-definition broadcasts over digital terrestrial TV.
Why? Because the BBC is about to propose a permanent HD service and digital terrestrial is by far the weakest platform to base it on. The trial BBC HD channel was originally intended to run for just 12 months, though the BBC has asked Ofcom for an extension beyond June 2007. The BBC Trust will also decide if the channel can stay on air while the proposals are considered, which could take until the final quarter of 2007.
The BBC's head of HDTV, Seetha Kumar, told a trade conference in February 2007 that: "Any BBC HD service would inevitably launch with limited content and would be based, as the trial has been, solely on HD originations. Its growth would be evolutionary as more native HD content comes on stream.
"BBC HD broadcasting," she added, "will not be equivalent on all platforms at launch, because of the insurmountable restrictions on terrestrial capacity while we have dual analogue and digital transmission. Our aspiration over time [is] to be universally available on all technically capable platforms, as far as possible."
Terrestrial capacity is a big problem, given the government's intention to auction the spare broadcasting spectrum after the analogue switch-off in 2012. Nothing will happen before this date. Ofcom's decision, and whether it will bow to demands from HDTV advocates that a third of the spectrum should be 'ring-fenced' for HD Freeview, is being debated now.
There's more about the debate on a new website launched by our colleagues over at What Satellite & Digital TV. You can find it at: www.savefreeviewhd.com .
Why Freeview HD needs saving
A free-to-air HD service is arguably something that viewers are crying out for. Intensive testing of high-definition digital terrestrial broadcasts ran between June and December 2006. 450 volunteers in the Greater London area were given set-top boxes supplied by Advanced Digital Broadcast (using the i-CAN brand) and Humax.
The ADB i-CAN 3800T and Humax HDCI-2000T boxes contained new MPEG-4/AVC decoding technology and an HDMI output. Standard Freeview boxes weren't able to receive the service.
The HD trial was broadcast over two multiplexes. One was dedicated to the BBC HD channel, the other multiplex was shared between test HD channels from ITV, Channel 4 and Five. ITV's output included archive film or TV shows such as Space 1999 shot on 35mm and freshly transferred to HD format.
Channel Four showcased US HD imports, including big shows such as Lost and Desperate Housewives, while Five added House and CSI (to date, the only time these Five hits have been available on British HDTV).
Of these test channels, only BBC HD is still running - as it also does on satellite and cable - with a few further digital terrestrial tests taking place, such as the effect of bitrate alterations on picture quality.
Earlier tests compared the difference between broadcasting in 720p instead of the 1080i HD format. Aside from a few minor glitches, similar to any caused by localised low-power digital terrestrial broadcasts, the trial was declared a success by technicians and viewers alike, with 92 percent of trialists giving HD pictures at least an 8 out of 10 for quality.
A second phase of the trial will experiment with subtitling, EPG interactivity and using standard definition (SD) video via MPEG-4 (in contrast to the older MPEG-2 codec used by Freeview).
The codec test is significant. MPEG-4 broadcasts will require less bandwidth, thereby freeing up more space for extra SD channels or a limited number of HD channels to be launched in the future. But again, as all previously sold Freeview boxes use the older (and fatter) MPEG-2 codec, the 6.5 million homes that have already bought into Freeview would need to buy a new MPEG-4 box before they could receive such transmissions.
ITV, C4 and Five are also exploring options for more HD broadcasts, buoyed no doubt by the fact that 98 per cent of the HD trialists last year overwhelmingly supported an over-the-air HD service being available now. There were also strong views in favour of public broadcasters being at the forefront of HD delivery and for any HD service to be free.
Current proposals for a ' Freesat ' system (digital channels via satellite at no charge except for a minimal installation fee) could be one solution for free HD in the UK. However, the BBC is concerned about Freeview's fate if it cannot carry HD in the future.
In its report, the BBC warned: "The migration of viewers away from the DTT platform in search of valued HD services would undermine the investments made."
More information about the Freeview HD trial can be found on the BBC's website . Ian Calcutt