Choose the right HD graphics card

The benefit of HDMI over DVI, though, is its ability to transport digital audio, providing the convenience of a single cable for audio and video.

However, since PC graphics cards don’t generate audio, those which offer HDMI ports also feature an SPDIF input to aggregate the audio signal from your sound card.

Both the Sapphire and MSI cards come with SPDIF connectivity for either internal audio headers or external coaxial RCA jacks.

Bandwidth limitations of the SPDIF interface mean it’s unable to handle the uncompressed or high bit rate multichannel audio options of certain Blu-ray or HD-DVD titles, but luckily the movies also have conventional 5.1 Dolby or DTS soundtracks for backwards-compatibility.

Both cards also feature additional video outputs: the Sapphire card has an analogue VGA port, while the MSI card has a DVI-I port with a VGA adapter. Not to be left out, the Sapphire card comes with an HDMI-to-DVI adapter and also an HDMI cable. The Sapphire card is available for about £65 from Ebuyer.co.uk, while the MSI card is available from Quietpc.com for about £55.

Test setup
We tested each card in a media PC system built using an Asus N4L-VM DH motherboard fitted with an Intel Core Duo T2600 mobile processor, clocked at 2.16GHz and 1GB of Crucial DDR-II memory. A Sony BWU-100A drive was connected for Blu-ray playback.

The system was running Windows XP Media Center Edition 2005 from a 300GB Seagate Barracuda 7200.8 Serial Ata hard disk. The latest drivers from ATI and Nvidia were installed (versions 7.3 and 93.71 respectively), and the playback tests conducted using the most recent build of Power DVD Ultra, version 7.3. A Dell 2407WFP monitor with a DVI connection was used for tests in the 720p and 1080p high-definition formats (1,280x720 and 1,920x1,080 respectively at 60Hz).

To test high-definition video playback, we used the latest James Bond film, Casino Royale, on Blu-ray, which is encoded using the AVC format. For reference we used chapter two, which starts with the chase sequence in Madagascar played back at full screen.

During this sequence, the bit rate typically varies between 20Mbits/sec and 30Mbits/sec as measured by Power DVD. This presents a reasonable challenge to decoding systems, albeit not in the same league as X Men III on Blu-ray, which averages 40Mbits/sec – see this month’s Performance column.

Results
While this test focused on high-definition video playback, we also briefly tested both cards for 3D performance. Using 3Dmark05 with its default settings (1,024x768 resolution without anti-aliasing), the Sapphire and MSI cards scored 4,461 and 2,227 respectively. That’s a big difference, although neither can be described as top-of-the-range gaming cards; and again the focus of this test was video.

With the Sapphire card installed and the desktop set to 1,280x720 at 60Hz to emulate the 720p format, the Blu-ray playback was smooth and uninterrupted, with Task Manager measuring the CPU usage between 65 and 84 per cent. Switching to a desktop resolution of 1,920x1,080 at 60Hz to emulate the 1080p format caused CPU usage to vary between 75 and 90 per cent, but playback remained smooth.

With the MSI card fitted and the desktop set to emulate 720p, the CPU usage was measured at 68-91 per cent. This was higher than the Sapphire card, but still delivered a smooth experience. Increasing the desktop to emulate 1080p, though, the CPU usage never fell below 83 per cent and frequently hit the mid-to-high 90s. We wouldn’t exactly describe the result as choppy, but video playback at this setting certainly wasn’t smooth.