Full-size round labels designed to go on recordable DVDs generally work ok, but have been known to cause problems.

[1.45] What's the difference between Closed Captions and subtitles?

Closed Captions (CC) are a standardized method of encoding text into an NTSC television signal. The text can be displayed by a TV with a built-in decoder or by a separate decoder. All TVs larger than 13 inches sold in the US since 1993 have Closed Caption decoders. Closed Captions can be carried on DVD, videotape, broadcast TV, cable TV, and so on.

Even though the terms caption and subtitle have similar definitions, captions commonly refer to on-screen text specifically designed for hearing impaired viewers, while subtitles are straight transcriptions or translations of the dialogue. Captions are usually positioned below the person who is speaking, and they include descriptions of sounds and music. Closed captions are not visible until the viewer activates them. Open captions are always visible, such as subtitles on foreign videotapes.

Closed Captions on DVDs are carried in the MPEG-2 video stream and are automatically sent to the TV. You can't turn them on or off from the DVD player. Subtitles, on the other hand, are DVD subpictures, which are full-screen graphical overlays (see 3.4 for technical details). One of up to 32 subpicture tracks can be turned on to show text or graphics on top of the video. Subpictures can also be used to create captions. To differentiate from NTSC Closed Captions and from subtitles, captions created as subpictures are usually called "captions for the hearing impaired."

If this still confusing, just follow this advice: To see Closed Captions, use the CC button on the TV remote. To see subtitles or captions for the hearing impaired, use the subtitle button on the DVD remote or use the onscreen menu provided by the disc. Don't turn both on at once or they'll end up on top of each other. Keep in mind that not all DVDs have Closed Captions or subtitles. Also, a few DVD players do not reproduce Closed Captions at all.

See A Guide to DVD Subtitles and Captioning and the Caption FAQ for more about Closed Captions. Note that DVD does not support PAL Teletext, the much-improved European equivalent of Closed Captions.

[1.46] What do the "D" codes on region 2 DVDs mean?

Some non-U.S. discs from Warner, MGM, and Disney are marked with a distribution zone number. "D1" identifies a UK-only release. These often have English-only soundtracks with BBFC censoring. "D2" and "D3" identify European DVDs that are not sold in the UK and Ireland. These often contain uncut or less cut versions of films. "D4" identifies DVDs that are distributed throughout all of Europe (region 2) and Australia/New Zealand (region 4).

[1.47] What's firmware and why would I need to upgrade it?

DVD players are simple computers. Each one has a software program that controls how it plays discs. Since the software is stored on a chip, it's called firmware. Some players have flaws in their programming that cause problems playing certain DVDs. In order to correct the flaws, the player must be upgraded with a replacement firmware chip. This usually has to be done in a factory service center, although some players can be upgraded simply by inserting a CD. See 1.41 for more on compatibility problems.

[1.48] Are there discs to help me test, optimize, or show off my video system?

There are a few DVDs designed specifically for testing and optimizing video and audio playback. There are also some that demonstrate special features of DVD.

There are also a few movies that work especially well for demonstrating DVD's video and audio quality.

[2] DVD's relationship to other products and technologies

[2.1] Will DVD replace VCRs?

Not any time soon. Recordable DVD is for computer data only, not television video (see 1.14). It will take a while before the size of the market drives costs down to VCR levels. However, DVD has many advantages over VCRs, including fundamentally lower technology cost for hardware and disc production (which is appealing to manufacturers), so if DVD is a commercial success it might replace many VCRs in fifteen to twenty years.

[2.2] Will DVD replace CD-ROM?

Yes. Some CD-ROM drive manufacturers plan to cease CD-ROM drive production after a few years in favor of DVD-ROM drives. Because DVD-ROM drives can read CD-ROMs, there is a compatible forward migration path.

[2.3] Can CD-R writers create DVDs?

No. DVD uses a smaller wavelength of laser to allow smaller pits in tracks that are closer together. The DVD laser must also focus more tightly and at a different level. In fact, a disc made on a current CD-R writer may not be readable by a DVD-ROM drive (see 2.4.3). It's unlikely there will be "upgrades" to convert CD-R drives to DVD-R, since this would probably cost more than purchasing a new DVD-R drive.

[2.4] Is CD compatible with DVD?

This is actually many questions with many answers, covered in the following sections.
[Note the differentiation between DVD (general case) and DVD-ROM (computer data).]

[2.4.1] Is CD audio (CD-DA) compatible with DVD?

Yes. All DVD players and drives will read audio CDs (Red Book). This is not actually required by the DVD spec, but so far all manufacturers have made their DVD hardware read CDs.

On the other hand, you can't play a DVD in a CD player. (The pits are smaller, the tracks are closer together, the data layer is a different distance from the surface, the modulation is different, the error correction coding is new, etc.) Also, you can't put CD audio data onto a DVD and have it play in DVD players. (Red Book audio frames are different than DVD data sectors.)

[2.4.2] Is CD-ROM compatible with DVD-ROM?

Yes. All DVD-ROM drives will read CD-ROMs (Yellow Book). Software on a CD-ROM will run fine in a DVD-ROM system.

However, DVD-ROMs are not readable by CD-ROM drives.

[2.4.3] Is CD-R compatible with DVD?

Sometimes. The problem is that CD-Rs (Orange Book Part II) are "invisible" to DVD laser wavelength because the dye used in CD-Rs doesn't reflect the beam. Some first-generation DVD-ROM drives and many DVD players can't read CD-Rs. The formulation of dye used by different CD-R manufacturers also affects readability. That is, some brands of CD-R discs have better reflectivity at DVD laser wavelength, but even these don't reliably work in all players.

The common solution is for the DVD player or drive to use two lasers at different wavelengths: one for reading DVDs and the other for reading CDs and CD-Rs. Variations on the theme include Sony's "dual discrete optical pickup" with switchable pickup assemblies with separate optics, Sony's dual-wavelength laser (to be initially deployed on Playstation 2), Samsung's "annular masked objective lens" with a shared optical path, Toshiba's similar shared optical path using an objective lens masked with a coating that's transparent only to 650-nm light, Hitachi's switchable objective lens assembly, and Matsushita's holographic dual-focus lens. The MultiRead logo guarantees compatibility with CD-R and CD-RW media, but unfortunately, few manufacturers are using it.

