DVD decoders and you

Before we go into the nuts and bolts of DVD playback quality, there's something we need to clarify about how your PC plays DVDs: Windows needs a DVD mpeg2 decoder to do it.

The real interesting part is that Windows XP does NOT come with a DVD mpeg2 decoder. That means that if you install nothing but the Windows XP operating system on a computer with a DVD drive, it will not be able to play DVD video. You have to install a third-party MPEG2 decoder first.

This might have you scratching your head wondering how it is that you've been playing DVDs all this time without installing a decoder. Remember though that many manufacturers will tweak windows and pre-install software for their users. In addition, most aftermarket DVD players will come bundled with a DVD decoder. Software such as Nero, WinDVD or PowerDVD (to name a few) all install their own MPEG2 decoder. So even though it doesn't come with Windows, most PC owners have already paid for an MPEG2 decoder either directly or indirectly through value-added software.

Why does this matter? Well, this is an important difference that is often glossed over when comparing ATI's Avivo to Nvidia's Purevideo DVD playback quality enhancements. The decoder and how it's used is integral to making these quality enhancements happen.

What is Pulldown Detection, and why should I care?

Pretty much every feature film is shot at a shutter speed of 24 frames per second, or fps. That means each second of film is composed of 24 separate pictures.

Unfortunately, this does not sync up with the North American video standard, known as NTSC. NTSC calls for 30 frames per second.

In order to transfer 24 fps film to a 30fps NTSC DVD, a process known as "3:2 pulldown" is performed. Essentially, to stretch out the 24 frames of film to 30 frames, one frame is repeated for every five frames of film. That's where the 3:2 ratio comes in.

The unfortunate effect of 3:2 pulldown is a loss of video quality, characterized by unsettling "jaggies" and patterns that can be seen on moving objects. One of the main staples of a good DVD player is how well it detects 3:2 pulldown. If properly detected, the DVD player can reconstruct the original 24 fps source and eliminate the "jaggies" to deliver the original film's full frame of resolution.