This is the 22-Jul-97 revision of the FAQ for the alt.video.dvd Usenet newsgroup. (See below for what's new.) Please send corrections, additions, and new questions to Jim Taylor firstname.lastname@example.org.
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Recent significant changes (last posted to newsgroups on July 11):
 GENERAL DVD
[1.1] What is DVD?
DVD, which stands for Digital Video Disc, Digital Versatile Disc, or nothing, depending on whom you ask, is the next generation of optical disc storage technology. It's essentially a bigger, faster CD that can hold video as well as audio and computer data. DVD aims to encompass home entertainment, computers, and business information with a single digital format, eventually replacing audio CD, videotape, laserdisc, CD-ROM, and perhaps even video game cartridges. DVD has widespread support from all major electronics companies, all major computer hardware companies, and most major movie and music studios, which is unprecedented and says much for its chances of success (or, pessimistically, the likelihood of it being forced down our throats).
It's important to understand the difference between DVD-Video and DVD-ROM. DVD-Video (often simply called DVD) holds video programs and is played in a DVD player hooked up to a TV. DVD-ROM holds computer data and is read by a DVD-ROM drive hooked up to a computer. The difference is similar to that between Audio CD and CD-ROM. DVD-ROM also includes future variations that are recordable one time (DVD-R) or many times (DVD-RAM). Most people expect DVD-ROM to be initially much more successful than DVD-Video. Most new computers with DVD-ROM drives will also be able to play DVD-Videos (see 6.1).
There's also a DVD-Audio format. The technical specifications for DVD-Audio are not yet determined.
[1.2] What are the features of DVD-Video?
Note: Most discs will not contain all features (multiple audio/subtitle tracks, seamless branching, parental control, etc.).
Most players support a standard set of features:
High-end players may include additional features:
[1.3] What's the quality of DVD-Video? Why do some demos look so bad?
DVD has the capability to produce near-studio-quality video and better-than-CD-quality audio. DVD is vastly superior to videotape, and can be better than laserdisc (see 2.7.). However, quality depends on many production factors. Until compression experience and technology improves we may often see DVDs which are inferior to laserdiscs. Also, since large amounts of video have already been encoded for VideoCD using MPEG-1, some early DVDs will use that format (which is no better than VHS) instead of higher-quality MPEG-2.
DVD video is compressed from studio ITU-R 601 format to MPEG-2 format. This is a "lossy" compression which removes redundant information (such as sections of the picture that don't change) and information that's not readily perceptible by the human eye. The resulting video, especially when it is complex or changing quickly, may sometimes contain "artifacts" such as blockiness, fuzziness, and video noise depending on the processing quality and amount of compression. At average rates of 3.5 Mbps (million bits/second), artifacts may be occasionally noticeable. Higher data rates result in higher quality, with almost no perceptible difference from the original master at rates above 6 Mbps. As MPEG compression technology improves, better quality will be achieved at lower rates.
Some DVD demos have visible artifacts such as blockiness, color banding, blurriness, missing detail, and even detail such as a face which "floats" behind the rest of the moving picture. This is sometimes caused by poor MPEG encoding, but is just as often cause by bad digital noise reduction during film-to-tape transfer or before encoding. The Free Willy and Twister excerpts on the Panasonic demo disc are good examples of this. In any case, bad demos are not an indication that DVD quality is bad, since other demos show no artifacts or other problems. Bad demos are simply an indication of how bad DVD can be if not properly processed and correctly reproduced. Early demos were shown on prototype players based on prerelease hardware and firmware. Many demo discs were rushed through the encoding process in order to be distributed as quickly as possible. Contrary to popular opinion, and as stupid as it may seem, these demos are not carefully "tweaked" to show DVD at its best. Also, most salespeople are incapable of properly adjusting a television set. Most TVs have the sharpness set too high for the clarity of DVD. This exaggerates the high-frequency video and causes distortion, just as the treble control set too high for a CD causes it to sound harsh. DVD video has exceptional color fidelity, so muddy or washed out colors are almost always a problem in the display, not in the DVD player or disc.
DVD audio quality is excellent. One of DVD's audio formats
is LPCM (linear pulse code modulation) with sampling sizes and rates higher
than audio CD. Alternately, audio for most movies is stored as discrete
multi-channel surround sound using Dolby Digital or MPEG-2 audio compression
similar to the surround sound formats used in theaters. As with video, audio
quality depends on how well the encoding was done. Most audio on DVD will
be in Dolby Digital format, which is close to CD quality.
The final assessment can't be made until DVD is in the hands of consumers. No one can yet guarantee the quality of DVD, just as no one should dismiss it based on demos or hearsay. And in the end it's a matter of individual perception.
[1.4] What are the disadvantages of DVD?
[1.5] When will DVD players and drives be available?
Some manufacturers originally announced that DVD players would be available as early as the middle of 1996. These predictions were woefully optimistic. Delivery was initially held up for "political" reasons of copy protection demanded by movie studios, but was later delayed by lack of titles.
Projected player releases (1997):
Fujitsu supposedly released the first DVD-ROM-equipped
computer on Nov. 6 in Japan. Toshiba released a DVD-ROM-equipped computer
and a DVD-ROM drive in Japan in early 1997 (moved back from December which
was moved back from November!). DVD-ROM drives from Toshiba, Pioneer, Panasonic,
Hitachi, and Sony began appearing in sample quantities as early as January
1997, but none were expected to be available before May. Creative Labs'
$499 PC-DVD upgrade kit (Matsushita drive, A/V decoder board; Warner DVD-V
sampler) went on sale in the U.S. in April for $500. Samsung drives (and
PCs with drives) were available in Korea in January. Hi-Val's $799 PC-DVD
upgrade kit (Toshiba drive, Quadrant decoder; 6 DVD-ROMS including Silent
Steel, Daedalus Encounter, and Xiphias Encyclopedia Electronica) is scheduled
for May, as is Diamond Multimedia's $599 kit STB Systems DVD Theater Upgrade
Kit will be available in July for $699. DynaTek has announced a $649 upgrade
kit with 6 titles. Philips drives will be available in the 2nd quarter.
LG Electronics drives will be available in July. Toshiba's Infinia DVD-ROM-equipped
PC will be available Spring 1997. Compaq and Sony DVD-PCs are delayed. Sony's
DVD-PCs will be out by Summer. Creative's new 2x DVD-ROM kit will be available
by Summer for $380.