Bottom line: If you want a DVD player that can read CD-R discs, look for a "dual laser" or "dual optics" feature.

An effort to develop CD-R "Type II" media compatible with both CD and DVD wavelengths was abandoned.

DVD-ROM drives can't record on CD-R or any other media. There are a few combination DVD-ROM/CD-RW drives that can write to CD-R and CD-RW. Current writable DVD drives (see 4.3) can't record on CD-R or CD-RW, although future versions will.

[2.4.4] Is CD-RW compatible with DVD?

Usually. CD-Rewritable (Orange Book Part III) has a smaller reflectivity difference, requiring new automatic-gain-control (AGC) circuitry in CD-ROM drives and CD players. CD-RW discs can't be read by most existing CD-ROM drives and CD players. The "MultiRead" standard addresses this, and some DVD manufacturers have suggested they will support it. The optical circuitry in even first-generation DVD-ROM drives and DVD players is usually able to read CD-RW discs, since CD-RW does not have the "invisibility" problem of CD-R (see 2.4.3).

Current writable DVD drives (see 4.3) can't record on CD-RW, although future versions will.

[2.4.5] Is Video CD compatible with DVD?

Sometimes. It's not required by the DVD spec, but it's trivial to support the Video CD (White Book) standard since any MPEG-2 decoder can also decode MPEG-1 from a Video CD. About two thirds of DVD players can play Video CDs. Panasonic, RCA, Samsung, and Sony models play Video CDs. Japanese Pioneer models play Video CDs but American models older than the DVL-909 don't. Toshiba players older than models 2100, 3107, and 3108 don't play Video CDs.

VCD resolution is 352x288 for PAL and 352x240 for NTSC. The way most DVD players and Video CD players deal with the difference is to chop off the extra lines or add blank lines. When playing PAL VCDs, the Panasonic and RCA NTSC players apparently cut 48 lines (17%) off the bottom. The Sony NTSC players scale all 288 lines to fit.

Because PAL VCDs are encoded for 25 fps playback of 24 fps film, there is usually a 4% speedup. Playing time is shorter, and the audio is shifted up in pitch unless it was digitally processed before encoding to shift the pitch back to normal. This also happens with PAL DVDs (see 1.19).

All DVD-ROM computers can play Video CDs (with the right software).

Standard VCD players can't play DVDs.

Note: Many Asian VCDs achieve two soundtracks by putting one language on the left channel and another on the right. The two channels are mixed together into babel on a stereo system unless you adjust the balance or disconnect one input to get only one channel.

For more on Video CD, see Glenn Sanderse's Video CD FAQ at CDPage, or Russil Wvong's Video CD FAQ.

[2.4.6] Is Super Video CD compatible with DVD?

Not generally. Super Video CD (SVCD) is an enhancement to Video CD that was developed by a Chinese government-backed committee of manufacturers and researchers, partly to sidestep DVD technology royalties and partly to create pressure for lower DVD player and disc prices in China. The final SVCD spec was announced in September 1998, winning out over C-Cube's China Video CD (CVD) and HQ-VCD (from the developers of the original Video CD). In terms of video and audio quality, SVCD is in between Video CD and DVD, using a 2x CD drive to support 2.2 Mbps VBR MPEG-2 video (at 480x480 (NSTC) or 480x576 (PAL) resolution) and 2-channel MPEG-2 Layer II audio. As with DVD, it can overlay graphics for subtitles. It's technically easy to make a DVD-Video player compatible with SVCD, but it's being done mostly on Asian DVD player models. The Philip's DVD170 player can be upgraded (using a special disc) to play SVCD discs.

SVCD players can't play DVDs, since the players are based on CD drives.

See Jukka Aho's Super Video CD Overview and Super Video CD FAQ for more info.


[2.4.7] Is Photo CD compatible with DVD?

Not generally. Since Photo CDs are usually on CD-R media, they suffer from the CD-R problem (see 2.4.3). That aside, DVD players could support Photo CD with a few extra chips and a license from Kodak. No one has announced such a player. Most DVD-ROM drives will read Photo CDs (if they read CD-Rs) since it's trivial to support the XA and Orange Book multisession standards. The more important question is, "Does the OS or application support Photo CD?" but that's beyond the scope of this FAQ.

[2.4.8] Is CD-i compatible with DVD?

In general, no. Current DVD players do not play CD-i (Green Book) discs. Philips once announced that it would make a DVD player that supported CD-i, but it has yet to appear. Some people expect Philips to create a "DVD-i" format in an attempt to breathe a little more life into CD-i (and recover a bit more of the billion or so dollars they invested in it). A DVD-ROM PC with a CD-i card should be able to play CD-i discs.

There are also "CD-i movies" that use the CD-i Digital Video format that was the precursor to Video CD. Early CD-i DV discs won't play on DVD players or VCD players, but newer CD-i movies, which use standard VCD format, will play on any player that can play VCDs (see 2.4.5).

See Jorg Kennis' CD-i FAQ for more information on CD-i.

[2.4.9] Is Enhanced CD compatible with DVD?

Yes. DVD players will play music from Enhanced Music CDs (Blue Book, CD Plus, CD Extra), and DVD-ROM drives will play music and read data from Enhanced CDs. Older ECD formats such as mixed mode and track zero (pregap, hidden track) should also be compatible, but there is a problem with Microsoft and other CD/DVD-ROM drivers skipping track zero.

[2.4.10] Is CD+G compatible with DVD?

Only the Pioneer DVL-9 player and Pioneer karaoke DVD models DV-K800 and DVK-1000 are known to support CD+G. Most other DVD-V players probably won't support this mostly obsolete format. All DVD-ROM drives support CD+G, but special software is required to make use of it.

[2.4.11] Is CDV compatible with DVD?

Sort of. CDV, sometimes called Video Single, is actually a weird combination of CD and laserdisc. Part of the disc contains 20 minutes of digital audio playable on any CD or DVD player. The other part contains 5 minutes of analog video and digital audio in laserdisc format, playable only on a CDV-compatible laserdisc player. Pioneer's combination DVD/laserdisc players are the only DVD players that can play CDVs.

Standard laserdisc/CDV players can't play DVDs. (See 2.5 for more LD info.)

[2.4.12] Is MP3 compatible with DVD?

