The Digital Versatile Disc is following us from the home and office right into the car. But the versatility that has made it so popular also leads to confusion. How can an average non-physicist keep track of everything it does? Here are some of the applications, compatibilities, and features you're likely - or in a few cases, unlikely - to hear about when shopping for a mobile DVD player.
DVD-Video 101While DVD is a disc, DVD-Video is a way of recording information on a disc. Designed primarily for movies, DVD-Video can hold more than 4 GB (gigabytes) per layer, or up to 17 GB on a disc with dual layers on each side. DVD-Video is a masterpiece of cross-industry cooperation with Toshiba and Warner Bros. as the lead inventors. To keep the peace, the format also incorporates technology from Sony and Philips (who threatened to introduce their own format before relenting) and many other companies.
DVD-Video contains both compressed video and compressed audio. The video format is MPEG-2, named for the Moving Picture Experts Group, which originated it. Audio can be encoded in either Dolby Digital from Dolby Labs, the folks who gave us Dolby theater and home surround formats, or DTS, from Digital Theater Systems, owned by Hollywood powers, including Universal Pictures and Steven Spielberg. DTS has a higher data rate and claims higher quality. Some complain that devoting more data to the audio side starves the video side, increasing blocky-looking video artifacts, but the problem won't be visible on a small mobile screen.
A common configuration on many DVD movie releases uses the eight (yes, eight) channels of Dolby Digital to provide both a 5.1-channel soundtrack (playable in the car as 4.0 or 4.1, sans center) and a two-channel mixdown for compatibility with pre-Dolby Digital equipment. The beauty of this is that the two-channel soundtrack can be played either in stereo or in the old analog Dolby Pro-Logic format which decodes Dolby Surround signals embedded in the two channels.
By the way, Dolby Pro-Logic is being replaced in home products by Dolby Pro Logic II. The new format is suitable for both surround-encoded and stereo sources. DPLII also has cool panning controls that adjust the sonic image from front to back or side to side.
Compact Disc CompatibilityDVDs and CDs are both 4.75-inch (not five-inch) discs. There the similarity ends. The spiraling pits on a DVD are much smaller than those on a CD and hold 13 times as much information. CD-Audio's simple PCM (pulse code modulation) method of recording is a far cry from the "lossy" MPEG-2 and Dolby Digital formats which discard repetitive or nonessential data to make DVD a far more efficient medium
Because DVDs and CDs differ in both their physical forms and data formats, CD compatibility is not part of the DVD-Video format specifications. However, consumers don't want to hear excuses. We want our DVD players to play CDs, period! That's why nearly all DVD players have been made CD-compatible, sometimes with two laser diodes on the same pickup.
Compatibility with recordable CD-R and CD-RW (rewritable) has taken longer. Early-generation home DVD players read CD-Rs inconsistently (some brands of blanks worked better than others); CD-RW compatibility was even rarer. Whereas the pits on a CD or a DVD are embedded into the disc, CD-R and -RW use a chemical process with lower reflectivity that's harder for the laser to read. However, consumers won't accept excuses here either, so compatibility is improving. To make sure, either look for Multi-Play certification from the Optical Storage Technology Association, or just try before you buy.