Note: If you buy a player from outside your country (e.g., a Japanese player for use in the US) you may not be able to play region-locked discs on it. (See 1.10.)
[1.6] When will DVD titles be available, and how many?
As with hardware, rosy predictions of hundreds of movie titles for Christmas of 1996 failed to materialize. But, as they say, "time weals all hounds." But enough of welts on dogs. Let's get back to DVD. Only a handful of DVD titles, mostly music videos, were available in Japan for the November 1996 launch of DVD. Actual feature films began to appear in December. Movies appeared in the US in March of 1997. Currently (April 4) there are over 30 titles available and over 150 that have been announced. Compared to other launches (CD, LD, etc.) this is a huge number. Almost 19,000 discs were purchased in the first two weeks of the US launch -- more than expected. Info-Tech predicts over 600 titles by the end of 1997 and more than 8,000 titles by 2000.
For a complete list of titles available in the US and Canada, see http://www.unik.no/~robert/hifi/dvd/film1.html, and for titles in Japan and Europe see http://www.unik.no/~robert/hifi/dvd/film2.html. New release lists and announcements are also available at http://www.laserviews.com.
Concorde Video is releasing 12 Monkeys in Germany at the end of March. This is a special edition, dubbed in German, limited to 5000 copies, priced at DM49,95. Call +49-711-182-1229 or email email@example.com.
DVD-ROM software will slowly appear. Approximately 50% of CD-ROM producers have announced intentions to develop for DVD-ROM. As of Aug. 1996, 30 DVD-ROM titles are supposedly in development for early 1997 release. IDC expects over 13 percent of all software will be available in DVD-ROM format by the end of 1998. In one sense, DVD-ROMs are simply larger faster CD-ROMs and will contain the same material. But DVD-ROMs can also take advantage of the MPEG video and multi-channel audio capabilities being added to many DVD-ROM-equipped computers.
The first DVD-ROMs will probably be "The Union Catalogue of Belgian Research Libraries" from IVS, "PhoneDisc PowerFinder USA One" (which filled 6 CD-ROMs) from Digital Directory Assistance Inc., and "Silent Steel" from Tsunami Media.
[1.7] How much do players and drives cost?
Mass-market DVD movie players currently list for $600 and up. (See 1.5 for models and prices.) Within a few years they may approach VCR prices. InfoTech predicts prices will be as low as $250 by the year 2000.
DVD-ROM drives for computers sell for around $400 to $500. (OEM prices are under $350.) Prices are expected to drop quickly to current CD-ROM drive levels.
[1.8] How much do discs cost?
It will vary. Many studios have promised that DVDs will be as cheap or cheaper than videotapes (and much cheaper than laserdiscs). This remains to be seen, especially for special editions with supplemental material which cost much more to produce. Some new releases will initially be priced for rental (near $80, the same as VHS). But existing titles, which have already made back money, are expected to be priced below $25 on DVD. Time Warner has set a price of $24.98 in the U.S. (3,000 yen in Japan). Polygram's sell-trhough discs are $29.99. Columbia TriStar says its feature film DVDs will be somewhere between VHS and laserdisc prices.
DVD-ROMs will initially be slightly more expensive than CD-ROMs since there is more stored on them, they cost more to replicate, and the market is smaller. But as costs drop and the installed base of drives grow, DVD-ROMs will probably cost the same as CD-ROMs do today.
[1.9] How quickly will DVD become established?
Nobody knows. Here are a few predictions:
For comparison, there are about 600 million audio CD players and 100 million CD-ROM drives worldwide. There are about 80 million VCRs in the U.S. and about 250 million worldwide.
[1.10] What are "regional codes," "country codes," or "zone locks"?
Motion picture studios want to control the home release of movies in different countries because theater releases aren't simultaneous (a movie may come out on video in the U.S. when it's just hitting screens in Europe). Therefore they have required that the DVD standard include codes which can be used to prevent playback of certain discs in certain geographical regions. Players sold in each region will include a built-in code. The player will refuse to play discs which are not allowed in the region. This means that discs bought in one country may not play on players bought in another country.
Regional codes are entirely optional. Discs without codes will play on any player in any country. It's not an encryption system, it's just one byte of information on the disc that the player checks. Some studios have already announced that only their new releases will have regional codes. Presumably, once a DVD movie has achieved worldwide release it could be re-released without coding.
There are 6 regions (also called "locales"). Players and discs are identified by the region number superimposed on a world globe. If a disc plays in more than one region it will have more than one number on the globe.
(See the map at http://www.unik.no/~robert/hifi/dvd/world.html.)
Some players have been modified to play discs regardless of their regional codes. Sources include <http://www.gamestop.com/avex>. Buy at your own risk. The warranty is probably void on modified players.
Regional codes also apply to DVD-ROM systems, but are officially recommended for use only with DVD-Video discs, not DVD-ROM discs containing computer software. Operating systems including upcoming versions of Windows and MacOS will check for regional codes before playing movies from a DVD-Video. It's likely that regional codes will apply to DVD-Audio.
[1.11] What are the copy protection issues?
There are three forms of copy protection used by DVD:
1) Videotape (analog) copying is prevented with a Macrovision 7.0 or similar circuit in every player. The general term is APS (Analog Protection System). Computer video cards with composite or s-video (Y/C) output must also use APS. Macrovision adds a rapidly modulated colorburst signal ("Colorstripe") along with pulses in the vertical blanking signal ("AGC") to the composite video and s-video outputs. This confuses the synchronization and automatic-recording-level circuitry in 95% of consumer VCRs. Unfortunately, it can degrade the picture, especially with old or nonstandard equipment. Macrovision may show up as stripes of color, distortion, rolling, black & white picture, and dark cycling. Macrovision creates severe problems for most line doublers. Macrovision is not present on analog component video output of early players, but is required for newer players such as the Sony S700 (AGC only, since there is no colorburst in a component signal). The discs themselves tell the player whether or not to enable Macrovision AGC with or without Colorstripe. The producer of the disc decides what amount of copy protection to enable and then pays Macrovision royalties accordingly. Just as with videotapes, some DVDs are Macrovision-protected and some aren't. (For Macrovision details see SGS/Thomson's video encoder datasheet at http://www.st.com/stonline/books/ascii/docs/4570.htm.)