Mostly no. MP3 is the MPEG-1 Layer 3 audio compression format. (MP3 is not MPEG-3, which doesn't exist.) The DVD-Video spec allows only Layer 2 for MPEG audio. MP3 can be played on computers with a DVD-ROM drive. A few DVD players (Apex/REC/VDDV, DiViDo, Euro Asia/Smart, I-Jam, Lasonic, Nintaus, Raite [AV Phile/Hoyo/KiSS/Monica/Monyka/Tokai/Yamakawa], Revoy, Sampo, Shinco) can play MP3 CDs. (See 6.2 for company Web sites.)

[2.4.13] Is HDCD compatible with DVD?

Yes. Pacific Microsonics' HDCD (high-definition compatible digital) is an encoding process that enhances audio CDs so that they play normally in standard CD and DVD players (and allegedly sound better than normal CDs) yet produce an extra 4 bits of precision (20 bits instead of 16) when played on CD and DVD players equipped with HDCD decoders.

[2.5] Is laserdisc compatible with DVD?

No. Standard DVD players will not play laserdiscs, and you can't play a DVD disc on any standard laserdisc player. (Laserdisc uses analog video, DVD uses digital video; they are very different formats.)

However, Pioneer produces combo players that play laserdiscs and DVDs (and also CDVs and audio CDs). Denon and Samsung are rumored to have LD/DVD players in the works also.

[2.6] Will DVD replace laserdisc?

When this question was first entered in the FAQ, before DVD was even available, people wondered if DVD would replace laserdisc (and some argued it never would -- that DVD would fail and it's adherents would come groveling back to laserdisc). After DVD was released, it became clear that it had doomed laserdisc to quick obscurity. Pioneer Entertainment, the long-time champion of laserdisc, abandoned it in June of 1999. This was sooner than even Pioneer thought possible, (in September 1998, Pioneer's president Kaneo Ito said the company expected laserdisc products to be in the market for another one-and-a-half to two years).

Laserdisc still fills important niches in education and training, but is fading very quickly as an entertainment format. Existing players and discs will still be around for a very long time, and new discs are still being produced, since laserdisc has become well established over 20 years as a videophile format. There are over 9,000 laserdisc titles in the US and a total of over 35,000 titles worldwide that can be played on over 7 million laserdisc players. It will take DVD several years to reach this level, and even then there's no reason for laserdisc player owners to stop buying or playing laserdiscs, especially rare titles that may not appear on DVD for a long while if ever. One bright point is that laserdiscs (especially used discs) can now be had at bargain prices.

[2.7] How does DVD compare to laserdisc?

For more laserdisc info, see Leopold's FAQ at <>, and Bob Niland's FAQs and overview at <> (overview reprinted from Widescreen Review magazine).

[2.8] Can I modify or upgrade my laserdisc player to play DVD?

It's not likely. DVD circuitry is completely different, the pickup laser is a different wavelength, the tracking control is more precise, etc. No hardware upgrades have been announced, and in any case they would probably be more expensive than buying a DVD player to put next to the laserdisc player.

[2.9] Does DVD support HDTV (DTV)? Will HDTV make DVD obsolete?

Short answers: Partially. No.

First, some quick definitions: HDTV (high-definition TV) encompasses both analog and digital televisions that have a 16:9 aspect ratio and approximately 5 times the resolution of standard TV (double vertical, double horizontal, wider aspect). DTV (digital TV) applies to digital broadcasts in general and to the U.S. ATSC standard in specific. The ATSC standard includes both standard-definition (SD) and high-definition (HD) digital formats. The notation H/DTV is often used to specifically refer to high-definition digital TV.

In December of 1996 the FCC approved the U.S. DTV standard. HDTVs became available in late 1998, but they are very expensive and won't become widespread for many years. DVD will look better on HDTVs but it won't provide the highest resolutions.

DVD-Video does not directly support HDTV. No digital HDTV standards were finalized when DVD was developed. In order to be compatible with existing televisions, DVD's MPEG-2 video resolutions and frame rates are closely tied to NTSC and PAL/SECAM video formats (see 1.19). DVD does use the same 16:9 aspect ratio of HDTV and the Dolby Digital audio format of U.S. DTV.

HDTV in the US is part of the ATSC DTV format. The resolution and frame rates of DTV in the US generally correspond to the ATSC recommendations for SD (640x480 and 704x480 at 24p, 30p, 60p, 60i) and HD (1280x720 at 24p, 20p, and 60p; 1920x1080 at 24p, 30p and 60i). (24p means 24 progressive frames/sec, 60i means 60 interlaced fields/sec [30 frames/sec].) The current DVD-Video spec covers all of SD except 60p. It's expected that future DVD players will output digital video signals from existing discs in SDTV formats. The HD formats are 2.7 and 6 times the resolution of DVD, and the 60p version is twice the frame rate. The ITU-R is working on BT.709 HDTV standards of 1125/60 (1920x1035/30) (same as SMPTE 240M, similar to Japan's analog MUSE HDTV) and 1250/50 (1920x1152/25) which may be used in Europe. The latter is 5.3 times the resolution of DVD's 720x576/25 format. HD maximum data rate is usually 19.4 Mbps, almost twice the maximum DVD-Video data rate. In other words, DVD-Video does not currently support HDTV video content.

HDTV will not make DVD obsolete. Those who postpone purchasing a DVD player because of HDTV are in for a long wait. HDTV became available in late 1998 at very high prices (about $5000 and up). It will take many years before even a small percentage of homes have HDTV sets. CEA expects 10 percent of U.S. households to have HDTV in 2003, 20 percent by 2005, and 30 percent by 2006.

HDTV sets include analog video connectors (composite, s-video, and component) that will work with all DVD players and other existing video equipment such as VCRs. Existing DVD players and discs will work perfectly with HDTV sets, and will provide a much better picture than any other prerecorded consumer video format, especially once new progressive-scan players become available. Since the cheapest route to HDTV reception will be HDTV converters for existing TV sets, HDTV for many viewers will look no better than DVD.

At some point, HDTV displays will support component digital video connections (YCbCr) and digital data connections (FireWire/IEEE 1394). The digital connections will provide the best possible reproduction of DVD-Video, especially in widescreen mode. Once DVD players have digital outputs, they may be usable as "transports" which output any kind of A/V data (even formats developed after the player was built) to any sort of external display or converter.

