Watch high-definition content on your PC

With HD DVD and Blu-ray drives becoming ever more affordable for the PC, watching content in high definition is now more attractive than ever

The PAL TV standard must have seemed impressive when it first started delivering colour TV in the UK back in 1967. But 40 years on its feeble 576 scan line resolution is looking poor.

By comparison, high-definition's maximum 1920 x 1080 resolution looks pretty spectacular. But if you're keen on playing high-definition content on your PC - through a Blu-ray or HD DVD disc, the resolution isn't such good news.

Conventional DVDs require only an 8Mbps video stream, but try playing a Blu-ray disc and your PC will need to handle 20, 30 or even 40 Mbps. All this, without losing a single frame or having audio dropouts, for potentially hours on end. It's pushing current technology to the limits.

Constantly reading a Blu-ray video stream at up to 40Mbps is only one of the tasks your PC has to perform. That stream also has to be decoded from its original format (probably MPEG-2 or MPEG-4) - enough in itself to keep your PC very busy.

Thankfully, Nvidia's latest graphics cards can handle the decoding themselves. This frees up your CPU to do other things, reducing the chance of dropped frames, and you'll also use less power. This is handy if you're hoping to watch high-definition movies on a notebook, for example.

Decoder competition

ATi fought back with the Unified Video Decoder - part of its Avivo HD technology. This is a GPU module that also decodes HDTV, Blu-ray, HD DVD and MPEG-4.

Right now there's little to choose between their performances. It's worth noting that in both cases, this hardware acceleration currently only works on Windows Vista.

The aim of the new cards isn't just to improve performance, though. They also employ a few tricks to improve picture content - something that's rather more difficult to measure.

Image processing

Current analogue TV uses a technique called interlacing to display images, where it draws the odd horizontal scan lines for one frame and then the even ones for the next. You don't really see anything strange going on, though the technique can occasionally produce unpleasant motion artefacts.

Both PureVideo and Avivo offer a variety of image-processing techniques to resize and sharpen pictures, remove noise and correct colours.

These have little effect on already impressive 1920 x 1080 images, but can produce some noticeable improvements on lower-quality material.

The new HD cards do their best to improve video quality, then, but how much of this will make it to your monitor is another matter. If your Blu-ray or HD DVD disc has its ICT (Image Constraint Token) flag set then viewing the image over an analogue VGA connection will only give you a 960 x 540 resolution picture.

This hasn't happened yet, and the rumour is that it won't until 2010, but there are no guarantees. The studios have another cannon in their armoury in the form of the Digital Only Token, which will block analogue output altogether.

Future requirements

Future-proof playback requires that you use hardware supporting High Definition Content Protection (HDCP), while watching over a DVI or HDMI connection, then. This isn't easy to achieve, though, because every link in the chain must support it: your optical drive, graphics card, even monitor (or TV if you're hoping to use the Blu-ray drive there).

It makes sense to look for HDCP-compliance when you're buying a new PC, then. But if you're after high-definition on the cheap then a Blu-ray or HD DVD drive is currently all that you need.

Nvidia's PureVideo HD and ATi's Avivo can significantly reduce your CPU load and improve image quality, but they're not essential and at the moment there's no requirement for an HDCP display at all.

Furthermore, worries over a user backlash could mean that HDCP isn't actually implemented for a few years to come. So if you're happy with the high-definition image quality from your analogue connection, then sit back and enjoy it: you may not have to buy anything else for quite some time.