2) Each disc also contains information specifying if the contents can be copied. This is a "serial" copy generation management system (CGMS) designed to prevent copies, or to prevent copies of copies. The CGMS information is embedded in the outgoing video signal. For CGMS to work, the equipment making the copy must recognize and respect the CGMS. The analog standard (CGMS/A) encodes the data on NTSC line 21. The digital standard (CGMS/D) is not yet finalized, but will apply to digital connections such as IEEE 1394/Firewire.
3) Because of the potential for perfect digital copies, paranoid movie studios forced a deeper copy protection requirement into the DVD-Video standard. Content Scrambling System (CSS) is a form of data encryption to discourage reading media files directly from the disc. Most players have a decryption circuit that decodes the data before displaying it. No unscrambled digital output is allowed until work in progress for secure digital connections is finished. On the computer side, DVD-ROM drives and video display/decoder hardware or software exchange encryption keys so that the video is decrypted just before being displayed by the encoder. This means that many DVD-ROM drives and video display boards have extra hardware (and cost) for movie copy protection. In 1999, all DVD-ROM drives will be required to support regional management in conjunction with CSS. The region code can optionally be be reset a limited number of times by the user. Makers of equipment used to display DVD-Video (drives, chips, display boards, etc.) must license CSS. There is no charge for a CSS license, but it's currently a lengthy process, so it's recommended that interested parties apply as soon as possible. Near the end of May 1997, CSS licenses were finally granted for software decoding.
Movie studios and consumer electronics companies want to make it illegal to defeat DVD copy protection, and are pursuing legislation in the U.S. and other countries. A co-chair of the legal group of the copy protection committee stated, "in the video context, the contemplated legislation should also provide some specific assurances that certain reasonable and customary home recording practices will be permitted, in addition to providing penalties for circumvention." It's not at all clear how this might be "permitted" by a player.
CSS is allowed for DVD-video content only. Of course, since a DVD-ROM can hold any form of computer data, any desired encryption scheme can be implemented.
All three forms of copy protection are optional for the producer of a disc. Movie decryption is also optional for hardware and software playback manufacturers: a player or computer without decryption capability will only be able to play unencrypted movies.
These copy protection schemes are designed only to guard against casual copying (which the studios claim causes billions of dollars in lost revenue). The goal is to "keep the honest people honest." Even the people who developed the copy protection standards admit that it won't stop well-equipped pirates. There are inexpensive devices that defeat analog copy protection, but Macrovision claims none of the devices are effective against the new Colorstripe feature (yet).
[1.12] What about DVD-Audio or Music DVD?
The DVD Consortium has decided to seek additional input from the music industry before defining the DVD-Audio format. An audio standard probably won't appear until the end of 1997 at the earliest. If the final specification includes features or formats not present in the current DVD specification, existing DVD players may not be able to play new DVD-Audio discs.
Sony is pushing for its Direct Stream Digital (DSD) format, with the support of Philips. Other organizations such as Acoustic Renaissance for Audio (ARA) prefer lossless compressed PCM that's more appropriate for studio work and archiving.
There are rumors that the DVD Consortium is pushing for an 8 cm (CD-single) size, while the audio industry wants a 12 cm size. (The existing DVD physical spec allows both sizes.) The audio industry also wants "legacy" discs which will play on one side in existing CD players and on the other side in DVD players. There are technical difficulties in doing this, but it may be possible.
The music industry is also requesting an "embedding signalling" or "digital watermark" copy protection feature. This applies a digital signature to the audio in the form of supposedly inaudible "noise" so that new equipment will recognize copied audio and refuse to play it. Audiophiles claim this degrades the audio.
In the meantime, the DVD-Video standard includes surround sound audio and better-than-CD audio (see 3.6). Pioneer is developing audio-only players based on the audio portion of DVD-Video.
[1.13] Which studios are supporting DVD? Didn't some studios say they won't support it?
Warner, Columbia TriStar, MGM, Polygram, and others are releasing movies on DVD (see 1.6). Others have announced support but no movies yet (see 6.2 for a full list). Disney has expressed concerns over copying, but is closely involved in DVD development and will most likely jump in once copy protection is resolved (see 1.11). Paramount and 20th Century Fox have no immediate plans for DVD. Other studios may hold back, but if DVD is a success no studio would be foolish enough to not jump on the bandwagon.
[1.14] Will DVD record from VCR/TV/etc?
Short Answer: No. (Not in this century.)
Long answer: The minimum requirement for reproducing audio and video on DVD is an MPEG video stream and a PCM audio track. (Other streams such as Dolby Digital audio, MPEG audio, and subpicture are not necessary for the simplest case.) Basic DVD control codes are also needed. At the moment it's difficult in real time to encode the video and audio, combine them with the control codes, and write the whole thing to DVD. Even if you could do all this in a home recorder, it would be extremely expensive. Prices for DVD production systems are dropping from millions of dollars to thousands of dollars, but they won't be in the <$500 range for home use for several years yet. In June 1997, Hitachi demonstrated a home DVD video recorder containing a DVD-RAM drive, a hard disk drive (as a buffer), two MPEG-1 encoders, and an MPEG-2 decoder. No production date was mentioned. It's possible the first home DVD recorders will require a digital source of already-compressed audio and video, such as DBS.
Other obstacles: Price of blank discs may initially be as high as $50 for record-once, and even higher for erasable. The first generation of recordable media will hold only about 3/4 as much as pre-recorded discs. Realtime compression will require higher bit rates for decent quality, lowering capacity even more. MPEG-2 compression works much better with high-quality source, so recording from VHS or broadcast/cable may not give very good results (unless the DVD recorder has prefilters, which raises the cost).
Don't be confused by DVD-R and DVD-RAM systems, which will be available soon and will cost over $10,000 (see 4.3). These can record data, but to create full-featured DVD-Videos would require additional hardware and software to do video encoding (MPEG-2), audio encoding (Dolby Digital or MPEG or LPCM), subpicture encoding (run-length-compressed bitmaps), still frame encoding (MPEG-1 or MPEG-2), control code generation, and multiplexing. And since this can't be done in real time, you'd also need a 5 to 9 GB hard drive to premaster the data to.