The interesting thing many people don't realize is that DTV is happening soonest, fastest, and cheapest on PCs. A year before any consumer DTV sets came out you could buy a DVD PC with a 34" VGA monitor and get gorgeous progressive-scan movies for under $3000. The quality of a good DVD PC connected to a data-grade video projector beats $30,000 line-doubler systems. (See NetTV, BroadbandMagic, and Digital Connection for product examples. Video projectors are available from Barco, Dwin, Electrohome, Faroudja, InFocus, Projectavision, Runco, Sharp, Sony, Vidikron, and others.)

Eventually the DVD-Video format will be upgraded to an "HD-DVD" format. See 2.12.

[2.10] What was Divx?

Note: There is a computer-based "DVD ripper" that was named after the original Divx in an annoying little joke that has caused untold confusion. See 4.8 for more info.

Depending on whom you ask, Divx (once known as ZoomTV) was either an insidious evil scheme for greedy studios to control what you see in your own living room or an innovative approach to video rental with cheap discs you could get almost anywhere and keep for later viewings. On June 16, 1999, less than a year after initial product trials, Digital Video Express announced that it was closing down. Divx did not confuse or delay development of the DVD market nearly as much as many people predicted (including yours truly). In fact, it probably helped by stimulating Internet rental companies to provide better services and prices, by encouraging manufacturers to offer more free discs with player purchases, and by motivating studios to develop rental programs.

The company offered $100 rebate coupons to all owners of Divx players. This made the players a good deal, since they can play open DVDs just as well as other low-end players that cost more. The Divx billing computer will continue to operate normally until June 30th, 2001, after which all Divx discs will presumably become unplayable. Divx discs can no longer be upgraded to unlimited play.

Developed by Circuit City and a Hollywood law firm, Divx was supported by Disney (Buena Vista), Twentieth Century Fox, Paramount, Universal, MGM, and DreamWorks SKG, all of which also released discs in "open DVD" format, since the Divx agreement was non-exclusive. Harman/Kardon, JVC, Kenwood, Matsushita (Panasonic), Pioneer, Thomson (RCA/Proscan/GE), and Zenith announced Divx players, though some never came to market. (Divx models are Panasonic X410, Proscan PS8680Z, RCA RC5230Z and RC5231Z, and Zenith DVX2100.) The studios and hardware makers supporting Divx were given incentives in the form of guaranteed licensing payments totaling over $110 million. Divx discs were manufactured by Nimbus, Panasonic, and Pioneer. Circuit City lost over $114 million (after tax writeoffs) on Divx.

Divx was a pay-per-viewing-period variation of DVD. Divx discs sold for $4.50. Once inserted into a Divx player the disc would play normally (allowing the viewer to pause, rewind, even put in another disc before finishing the first disc) for the next 48 hours, after which the "owner" had to pay $3.25 to unlock it for another 48 hours. A Divx DVD player, which cost about $100 more than a regular player, had to be hooked up to a phone line so it could call an 800 number for about 20 seconds during the night once each month (or after playing 10 or so discs) to upload billing information. Most Divx discs could be converted to DivxSilver status by paying an additional fee (usually $20) to allow unlimited plays on a single account (as of Dec 1998, 85% of Divx discs were convertible). Unlimited-playback DivxGold discs were announced but never produced. Divx players can also play regular DVD discs, but Divx discs do not play in standard DVD players. Divx discs are serialized (with a barcode in the standard Burst Cutting Area) and in addition to normal DVD copy protection (see 1.11) they employ watermarking of the video, modified channel modulation, and triple DES encryption (three 56-bit keys) of serial communications. Divx technology never worked on PCs, which undoubtedly contributed to its demise. Because of the DES encryption, Divx technology may not have been allowed outside the U.S.

Divx was originally announced for summer 1998 release. Limited trials began June 8, 1998 in San Francisco, CA and Richmond, VA. The only available player was from Zenith (which at the time was in Chapter 11 bankruptcy), and the promised 150 movies had dwindled to 14. The limited nationwide rollout (with one Zenith player model and 150 movies in 190 stores) began on September 25, 1998. By the end of 1998 about 87,000 Divx players (from four models available) and 535,000 Divx discs were sold (from about 300 titles available). The company apparently counted the five discs bundled with each player, which means only 100,000 additional discs were sold. By March 1999, 420 Divx titles were available (compared to over 3,500 open DVD titles).

For more information see the Divx Owner's Association.

Advantages of Divx:

Disadvantages of Divx :

[2.11] How can I record from DVD to videotape?

Why in the world would you want to degrade DVD's beautiful digital picture by copying it to analog tape? Especially since you lose the interactive menus and other nice features.

If you really want to do this, hook the audio/video outputs of the DVD player to the audio/video inputs of your VCR, then record the disc to tape. You'll discover that most of the time the resulting tape is garbled and unwatchable. This is because of the Macrovision feature designed to prevent you from doing this. See 1.11.

[2.12] Will high-definition DVD or 720p DVD make current players and discs obsolete?

Not for a long time. HD-DVD "technology demonstrations" being made by various companies do not mean that HD-DVD is around the corner (the demonstrations mean only that companies are busy jockeying for technology and patent positions in developing the future DVD format). Consider that U.S. HDTV was anticipated to be available in 1989, yet was not finalized until 1996, and did not appear until 1998. And has it made your current TV obsolete yet?

HD-DVD (HD stands for both high-density and high-definition) may be available in 2003 at the very earliest, though 2006 is more likely. It will use blue or violet lasers to read smaller pits, increasing data capacity to around 20 GB per layer. MPEG-2 Progressive Profile--or perhaps another format such as H.263--will probably be used to encode the video. All ATSC and DVB formats will be supported, possibly with the addition of 1080p24. HD-DVD players will play current DVD discs and will make them look even better (with progressive-scan video and picture processing), but new HD-DVD discs won't be playable in older DVD players (unless one side is HD and the other standard DVD).

Ironically, computers will support HDTV before settop players do, since 2x DVD-ROM drives coupled with appropriate playback and display hardware meet the 19 Mbps data rate needed for HDTV. This has led to various "720p DVD" projects, which use the existing DVD format to store video in 1280x720 resolution at 24 progressive frames per second. It's possible that 720p DVDs can be made compatible with existing players (which would only play the 480-line line data).

Note: The term HDVD has already been taken for "high-density volumetric display."

