The MPEG video on a DVD is stored in digital format, but it’s formatted for one of two mutually incompatible television systems: 525/60 (NTSC) or 625/50 (PAL/SECAM). Therefore, two kinds of DVDs exist: NTSC DVDs and PAL DVDs.

Some players only play NTSC discs; others play PAL and NTSC discs, depending on which region the owner lives in (refer to “What Are Regional Codes, Country Codes, or Zone Locks?”).

Almost all DVD players sold in PAL countries play both kinds of discs. These multistandard players partially convert NTSC to a 60 Hz PAL (4.43 NTSC) signal. The player uses the PAL 4.43 MHz color subcarrier encoding format but keeps the 525/60 NTSC scanning rate.

Most modern PAL TVs can handle this pseudo-PAL signal. A few multistandard PAL players output true 3.58 NTSC from NTSC discs, which requires an NTSC TV or a multistandard TV.

Some players have a switch to choose 60 Hz PAL or true NTSC output when playing NTSC discs. A few standards-converting PAL players convert output from an NTSC disc to standard PAL for older PAL TVs. Proper “on-the-fly” standards conversion requires expensive hardware to handle scaling, temporal conversion, and object motion analysis.

Because the quality of conversion in DVD players is poor, using 60 Hz PAL output with a compatible TV provides a better picture than converting from NTSC to PAL. (Sound is not affected by video conversion.)

The latest software tools such as Adobe After Effects and Canopus ProCoder do quite a good job of converting between PAL and NTSC at low cost, but they are only appropriate for the production environment (converting the video before it is encoded and put on the DVD).

Most NTSC players can’t play PAL discs. A small number of NTSC players (such as Apex and SMC) can convert PAL to NTSC. External converter boxes are also available, such as the Emerson EVC1595 (at $350).

Highquality converters are available from companies such as TenLab (www. tenlab.com) and Snell and Wilcox (www.snellwilcox.com). Many standardsconverting players can’t convert anamorphic widescreen video for 4:3 displays.

Three differences exist between discs intended for playback on different TV systems: picture dimensions and pixel aspect ratios (720 x 480 versus 720 x 576), the display frame rate (29.97 versus 25), and surround audio options (Dolby Digital versus MPEG audio).

Video from film is usually encoded at 24 frames per second but is preformatted for one of the two required display rates. Movies formatted for PAL display are usually sped up by 4 percent at playback, so the audio must be adjusted accordingly before being encoded.

All PAL DVD players can play Dolby Digital audio tracks, but not all NTSC players can play MPEG audio tracks. PAL and SECAM share the same scanning format, so discs are the same for both systems. The only difference is that SECAM players output the color signal in the format required by SECAM TVs.

Note that modern TVs in most SECAM countries can also read PAL signals, so you can use a player that only has PAL output. The only case in which you would need a player with SECAM output is for older SECAM-only TVs (and you’ll probably need a SECAM RF connection).

A producer can choose to put 525/60 NTSC video on one side of the disc and 625/50 PAL on the other. Most studios put Dolby Digital audio tracks on their PAL discs instead of MPEG audio tracks. Because of PAL’s higher resolution, the movie usually takes more space on the disc than the NTSC version.

Actually, three types of DVD players exist if you count computers. Most DVD PC software and hardware can play both NTSC and PAL video, as well as both Dolby Digital and MPEG audio. Some PCs can only display the converted video on the computer monitor, but others can output it as a video signal for a TV.

The bottom line is that NTSC discs (with Dolby Digital audio) play on over 95 percent of DVD systems worldwide. PAL discs play on very few players outside of PAL countries, irrespective of regions.