Some people believe that recordable DVD-Video will never be practical for consumers to record TV shows or home videos, since digital tape is more cost effective. On the other hand, digital tape lacks many of the advantages of DVD such as seamless branching, instant rewind/fast forward, instant search, and durability, not to mention the coolness of small shiny discs. So once the encoding technology is fast and cheap enough, and the blank discs are cheap enough, recordable DVD may be a reality. It will be an interesting contest between DVD and digital video tape (DV). DV is out already, but decks cost $4,000.
[1.15] What happens if I scratch the disc? Aren't discs too fragile to be rented?
Most scratches will cause minor channel data errors that are easily corrected. A common misperception is that a scratch will be worse on a DVD than on a CD because of higher storage density and because video is heavily compressed. DVD data density (say that fast ten times!) is physically four times that of CD-ROM, so it's true that a scratch will affect more data. But DVD error correction is at least ten times better and more than makes up for the density increase. It's also important to realize that MPEG-2 and Dolby Digital compression are partly based on removal or reduction of imperceptible information, so decompression doesn't expand the data as much as might be assumed. Major scratches may cause uncorrectable errors that will cause an I/O error on a computer or show up as a momentary glitch in DVD-Video picture. However, there are many schemes for concealing errors in MPEG video (see section D.12 of http://icib.igd.fhg.de/icib/it/iso/cd_13818-2/read1.html.
The DVD computer advisory group specifically requested no mandatory caddies or other protective carriers. Consider that laserdiscs, music CDs, and CD-ROMs are likewise subject to scratches, but many video stores and libraries rent them. West Coast Entertainment will be renting (and selling) DVDs and renting players beginning on March 25th in 57 stores in the New Jersey and New York markets. Sony and Blockbuster are placing DVD demo kiosks in select Blockbuster stores. Sony's DVD player includes coupons for free DVD rentals at Blockbuster.
[1.16] VHS is good enough, why should I care about DVD?
The primary advantages of DVD are quality and extra features (see 1.2). DVD will not degrade with age or after many playings like videotape will (which is an advantage for parents with kids who watch Disney videos twice a week!). This is the "collectability" factor present with CDs vs. cassette tapes.
If none of this matters to you, then VHS probably is good enough.
[1.17] Is the packaging different from CD?
Manufacturers are worried about customers assuming DVDs will play in their CD player, so they would like the packaging to be different. Time Warner is promoting a "Snapper" package (similar in form to the plastic and paper "eco" CD packages) which measures 14cm wide x 19cm high x 1.25cm thick (5.5" x 7.5" x 0.5"). [I measured it by hand, so this may not be exact.] This is about as wide as a CD jewel box and about as tall as a VHS cassette box. There is also a proposal from the Video Software Dealers Association for a package 5 5/8" wide, 7 3/8" high and between 3/8" and 5/8" deep. However, no one is being forced to use a larger package size and many companies will undoubtedly use standard jewel cases. It remains to be seen if any package becomes standard, especially for DVD-ROM.
[1.18] What's a dual-layer disc? Will it work in all players?
A dual-layer disc has two layers of data, one of them semi-transparent. Since both layers are readable from the same side, a dual-layer disc can hold almost twice as much as a single-layer disc, for over 4 hours of video (see 3.3 for more details). A few dual-layer discs are currently available (such as GoldenEye, Species, Raging Bull and Rain Man). Initially only a few replication plants could make dual-layer discs, but most plants now have the capability. The second layer can either have a "PTP" track that runs in parallel to the first track (for independent data or special switching effects), or an "OTP" track that runs opposite to the first track that is the pickup head reads out from the center on the first track, then in from the outside on the second track. This is designed to provide continuous video across both layers. There's no guarantee that the switch between layers will be seamless, but non-seamless switches usually take less than a second. The "seamlessness" depends as much on the way the disc is laid out as on the design of the player. This is a feature of DVD that still has rough edges to work out.
All DVD players and drives can play dual-layer discs -- it's required by the spec. All players and drives also play double-sided discs if you flip them over. No manufacturer has announced a model that will play both sides. The added cost is probably not justifiable since discs can use two layers instead of two sides. Pioneer LD/DVD players can play both sides of an LD, but not a DVD. (See 2.9 for note on reading both sides simultaneously.)
There are various ways to recognize dual-layer discs: 1) the gold color, 2) a menu on the disc for selecting the widescreen or letterbox version, 3) two serial numbers on one side.
[1.19] Is DVD-Video a worldwide standard? Does it work with NTSC, PAL, and SECAM?
DVD-V has the same NTSC vs. PAL problem as videotape and laserdisc. DVD-V supports two mutually-incompatible television systems: 525/60 (NTSC) and 625/50 (PAL). There are three differences between discs intended for playback on different systems: picture size (720x480 vs. 720x576), display frame rate (29.97 vs 25), and surround audio (Dolby Digital vs. MPEG-2). (See 3.4 and 3.6 for details.) Movies are stored at 24 frames/sec but are encoded for one of the two display rates.
However, a producer can choose to include additional video and audio --at the expense of playing time-- so that all formats are covered. It's unknown if players will be able to automatically recognize and play the correct video track. Some studios include Dolby Digital tracks along with the MPEG audio tracks on their PAL discs.
Some players will only play NTSC discs, some players will only play PAL discs, and some will play both. Multi-standard players will output NTSC from a 525/60 disc and PAL from a 625/50 disc. This requires two TVs or a multi-standard TV that can display both. Some players partially convert NTSC to 60 Hz PAL, which requires a 60 Hz PAL TV. It's also possible to make a standards-converting player that will output standard NTSC from a 625/50 disc or standard PAL from a 525/60 disc, but so far no such players have been announced.
There are actually three types of DVD players if you count computers. Most DVD playback software and hardware can play both NTSC and PAL from a DVD-Video.
[1.20] What about animation on DVD? Doesn't it compress poorly?
Some people claim that animation, especially hand-drawn cell animation such as cartoons and anime, does not compress well with MPEG-2 or even ends up larger than the original. Other people claim that animation is simple so it compresses better. Neither is true.
Supposedly the "jitter" between frames caused by differences in the drawings or in their alignment causes problems. An animation expert at Disney pointed out that this doesn't happen with modern animation techniques. And even if it did, the motion estimation feature of MPEG-2 would compensate for it.