Some have speculated that a "double-headed" player reading both sides of the disc at the same time could double the data rate or provide an enhancement stream for applications such as HDTV. This is currently impossible since the track spirals go in opposite directions (unless all four layers are used). The DVD spec would have to be changed to allow reverse spirals on layer 0. Even then, keeping both sides in sync, especially with MPEG-2's variable bit rate, would require independently tracking heads, precise track and pit spacing, and a larger, more sophisticated track buffer. Another option would be to use two heads to read both layers of one side simultaneously. This is technically feasible but has no advantage over reading one layer twice as fast, which is simpler and cheaper.

See 2.9 for more information about HDTV and DVD.

[2.13] What effect will FMD have on DVD?

Who knows? So far Constellation 3D's FMD (fluorescent multilayer disc) isn't out of the lab. You can be sure only that the reports of FMD causing the early death of DVD are wildly exaggerated and not founded in reality.

Fluorescent multilayer technology, which can be used in cards or discs, aims a laser at fluorescent recording material, causing it to emit light. Since it doesn't depend on reflected laser light, it's possible to create many data layers (C3D has prototyped 50 layers in its lab). It can use the same 650 nm laser as DVD, so FMD drives could be made to read DVDs. In June 2000, C3D announced a program to make FMDs with 25 GB per side that would be readable by DVD drives with a "minor and inexpensive modification."

FMD is a new technology, with no track record, supported by one small company. DVD is based on decades of optical storage technology development by dozens of companies. It's possible that FMD could become established in few years, but DVD is already so entrenched that FMD drives will have to read DVDs in order to succeed. So there is little worry of DVD becoming obsolete any time soon. Perhaps FMD will be the third generation of the DVD format, following the high-density blue-laser version currently under development (see 2.12)

[2.14] How does MPEG-4 affect DVD?

MPEG-4 is a video encoding standard designed primarily for low-data rate streaming video, although it's actually more efficient than MPEG-2 at DVD and HDTV data rates. MPEG-4 also provides for advanced multimedia with media objects, but most implementations only support simple video (Simple Visual Profile). 

DVD uses MPEG-2 video encoding (see 3.4 for details). Standard DVD players don't recognize the MPEG-4 video format. MPEG-4 files can be stored on DVD-ROM for use on computers. For example, Divx;-) uses MPEG-4 (see 4.8).

It's possible that MPEG-4 will be used in a future, high-definition version of DVD. It's also possible that a similar format such as H.263 will be used for the next generation of DVD. In any case, it will probably not appear before 2004 at the earliest.

For more about MPEG, see Tristan's site and the MPEG home page.

[2.15] What's WebDVD?

WebDVD is the simple concept of combining DVD content with Internet technology. It combines the best of DVD (fast access to high-quality video, audio, and data) with the best of the Internet (interactivity, dynamic updates, and communication). In general, WebDVD refers to enhancing a DVD with HTML pages and links, or enhancing a Web site with content from a local DVD drive. WebDVD is not a trademarked term of AOL-Warner, Microsoft, or any other company. Variations on the WebDVD concept are known as iDVD, eDVD, Connected DVD, and so on. It's not a new idea --it's been done with CD-ROM for years-- but the differences with DVD are that the quality of the audio and video are finally better than TV, and the discs can be played in low-cost settop players. Almost all WebDVD implementations are currently for PCs, but new players such as Nuon-based models are adding WebDVD features.

Most major authoring systems (see 5.4) include rudimentary tools for adding HTML enhancements to DVD. For fancier WebDVD development there are a variety of tools; see 4.9.

For more on WebDVD, see Phil DeLancie's EMedia article. Good examples of WebDVD sites are Mars: The Red Planet, Stargaze, and DVD Demystified. The authors of these sites (Ralph LaBarge and Jim Taylor) encourage you to copy their code as a starting place for your own WebDVD creations.

[3] DVD technical details

[3.1] What are the outputs of a DVD player?

Video outputs

Most DVD players have the following video output connections, which can carry an NTSC, PAL, or SECAM signal.

Some players may have additional video connections:

Most of the DVD players with component video outputs use YUV (Y'PbPr), which is incompatible with RGB equipment. European players with SCART connectors have RGBS outputs. YUV to RGB transcoders are rumored to be available for $200-$300, but seem hard to track down. A $700 converter is available from avscience, and $900 converter, the CVC 100, is available from Extron. Converters are also available from Altinex, Kramer, Monster Cable, and others. For progressive scan you need a converter that can handle 31.5 kHz signals. Converters from s-video are also an option (Markertek Video Supply, 800-522-2025).

Note: The correct term for analog color-difference output is Y'Pb'Pr', not Y'Cb'Cr' (which is digital, not analog). To simplify things, this FAQ sometimes uses the term YUV in the generic sense to refer to analog color difference signals.

No consumer DVD players have yet been announced with digital video outputs, but digital output will soon be available using FireWire (IEEE 1394) connectors. There are specialty players from Function Communications, Theta Digital, and Vigatec with SDI (serial digital interface) output, but they connect only to high-end or production equipment.

Audio outputs

Most DVD players have the following audio output connections.

Some players may have additional audio connections:

Some players and receivers support only S/P DIF or only Toslink. If your player and receiver don't match, you'll need a converter such as the Audio Authority 977 Midiman C02, COP 1, or POF.

Some players can output 96/24 PCM audio using a non-standard variation of IEC-958 running at 6.2 MHz (6.144 Mbps) instead of the normal limit of 3.1 MHz. Note: The CSS license does not allow digital PCM output of CSS-protected material at 96 kHz. The player must downsample to 48 kHz.

[3.2] How do I hook up a DVD player?

It depends on your audio/video system and your DVD player. Most DVD players have 2 or 3 video hookup options and 3 audio hookup options. Choose the output format with the best quality (indicated below) that is supported by your video and audio systems. See 3.1 for output connector details.

If you want to hook multiple devices (DVD player, VCR, cable/satellite box, WebTV, etc.) to a single TV, you need a TV with multiple inputs, or an A/V receiver (to switch between video sources via remote control), or a manual audio/video switchbox (~$30 at electronics suppliers such as Comtrad). If you plan on getting an A/V receiver, make sure it can switch the video format you want to use (component or s-video).

Video hookup

Warning: If you connect your DVD player to a VCR and then to your TV, you may have problems with discs that enable the player's Macrovision circuit. See 3.2.1.

