Gordon Laing

The long-awaited launch of High-Definition Television (HDTV) broadcasting in the UK has brought relief to some and frustration to others.

It’s great for video enthusiasts, but infuriating for those who don’t receive cable in their area and aren’t allowed, or don’t want to mount a dish on their building.

I fall into both camps, longing to view my favourite movies, sport and documentaries in HD, but am unable to receive them in my current home. This is why the BBC’s technical trial for receiving HD programmes through a normal rooftop antenna is so exciting.

HD volunteers
A short while ago, the Corporation recruited a few hundred volunteers to see if it was possible to broadcast HD using spare bandwidth on the existing Freeview digital TV platform.

Fellow broadcasters ITV, Channel 4 and five joined forces with the BBC to pump out selected HD shows and demos across the London area which, in theory, could be received by anyone in range with a standard TV antenna, but only decoded by those volunteers equipped with a special set-top box.

The fact that these signals are within the reach of more than seven million Londoners, but only enjoyed by the select few with the set-top box, is enough to get any enthusiast racking their brains.

The existing Freeview platform may employ the same Mpeg2 video compression system as DVDs, but to the tuner components it’s just a stream of noughts and ones arriving through an antenna.

It’s the processor inside the set-top box that has to make sense of it all, decoding the stream into video and audio signals using the more sophisticated H.264 compression system.

Like Freeview boxes and TVs, the digital tuners fitted to many media PCs can also receive any broadcast data stream.

The difference with a media PC is that the HD trial data could be recorded onto a hard disk then decoded by a suitably configured system. In theory, any one with a PC and digital tuner in range of the London transmitters could enjoy the free-to-air HD trial through their standard antenna.

And even though the trial is only for a few hours a day and will expire in less than a year, it remains a compelling experiment for media PC enthusiasts.

Project success
Like all projects of this ilk, there’s no guarantee it will work. Early reports show some cards working better than others, while lack of support in front ends, such as Windows Media Center Edition, have forced enthusiasts to employ programs like Tsreader to record the H.264 streams.

The biggest surprise for many is the kind of equipment required to decode H.264 into smooth video. The first step is to install an appropriate H.264 software decoder, and most find Cyberlink’s PowerDVD 7 Deluxe does the trick.

The problem is the amount of processing muscle demanded for the numbercrunching. H.264 is complex stuff, incorporating several technologies beyond Mpeg2 to deliver improved quality. It can look great but requires considerably more decoding horsepower. Even the very latest CPUs are barely capable of doing the job.

Looking back to the launch of DVD, we were in the same situation with Mpeg2. Owners of state-of-the-art 500MHz PCs almost wept when they failed to cope with this latest video technology. Relief came from graphics cards that incorporated hardware acceleration to take the strain from the main CPU.

Many uses
Today, graphics chipsets are once again coming to the rescue for decoding HD video in the H.264 format – and if this sounds like a lot of hassle just to enjoy a restricted trial, don’t forget that H.264 is also used for satellite HD broadcasts in the UK and forthcoming prerecorded HD-DVD content.

Graphics chipsets based on the ATI X1000 or above, or Nvidia 6150 or above feature built-in H.264 hardware acceleration. There are exceptions; ATI and Nvidia can provide more details on H.264 support.

So being HD ready in this instance isn’t just about having the right display and connectivity. It’s also about having the appropriate processing muscle to decode the signal. And the answer lies not with having the fastest CPU around, but the right graphics card.

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