Because of the way MPEG-2 breaks a picture into blocks and transforms them into frequency information it can have a problem with the sharp edges common in animation. This loss of high-frequency information can show up as "ringing" or blurry spots along edges (called the Gibbs effect). However, at the data rates commonly used for DVD this problem does not occur.
[1.21] Why do some discs require side flipping? Can't DVDs hold four hours per side?
Even though DVD's dual-layer technology (see 3.3) allows over four hours of continuous playback, some movies are split over two sides of a disc, requiring that it be flipped partway through (no players can automatically flip the disc yet). This is usually because the producers were too lazy to optimize the compression or to make a dual-layer disc. Better picture qual;ity is a lame excuse for increasing the data rate; in many cases the video will look better if carefully encoded at a lower bit rate. Lack of dual-layer production capability is also a lame excuse; at first very few DVD plants could make dual-layer discs but this is no longer the case. Unless a movie is more than 4 hours long, it can easily fit on one dual-layer disc. The following movies require flipping. (Note: This is note the same as a disc with a widescreen version on ne side and a pan & scan version on the other.)
[1.22] Why is the picture squished, making things look too skinny?
Answer: RTFM. You are watching an anamorphic picture intended for display only on a widescreen TV. (See 3.5 for technical details). You need to go into the player's setup menu and tell it you have a standard 4:3 TV, not a widescreen 16:9 TV. It will then automatically letterbox the picture so you can see the full width at the proper proportions. In some cases you can change the aspect ratio as the disc is playing (by pressing the "aspect" button on the remote control. On Pioneer players, you have to stop the disc before you can change aspect.
[1.23] Do all videos use Dolby Digital (AC-3)? Do they all have 5.1 channels?
Most DVD-Video discs contain Dolby Digital soundtracks. However, it's not required. Some discs, especially those containing only audio, have PCM tracks. It's also possible for a disc to contain only MPEG audio, but MPEG is mostly being ignored, and is included on PAL discs for technical conformance only.
Do not assume that the "Dolby Digital" label is a guarantee of 5.1 channels. A Dolby Digital soundtrack can be mono, dual mono, stereo, Dolby Surround stereo, etc. Some DVD packaging has small lettering under the Dolby Digital logo that indicates if there are 5.1 channels. In some cases, there is more than one Dolby Digital track: a 5.1-channel track and a track specially remixed for stereo Dolby Surround.
See 3.6 for more audio details.
[1.24] Can DVDs have laser rot?
Laserdiscs are subject to what's commonly called laser rot: the deterioration of the aluminum layer that can occur if the seal between disc sides is broken. The large size of laserdiscs makes them flexible, thus allowing more movement along the bond between sides. DVDs are much more rigid. Also, DVDs are molded from polycarbonate, which absorbs about ten times less moisture than the PMMA used for laserdiscs. It's too early to know for sure, but DVD's will probably have few or no laser rot problems.
[1.25] Which titles are pan & scan only? Why?
Some titles are available only in pan & scan because there was no letterbox or anamorphic transfer made from film. (See 3.5 for more info on pan & scan.) Since transfers cost $50,000 to $100,000, studios may not think a new transfer is justified. In some cases the original film or rights are no longer available for a new transfer. In the case of old movies, they were shot full frame so there is no widescreen version. The following DVD titles are pan & scan or full frame. A detailed list is also available at http://www.unik.no/~robert/hifi/dvd/film1.html.
 DVD's relationship to other products
[2.1] Will DVD replace VCRs?
Not any time soon. DVD is not yet recordable (see 1.14) and 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:
[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 stated that their DVD hardware will 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.)
[2.4.2] Is CD-ROM compatible with DVD-ROM?
Yes. All DVD-ROM drives will read CD-ROMs (Yellow Book). However, DVD-ROMs are not readable by CD-ROM drives.
[2.4.3] Is CD-R compatible with DVD-ROM?
Maybe. 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. This problem is being addressed in many ways. Sony has developed a twin-laser pickup in which one laser is used for reading DVDs and the other for reading CDs and CD-Rs. Samsung has also announced dual-laser using a holographic annular masked lens. These solutions provide complete backwards compatibility with millions of CD-R discs. Philips has also stated that its DVD-ROM drives will read CD-Rs. In addition, new CD-R Type II blanks that will work with CD-ROM and DVD are supposedly in development. In the meantime, some first-generation DVD-ROM drives and many first-generation DVD-Video players will not read CD-R media.
[2.4.4] Is CD-RW compatible with DVD?
Supposedly. CD-Rewritable (Orange Book Part III) discs can not be read by existing CD-ROM drives and CD players. CD-RW has a lower reflectivity difference, requiring automatic-gain-control (AGC) circuitry. The new "MultiRead" standard addresses this and some DVD manufacturers have already suggested they will support it. Supposedly the optical circuitry of DVD-ROM drives and DVD players is good enough to read CD-RW. CD-RW does not have the "invisibility" problem of CD-R (see 2.4.3).
[2.4.5] Is VideoCD compatible with DVD?
Sometimes. It's not required by the DVD spec, but it's trivial to support the White Book standard since any MPEG-2 decoder can also decode MPEG-1 from a Video CD. Panasonic, RCA, Samsung, and Sony models play Video CDs. Japanese Pioneer models play Video CDs but American models don't. Toshiba players 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 the entire 48 lines (17%) off the bottom and none off the top. The Sony looks better. [Does anyone know if it cuts 24 lines off the top and the bottom, or if it scales the full picture to fit?]
Most DVD-ROM computers will be able to play Video CDs (with the right software), since its already possible with current-model CD-ROM computers.
Note: Many Asian VCDs achieve "two" soundtracks by putting one language on the left channel and another on the right. They will be mixed together into babel on a stereo system unless you adjust the balance to get only one channel.
[2.4.6] Is Photo CD compatible with DVD?
Not yet. Since Photo CDs are usually on CD-R media, they may 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.
[2.4.7] Is CD-i compatible with DVD?
In general, no. Most DVD players will not play CD-i (Green Book) discs. However, Philips has announced that it will make a DVD player that supports CD-i. Some people expect Philips to create a "DVD-i" format in attempt to breathe a little more life into CD-i (and recover a bit more of the billion or so dollars they've invested in it).
[2.4.8] 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 may be a problem with DVD-ROM drivers skipping track zero (as has been the case with some new CD-ROM drivers).
[2.4.9] 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.
[2.4.10] Is CDV compatible with DVD?