Warning: Some video projectors don't recognize the 4.43 NTSC signal from NTSC discs in PAL players (see 1.19). They see the 60Hz scanning frequency and switch to NSTC even though the color subcarrier is in PAL format.

Note: Most DVD players support widescreen signaling, which tells a widescreen display what the aspect ratio is so that it can automatically adjust. One standard (ITU-R BT.1119, used mostly in Europe) includes information in a video scanline. Another standard, for Y/C connectors, adds a 5V DC signal to the chroma line to designate a widescreen signal. Unfortunately, some switchers and amps throw away the DC component instead of passing it on to the TV.

For more information on conversions between formats, see the amazing Notes on Video Conversion from the Sci.Electronics.Repair FAQ.

Audio hookup

Note: All DVD players have a built-in 2-channel Dolby Digital (AC-3) decoder. Some can also decode MPEG audio or DTS audio. The decoder translates multichannel audio into PCM audio. This is fed to the digital output and also converted to analog for standard audio output. See 3.6.3 for more explanation.

[3.2.1] Will I have problems connecting my VCR between my TV and my DVD player?

It's not a good idea to route the video from your DVD player through your VCR. Most movies use Macrovision protection (see 1.11), which affects VCRs and causes problems such as a repeated darkening and lightening of the picture. If your TV doesn't have a direct video input, you may need a separate RF converter (see 3.2). Or better yet, get a new TV with s-video inputs.

You may also have problems with a TV/VCR combo, since many of them route the video input through the VCR circuitry. The only solution is to get a box to strip Macrovision (see 1.11). 

[3.2.2] Why is the audio or video bad?

The number one cause of bad video is a poorly adjusted TV. The high fidelity of DVD video demands much more from the display. Turn the sharpness and brightness down. See 1.3 for more information. For technical details of TV calibration, see Anthony Haukap's FAQ: How To Adjust a TV.

If you get audio hum or noisy video, it's probably caused by interference or a ground loop. Try a shorter cable. Make sure the cable is adequately shielded. Try turning off all equipment except the pieces you are testing. Try moving things farther apart. Try plugging into a different circuit. Wrap your entire house in tinfoil. Make sure all equipment is plugged into the same outlet. For more on ground loops, see <>.

[3.3] What are the sizes and capacities of DVD?

There are many variations on the DVD theme. There are two physical sizes: 12 cm (4.7 inches) and 8 cm (3.1 inches), both 1.2 mm thick, made of two 0.6mm substrates glued together. These are the same form factors as CD. A DVD disc can be single-sided or double-sided. Each side can have one or two layers of data. The amount of video a disc can hold depends on how much audio accompanies it and how heavily the video and audio are compressed. The oft-quoted figure of 133 minutes is apocryphal: a DVD with only one audio track easily holds over 160 minutes, and a single layer can actually hold up to 9 hours of video and audio if it's compressed to VHS quality.

At a rough average rate of 4.7 Mbps (3.5 Mbps for video, 1.2 Mbps for three 5.1-channel soundtracks), a single-layer DVD can hold a little over two hours. A two-hour movie with two soundtracks can average 5.2 Mbps (with 4 Mbps for video). A dual-layer disc can hold a two-hour movie at an average of 9.5 Mbps (close to the 10.08 Mbps limit).

A DVD-Video disc containing mostly audio can play for 13 hours (24 hours with dual layers) using 48/16 PCM (slightly better than CD quality). It can play 160 hours of audio (or a whopping 295 hours with dual layers) using Dolby Digital 64 kbps compression of monophonic audio, which is perfect for audio books.

Capacities of DVD:

For reference, a CD-ROM holds about 650 megabytes, which is 0.64 gigabytes or 0.68 billion bytes. In the list below, SS/DS means single-/double-sided, SL/DL/ML means single-/dual-/mixed-layer (mixed means single layer on one side, double layer on the other side), gig means gigabytes (2^30), BB means billions of bytes (10^9). See note about giga vs. billion in section 7.2.

DVD-5 (12 cm, SS/SL) 4.37 gig (4.70 BB) of data, over 2 hours of video
DVD-9 (12 cm, SS/DL) 7.95 gig (8.54 BB), about 4 hours
DVD-10 (12 cm, DS/SL) 8.74 gig (9.40 BB), about 4.5 hours
DVD-14 (12 cm, DS/ML) 12.32 gig (13.24 BB), about 6.5 hours
DVD-18 (12 cm, DS/DL) 15.90 gig (17.08 BB), over 8 hours
DVD-1 (8 cm, SS/SL) 1.36 gig (1.46 BB), about half an hour
DVD-2 (8 cm, SS/DL) 2.47 gig (2.66 BB), about 1.3 hours
DVD-3 (8 cm, DS/SL) 2.72 gig (2.92 BB), about 1.4 hours
DVD-4 (8 cm, DS/DL) 4.95 gig (5.32 BB), about 2.5 hours
DVD-R 1.0 (12 cm, SS/SL) 3.68 gig (3.95 BB)
DVD-R 2.0 (12 cm, SS/SL) 4.37 gig (4.70 BB); 8.75 gig for rare DS discs
DVD-RW 2.0 (12 cm, SS/SL) 4.37 gig (4.70 BB); 8.75 gig for rare DS discs
DVD-RAM 1.0 (12 cm, SS/SL) 2.40 gig (2.58 BB)
DVD-RAM 1.0 (12 cm, DS/SL)  4.80 gig (5.16 BB)
DVD-RAM 2.0 (12 cm, SS/SL) 4.37 gig (4.70 BB)
DVD-RAM 2.0 (12 cm, DS/SL) 8.75 gig (9.40 BB)
DVD-RAM 2.0 (8 cm, SS/SL) 1.36 gig (1.46 BB)
DVD-RAM 2.0 (8 cm, DS/SL) 2.47 gig (2.65 BB)
CD-ROM (12 cm, SS/SL) 0.635 gig (0.650 BB)
CD-ROM (8 cm, SS/SL) 0.180 gig (0.194 BB)
DDCD-ROM (12 cm, SS/SL) 1.270 gig (1.364 BB)
DDCD-ROM (8 cm, SS/SL) 0.360 gig (0.387 BB)

Tip: It takes about two gigabytes to store one hour of average video.