Sort of. CDV, sometimes called Video Single, is actually a weird combination of CD and laserdisc. Part 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 system. However, Pioneer and others have announced combination players that will play DVDs, laserdiscs, and CDVs.
[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 and Samsung have announced combo players that will play laserdiscs and DVDs (and also CDVs and audio CDs). Denon is rumored to have an LD/DVD player in the works also.
[2.6] Will DVD replace laserdisc? Should I buy laserdisc now or wait for DVD and HDTV?
DVD will probably replace laserdisc, but not for a very long time. Laserdisc is well established as a videophile format. There are over 9,000 laserdisc titles in the US and a total of over 35,000 worldwide that can be played on over 7 million laserdisc players. It will take DVD many years to reach this point. Until then laserdisc has the superiority of tenure. Pioneer and other laserdisc companies have committed to supporting it for years to come. There's no reason to stop buying laserdiscs, especially rare titles that may not appear on DVD for a long while if ever. Even laserdisc owners who buy DVD will not immediately replace their collection. Laserdisc and DVD will co-exist for a long while.
In December of 1996 the FCC approved the U.S. DTV standard. HDTVs may appear as early as 1998 but they will be very expensive and won't become widespread for many years. DVD will look better on HDTVs but it won't provide high resolutions (see 2.9).
The answer to this question depends on you. If you need to be the first on your block with the latest gadget, you may want to get a DVD player or a combination LD/DVD player now. If you prefer to wait until DVD prices drop and bugs get worked out, you may have a lengthy wait. If you think DVD isn't a big enough improvement and decide to hold out for HTDV, you'll be in for an even longer wait. In the meantime you could be enjoying the large selection of laserdisc titles. Or you could start saving now for DVD (which won't be too expensive) or HDTV (which will be). If you buy a laserdisc player, a surround sound system, and speakers, they will be still be useful even after DVD and HDTV come out. HDTV will require a new TV set, but it will be compatible with the rest of your gear.
Unfortunately, anticipation of DVD is already hurting laserdisc. In 1996 laserdisc player sales were down 37% even though sales of VCRs and hi-fi/surround systems were up. But silver lining in this cloud is that disc prices may come down. (Laserdisc movie sales were only down 2.5% in 1996.)
[2.7] How does DVD compare to laserdisc?
This is a dangerous question to answer, given the legions of laserdisc fanatics who would rather have their laserdiscs pried from their cold dead fingers than switch! But I'm a bit fanatical myself: I've used laserdiscs since 1979 and I work for a company whose major product is laserdiscs; so I'll give it a shot. <Putting on flameproof suit....>
Again, it will take years for DVD to reach the number of titles, installed base, and even quality of production that laserdisc has. DVD and laserdisc will coexist for at least another decade. But the potential of DVD can't be ignored -- it's the most likely long-term successor to laserdisc.
For more laserdisc info, see the Laserdisc FAQ at http://www.cs.tut.fi/~leopold/Ld/FAQ/index.html. This document is also available online here at the Laser Rot site at http://www.laserrot.com/info/info-main.html.
[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] Will DVD support HDTV (DTV/ATV)?
HDTV is not directly supported by DVD-Video. HDTV standards were not 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 video formats. DVD does use the 16:9 aspect ratio of HDTV. Since most HDTV systems are based on MPEG-2, it could be easy to "upgrade" the DVD format. The limited data rate of DVD may make it difficult to support high-quality HDTV, but this can be solved by increasing the spin rate (a double-speed DVD-ROM drive exceeds the 19 Mbps US DTV data rate) or by using higher-capacity blue or purple lasers (already demonstrated by Toshiba and others). Either case will require new players and additional standards. It's expected that future DVD players will convert video from existing discs to the standard-resolution progressive scan DTV formats (704x480x24P and 704x480x30P).
The resolution and frame rates of DTV in the US will probably correspond to the ATSC recommendations: 704x480 (24P, 30P, 60I, 60P), 1280x720 (60P), 1920x1080 (30P). The first set is "standard definition" and matches DVD. The second two are "high definition" at 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. In other words, DVD does not currently support the higher levels of HDTV systems. However, HDTVs will include connectors that work with DVD players. Existing DVD players and discs will work perfectly with HDTV sets, and will look better than any other existing consumer video format.
At some point, HDTV displays will support component digital video connections (YCrCb) or digital data connections (FireWire/IEEE 1394) along with standard component and composite analog video connections. 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 able to ouput any kind of data (even formats newer than the player) to any sort of external display or converter.
HDTV sets will appear in 1998 at very high prices. It will take many years before even a small percentage of households have HDTVs. Those who postpone purchasing a DVD player because of HDTV are in for a long wait. At some point there will be an "HDVD" format, probably around 2003 at the earliest. HDVD players will play current DVD discs, and will make them look even better on HDTV displays. Ironically, DVD-ROM computers will support HDTV before DVD-Video players, since 2x drives coupled with appropriate playback and display hardware can already meet the requirements of HDTV.
Some have speculated that a "double-headed" player reading both sides of the disc at the same time could double the data rate 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. Keeping both sides in sync would require independently tracking heads, precise track and pit spacing, and a larger, more sophisticated track buffer.
 DVD TECHNICAL DETAILS
[3.1] What are the outputs of a DVD player?
Most DVD players will have the following output connections:
Most of the DVD players with component outputs use YUV, which is incompatible with RGB. European players with SCART connectors have RGB outputs. YUV to RGB transcoders are rumored to be available for $200-$300, but seem hard to track down.
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 uses the term YUV in its generic sense to refer to color difference signals.
No DVD players have yet been announced with digital video outputs, but it's expected that at some point digital output will be available using FireWire (IEEE 1394) connectors (see http://firewire.org).
[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 option with the best quality (indicated below) that is supported by your video and audio systems.
Note: 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. This usually shows up as a repeated darkening and lightening of the picture.
Note: Most DVD players support widescreen signalling, 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.
Note: All DVD players have either a built-in Dolby Digital (AC-3) or MPEG-1 audio decoder, or both. MPEG-2 audio decoders are not currently available. The decoder translates multi-channel audio into PCM audio. This is fed to the digital output and also converted to analog for standard audio output.
[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. 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 holds around 135 minutes. A two-hour movie with three soundtracks can average 5.2 Mbps. A dual-layer disc can hold a two-hour movie at an average of 9.5 Mbps (very close to the 10.08 Mbps limit).
Capacities of DVD:
For reference, a CD-ROM holds about 650 MB (megabytes),
which is 0.64 GB (gigabytes) or 0.68 G bytes (billion bytes). In the list
below, SS/DS means single-/double-sided, SL/DL means single-/dual-layer,
GB means gigabytes (2^30), G means billions of bytes (10^9).
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 http://www.mpeg.org/MPEG/DVD/General/Gain.html.
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 .4 um to .44 um. In addition, the reference scanning velocity is slightly faster -- 3.84 m/s, as opposed to 3.49 m/s for single layer discs. Bigger pits, spaced farther apart, are easier to read correctly and are less susceptible to jitter. Bigger pits and fewer of them mean reduced capacity per layer.
See 4.3 for details of recordable DVD (DVD-R and DVD-RAM).
[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 systems are 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. 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 3-2 pulldown for 60 (59.94) Hz displays or 2-2 pulldown (with 4% speedup) for 50 Hz 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 arrive at the predetermined display rate of 25 fps or 29.97 fps. (No current players convert from PAL to NTSC or NTSC to PAL. See 1.19.) It's interesting to note that even interlaced source video is usually encoded as progressive-structure MPEG pictures, with interlaced field-encoded macroblocks used only when needed for motion. On a computer, which is not tied to the diaplay refesh rate, the repeat_first_field flags are mostly ignored and the video is shown as progressive frames at the original rate. Computers can also improve the quality of interlaced source by doubling fields and displaying them as progressive frames at twice the normal rate. See the MPEG page http://www.mpeg.org for more information on MPEG-2 video.
Picture dimensions are max 720x480 (29.97 frames/sec) or 720x576 (25 frames/sec). Pictures are subsampled from 4:2:2 ITU-R 601 down to 4:2:0, allocating an average of 12 bits/pixel. (Color depth is still 24 bits, since color samples are shared across 4 pixels.) 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). Using the traditional (and rather subjective) television measurement of "lines of horizontal resolution" DVD can have 540 lines on a standard TV (720/(4/3)) and 405 on a widescreen TV (720/(16/9)). In practice, most DVD players provide about 500 lines because of filtering. VHS has about 230 (172 w/s) lines and laserdisc has about 425 (318 w/s).
Different players use different numbers of bits for the video digital-to-analog converter. (Sony and Toshiba use 10 bits, Pioneer and Panasonic use 9 bits.) This has nothing to do with the MPEG decoding process. It provides more "headroom" and more analog signal levels which supposedly gives a better picture.
Maximum video bitrate is 9.8 Mbps. The "average" bitrate is 3.5 but depends entirely on the length, quality, amount of audio, etc. This is a 36:1 reduction from uncompressed 124 Mbps (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-2I-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, karaoke, menus, simple animation, etc. These are full-screen, run-length-encoded bitmaps limited to four pixel types. For each group of subpictures, four colors are selected from a palette of 16 (from the YCrCb 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.
[3.5] 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 16:9 format is "anamorphic,"
meaning the picture is squeezed horizontally to fit a 4:3 rectangle then
unsqueezed during playback. DVD players output widescreen video in four
Video stored in 4:3 format is not changed by the player. It will appear normally on a standard 4:3 display. Widescreen systems will either enlarge it or add black bars to the sides. 4:3 video may be formatted in various ways before being transferred to DVD. For example, it may have been letterboxed to hold video with a wider shape. Or it may have been panned & scanned from film composed for a wider theatrical presentation. All formatting done to the video prior to it being stored on the disc is transparent to the player. It merely reproduces the signal in standard format.
For automatic letterbox mode, the player uses a "letterbox filter" that creates black bars at the top and the bottom of the picture (60 lines each for NTSC, 72 for PAL). This leaves 3/4 of the height remaining, creating a shorter but wider rectangle. In order to fit this shorter rectangle, the picture is squeezed vertically by combining every 4 lines into 3. This compensates for the original horizontal squeezing, resulting in the movie being shown in its full width. The vertical resolution is reduced from 480 lines to 360.
For automatic pan & scan mode, the video is unsqueezed to 16:9 and a portion of the image is shown at full height on a 4:3 screen by following "center of interest" coordinates that are encoded in the video stream according to the preferences of the people who transferred the film to video. The pan & scan "window" is 75% of the full width, which reduces the horizontal pixels from 720 to 540. The pan & scan window can only travel laterally. This does not duplicate a true pan & scan process in which the window can also travel up and down and zoom in and out. Therefore, most DVD producers are putting a separate pan & scan version on the disc in addition to the widescreen version.
For widescreen mode, the video is stretched back out by widescreen equipment to its original width. If anamorphic video is shown on a standard 4:3 display, people will look like they have been on a crash diet. Widescreen mode is complicated because most movies today are shot with a "soft matte." (The cinematographer has two sets of frame marks in her viewfinder, one for 1.33 (4:3) and one for 1.85, so she can allow for both formats). A few movies are even wider, such as the 2.35 ratio of Panavision. Since most movies are wider than 1.78 (16:9), one of at least 4 methods must be used during transfer to make it fit the 1.78 rectangle: 1) add additional thin black bars to the top and bottom; 2) include a small amount of extra picture at the top and bottom from the soft matte area; 3) crop the sides; 4) pan & scan with a 1.78 window. With the first two methods, the difference between 1.85 and 1.78 is so small that the letterbox bars or extra picture are hidden in the overscan area of most televisions. Nevertheless, and especially with 2.35 movies, some DVD producers put 16:9 source on one side (or layer) of the disc and 4:3 source on the other. This way the full-frame version of the film can be used for a horizontal and vertical pan & scan & zoom process with no letterbox bars and no reduction in resolution.
Anamorphosis causes no problems with line doublers, which simply double the lines before they are stretched out by the widescreen display.
For anamorphic video, the pixels are fatter. Different pixel aspect ratios (none of them square) are used for each aspect ratio and resolution. 720-pixel and 704-pixel sizes have the same aspect ratio because the first includes overscan. Note that "conventional" values of 1.0950 and 0.9157 are for height/width (and are tweaked to match scanning rates). The table below uses less-confusing width/height values (y/x * h/w).
Playback of widescreen material can be restricted. Programs can be marked for the following display modes:
[3.6] What are the audio details?