The increase in capacity from CD-ROM is due to: 1) smaller pit length (~2.08x), 2) tighter tracks (~2.16x), 3) slightly larger data area (~1.02x), 4) more efficient channel bit modulation (~1.06x), 5) more efficient error correction (~1.32x), 6) less sector overhead (~1.06x). Total increase for a single layer is about 7 times a standard CD-ROM. There's a slightly different explanation at <>.

The capacity of a dual-layer disc is slightly less than double that of a single-layer disc. The laser has to read "through" the outer layer to the inner layer (a distance of 20 to 70 microns). To reduce inter-layer crosstalk, the minimum pit length of both layers is increased from 0.4 um to 0.44 um. To compensate, the reference scanning velocity is slightly faster -- 3.84 m/s, as opposed to 3.49 m/s for single layer discs. Longer pits, spaced farther apart, are easier to read correctly and are less susceptible to jitter. The increased length means fewer pits per revolution, which results in reduced capacity per layer.

Note: Older versions of Windows that use FAT16 instead of UDF, FAT32, or NTFS to read a DVD may run into problems with the 4 gigabyte volume size limit. FAT16 also has a 2 gigabyte file size limit, while FAT32 has a 4 gigabyte file size limit. (NTFS has a 2 terabyte limit, so we're ok there for a while.)

See 4.3 for details of writable DVD. More info on disc specifications and manufacturing can be found at Disctronics, Cinram. Panasonic, Technicolor, and other disc replicator sites. 

[3.3.1] When will double-sided, dual-layer discs (DVD-18) be available?

The first commercial DVD-18 title, The Stand, was released in October 1999. It will still take a while for these super-size discs to become common. A DVD-18 requires a completely different way of creating two layers. A single-sided, dual-layer disc (DVD-9) is produced by putting one data layer on each substrate and gluing the halves together with transparent adhesive so that the pickup laser can read both layers from one side. But in order to get four layers, each substrate needs to hold two. This requires stamping a second data layer on top of the first, a much more complicated prospect. Even after new equipment is developed and installed in production lines, the yield (number of usable discs compared to bad discs) will be quite low until the process is fine tuned.

WAMO and others continue to announce progress with DVD-18 processes, but given how long it took for production of dual-layer, single-sided discs to become practical, it will take even longer before the yields of DS/DL discs can meet the replication demands of mainstream movie distribution, especially since low yields mean higher replication costs. In the interim we'll see DVD-14s (two layers on one side, one layer on the other side), since they're a little easier to produce.

(My prediction in this FAQ, as of December 1998, was that we wouldn't see commercial DVD-18 discs until fall 1999, in spite of many rumors that they would appear sooner.)

[3.4] What are the video details?

DVD-Video is an application of DVD-ROM. DVD-Video is also an application of MPEG-2. This means the DVD format defines subsets of these standards to be applied in practice as DVD-Video. DVD-ROM can contain any desired digital information, but DVD-Video is limited to certain data types designed for television reproduction.

A disc has one track (stream) of MPEG-2 constant bit rate (CBR) or variable bit rate (VBR) compressed digital video. A restricted version of MPEG-2 Main Profile at Main Level (MP@ML) is used. SP@ML is also supported. MPEG-1 CBR and VBR video is also allowed. 525/60 (NTSC, 29.97 interlaced frames/sec) and 625/50 (PAL, 25 interlaced frames/sec) video display systems are expressly supported. Coded frame rates of 24 fps progressive from film, 25 fps interlaced from PAL video, and 29.97 fps interlaced from NTSC video are typical. MPEG-2 progressive_sequence is not allowed, but interlaced sequences can contain progressive pictures and progressive macroblocks. In the case of 24 fps source, the encoder embeds MPEG-2 repeat_first_field flags into the video stream to make the decoder either perform 2-3 pulldown for 60Hz (59.94) displays or 2-2 pulldown (with resulting 4% speedup) for 50Hz displays. In other words, the player doesn't really "know" what the encoded rate is, it simply follows the MPEG-2 encoder's instructions to produce the predetermined display rate of 25 fps or 29.97 fps. (Very few players convert from PAL to NTSC or NTSC to PAL. See 1.19.)

It's interesting to note that even interlaced source video is often encoded as progressive-structured MPEG pictures, with interlaced field-encoded macroblocks used only when needed for motion. A computer can mostly ignore the repeat_first_field flags and re-interleave (weave) the video fields back into full-resolution progressive frames, which works especially well at 72 Hz refresh rate (3x24). Computers can improve the quality of interlaced source by doubling the lines in fields (bobbing) and displaying them as progressive frames at twice the normal rate. Most film source is encoded progressive (the inverse telecine process in the encoder removes duplicate 2-3 pulldown fields from videotape source); most video sources are encoded interlaced. These may be mixed on the same disc, such as an interlaced logo followed by a progressive movie. 

See 3.8 for an explanation of progressive and interlaced scanning. See 1.40 for progressive-scan players. See the MPEG page <> for more information on MPEG-2 video.

Picture dimensions are max 720x480 (for 525/60 NTSC display) or 720x576 (for 625/50 PAL/SECAM display). Pictures are subsampled from 4:2:2 ITU-R BT.601 down to 4:2:0, allocating an average of 12 bits/pixel in Y'CbCr format. (Color depth is 24 bits, since color samples are shared across 4 pixels.) DVD pixels are not square. The uncompressed source is 124.416 Mbps for video source (720x480x12x30 or 720x576x12x25), or either 99.533 or 119.439 Mbps for film source (720x480x12x24 or 720x576x12x24). In analog output terms, lines of horizontal resolution is usually around 500, but can go up to 540 (see 3.4.1). Typical luma frequency response maintains full amplitude to between 5.0 and 5.5 MHz. This is below the 6.75 MHz native frequency of the MPEG-2 digital signal (in other words, most players fall short of reproducing the full quality of DVD). Chroma frequency response is half that of luma.

Allowable picture resolutions are:
MPEG-2, 525/60 (NTSC): 720x480, 704x480, 352x480
MPEG-2, 625/50 (PAL): 720x576, 704x576, 352x576
MPEG-1, 525/60 (NTSC): 352x240
MPEG-1, 625/50 (PAL): 352x288

Different players use different numbers of bits for the video digital-to-analog converter. Current best-quality players use 10 bits. This has nothing to do with the MPEG decoding process, since each original component signal is limited to 8 bits per sample. More bits in the player provide more "headroom" and more signal levels during digital-to-analog conversion, which can help produce a better picture.

Maximum video bit rate is 9.8 Mbps. The "average" video bit rate is 3.5 but depends entirely on the length, quality, amount of audio, etc. This is a 36:1 reduction from uncompressed 124 Mbps video source (or a 28:1 reduction from 100 Mbps film source). Raw channel data is read off the disc at a constant 26.16 Mbps. After 8/16 demodulation it's down to 13.08 Mbps. After error correction the user data stream goes into the track buffer at a constant 11.08 Mbps. The track buffer feeds system stream data out at a variable rate of up to 10.08 Mbps. After system overhead, the maximum rate of combined elementary streams (audio + video + subpicture) is 10.08. MPEG-1 video rate is limited to 1.856 Mbps with a typical rate of 1.15 Mbps.

Still frames (encoded as MPEG-2 I-frames) are supported and can be displayed for a specific amount of time or indefinitely. These are generally used for menus. Still frames can be accompanied by audio.

A disc also can have up to 32 subpicture streams that overlay the video for subtitles, captions for the hard of hearing, captions for children, karaoke, menus, simple animation, etc. These are full-screen, run-length-encoded bitmaps with two bits per pixel, giving four color values and four transparency values. For each group of subpictures, four colors are selected from a palette of 16 (from the YCbCr gamut), and four contrast values are selected out of 16 levels from transparent to opaque. Subpicture display command sequences can be used to create effects such as scroll, move, color/highlight, and fade. The maximum subpicture data rate is 3.36 Mbps, with a maximum size per frame of 53220 bytes.

In addition to subtitles in subpicture streams, DVD also supports NTSC Closed Captions. Closed Caption text is stored in the video stream as MPEG-2 user data (in packet headers) and is regenerated by the player as a line-21 analog waveform in the video signal, which then must be decoded by a Closed Caption decoder in the television. Although the DVD-Video spec mentions NTSC only, there is no technical reason PAL/SECAM DVD players could not be made to output the Closed Caption text in World System Teletext (WST) format; the only trick is to deal with frame rate differences. Unfortunate note: DVD Closed Caption MPEG-2 storage format is slightly different than the ATSC format. See 1.45 for more about Closed Captions.

[3.4.1] What does "lines of resolution" mean?

Everyone gets confused by the term "lines of horizontal resolution," also known as LoHR or TVL. It's a carryover from analog video, it's poorly understood, it's inconsistently measured and reported by manufacturers, but we're stuck with it until all video is digital and we can just report resolution in pixels.

Technically, lines of horizontal resolution refers to visually resolvable vertical lines per picture height. In other words, it's measured by counting the number of vertical black and white lines that can be distinguished an area that is as wide as the picture is high. The idea is to make the measurement independent of the aspect ratio. Lines of horizontal resolution applies both to television displays and to signal formats such as that produced by a DVD player. Most TVs have ludicrously high numbers listed for their horizontal resolution.

Since DVD has 720 horizontal pixels (on both NTSC and PAL discs), the horizontal resolution can be calculated by dividing 720 by 1.33 (for a 4:3 aspect ratio) to get 540 lines. On a 1.78 (16:9) display, you get 405 lines. In practice, most DVD players provide about 500 lines instead of 540 because of filtering and low-quality digital-to-analog converters. VHS has about 230 (172 widescreen) lines, broadcast TV has about 330 (248 widescreen), and laserdisc has about 425 (318 widescreen).

Don't confuse lines of horizontal resolution (resolution along the x axis) with scan lines (resolution along the y axis). DVD produces 480 scan lines of active picture for NTSC and 576 for PAL. The NTSC standard has 525 total scan lines, but only 480 to 483 or so are visible. (The extra lines are black. They contain sync pulses and other information, such as the Closed Captions that are encoded into line # 21). PAL has 625 total scan lines, but only about 576 to 580 are visible. Since all video formats (VHS, LD, broadcast, etc.) have the same number of scan lines, it's the horizontal resolution that makes the big difference in picture quality.

For more information, see Allan Jayne's TV and Video Resolution Explained.

[3.5] What's widescreen? How do the aspect ratios work?

Video can be stored on a DVD in 4:3 format (standard TV shape) or 16:9 (widescreen). The width-to-height ratio of standard televisions is 4 to 3; in other words, 1.33 times wider than high. New widescreen televisions, specifically those designed for HDTV, have a ratio of 16 to 9; that is, 1.78 times wider than high.

DVD is specially designed to support widescreen displays. Widescreen 16:9 video, such as from a 16:9 video camera, can be stored on the disc in anamorphic form, meaning the picture is squeezed horizontally to fit the standard 4:3 rectangle, then unsqueezed during playback.

Things get more complicated when film is transferred to video, since most movies today have an aspect ratio of 1.66, 1.85 ("flat"), or 2.40 ("scope"). Since these don't match 1.33 or 1.78 TV shapes, two processes are employed to make various movie pegs fit TV holes:

Letterbox (often abbreviated to LBX) means the video is presented in its theatrical aspect ratio, which is wider than standard or widescreen TV. Black bars, called mattes, are used to cover the gaps at the top and bottom. A 1.85 movie that has been letterboxed for 1.33 display has thinner mattes than a 2.4 movie letterboxed to 1.33 (28% of display height vs. 44%), although the former are about the same thickness as those of a 2.4 movie letterboxed to 1.78 (26% of display height). The mattes used to letterbox a 1.85 movie for 1.78 display are so thin (2%) that they're hidden by the overscan of most widescreen TVs. Some movies, especially animated features and European films, have an aspect ratio of 1.66, which can be letterboxed for 1.33 display or sideboxed (or windowboxed) for 1.78 display.

Pan & scan means the thinner TV "window" is panned and zoomed across the wider movie picture, chopping off the sides. However, most movies today are shot soft matte, which means a full 1.33 aspect film frame is used. (The cinematographer has two sets of frame marks in her viewfinder, one for 1.33 and one for 1.85, so she can allow for both formats.) The top and bottom are masked off in the theater, but when the film is transferred to video the full 1.33 frame can be used in the pan & scan process. Pan & scan is primarily used for 1.33 formatting, not for 1.78 formatting, since widescreen fans prefer that letterboxing be used to preserve the theatrical effect.

For more details and nice visual aids see Leopold's How Film Is Transferred to Video page. A list of movie aspect ratios is at <>.