The DVD-Audio format is not yet specified. The International Steering Committee announced it expects to have a final draft specification by December 1997. This means DVD-Audio products may show up around 1999.
The following details are for audio tracks on DVD-Video.
Some DVD manufacturers such as Pioneer are developing audio-only players
using the DVD-Video format.
Two additional optional formats are supported: DTS and SDDS. Both require external decoders.
The ".1" refers to a low-frequency effects (LFE) channel that connects to a subwoofer. This channel carries an emphasized bass audio signal.
All five audio formats support karaoke mode, which has two channels for stereo (L and R) plus an optional melody channel (M) and two optional vocal channels (V1 and V2).
Discs containing 525/60 (NTSC) video must use PCM or Dolby Digital on at least one track. Discs containing 625/50 (PAL/SECAM) video must use PCM or MPEG audio on at least one track. Additional tracks may be in any format. The DVD Forum has clarified that only stereo MPEG audio is mandatory for 625/50 discs, while multichannel MPEG-2 audio is recommended. Since multichannel MPEG-2 decoders are not yet available, most 625/50 discs include Dolby Digital audio.
For stereo output (analog or digital), all NTSC players and all PAL players (so far) have a built-in Dolby Digital decoder which downmixes from 5.1 channels (if present on the disc) to Dolby Surround stereo (i.e., 5 channels are matrixed into 2 channels to be decoded to 4 by an external Dolby Pro Logic processor). Both Dolby Digital and MPEG-2 support 2-channel Dolby Surround as the source in cases where the disc producer can't or doesn't want to remix the original onto discrete channels. This means that a DVD labelled as having Dolby Digital sound may only use the L/R channels for surround or "plain" stereo. Even movies with old monophonic soundtracks may use Dolby Digital -- but only 1 or 2 channels.
The downmix process does not include the LFE channel, and may compress the dynamic range in order to improve dialog audibility and keep the sound from becoming "muddy" on average home audio systems. This can result in reduced sound quality on high-end audiosystems. Some players have the option to turn dynamic range compression off. The downmix is auditioned when the disc is prepared, and if the quality is not adequate the audio may be tweaked or a separate L/R Dolby Surround track may be added. Experience has shown that minor tweaking is sometimes required to make the dialog more audible within the limited dynamic range of a home stereo system, but that a separate track is not usually necessary. If surround audio is important to you, you will hear significantly better results from multichannel discs if you have a Dolby Digital system.
Linear PCM is uncompressed (lossless) digital audio, the same format used on CDs. It can be sampled at 48 or 96 kHz with 16, 20, or 24 bits/sample. (Audio CD is limited to 44.1 kHz at 16 bits.) There can be from 1 to 8 channels. The maximum bitrate is 6.144 Mbps, which limits sample rates and bit sizes with 5 or more channels. It's generally felt that the 96 dB dynamic range of 16 bits or even the 120 dB range of 20 bits combined with a frequency response of up to 22,000 Hz from 48 kHz sampling is adequate for high-fidelity sound reproduction. However, additional bits and higher sampling rates are useful in studio work, noise shaping, advanced digital processing, and three-dimensional sound field reproduction. DVD players are required to support all the variations of LPCM, but some of them may subsample 96 kHz down to 48 kHz, and some may not use all 20 or 24 bits. The signal provided on the digital output for external digital-to-analog converters may be limited to less than 96 kHz or less than 24 bits.
Dolby Digital is multi-channel digital audio, compressed using AC-3 coding technology from original PCM with a sample rate of 48 kHz at 16 bits. The bitrate is 64 kbps to 448 kbps, with 384 being the normal rate for 5.1 channels and 192 being the normal rate for stereo (with or without surround encoding). The channel combinations are (front/surround): 1/0, 1+1/0 (dual mono), 2/0, 3/0, 2/1, 3/1, 2/2, and 3/2. The LFE channel is optional with all 8 combinations. For details see ATSC document A/52 http://www.atsc.org/document.html.
MPEG audio is multi-channel digital audio, compressed from original PCM format with sample rate of 48 kHz at 16 bits. Both MPEG-1 and MPEG-2 formats are supported. The variable bitrate is 32 kbps to 912 kbps, with 384 being the normal average rate. MPEG-1 is limited to 384 kbps. Channel combinations are (front/surround): 1/0, 2/0, 2/1, 2/2, 3/0, 3/1, 3/2, and 5/2. The LFE channel is optional with all combinations. The 7.1 channel format adds left-center and right-center channels, but will probably be rare for home use. MPEG-2 surround channels are in an extension stream matrixed onto the MPEG-1 stereo channels, which makes MPEG-2 audio backwards compatible with MPEG-1 hardware (an MPEG-1 system will only see the two stereo channels.)
DTS is an optional multi-channel (5.1) digital audio format, compressed from PCM at 48 kHz. The data rate is from 64 kbps to 1536 kbps. Channel combinations are (front/surround): 1/0, 2/0, 3/0, 2/1, 2/2, 3/2. The LFE channel is optional with all 6 combinations.
SDDS is an optional multi-channel (5.1 or 7.1) digital audio format, compressed from PCM at 48 kHz. The data rate can go up to 1280 kbps.
A DVD-5 with only one surround stereo audio stream (at 192 kbps) can hold over 55 hours of audio. A DVD-18 can hold over 200 hours.
[3.7] How do the interactive features work?
DVD-Video players (and software DVD-Video navigators) support a command set that provides rudimentary interactivity. The main feature is menus, which are present on almost all discs to allow content selection and feature control. Each menu has a still-frame graphic and up to 36 highlightable, rectangular "buttons" (only 12 if widescreen, letterbox, and p&s modes are used). Remote control units have four arrow keys for selecting onscreen buttons, plus numeric keys, select key, menu key, and return key. Additional remote functions may include freeze, step, slow, fast, scan, next, previous, audio select, subtitle select, camera angle select, play mode select, search to program, search to part of title (chapter), search to time, and search to camera angle. Any of these features can be disabled by the producer of the disc.
Additional features of the command set include simple math (add, subtract, multiply, divide, modulo, random), bitwise and, bitwise or, bitwise xor, plus comparisons (equal, greater than, etc.), and register loading, moving, and swapping. There are 24 system registers for information such as language code, audio and subpicture settings, and parental level. There are 16 general registers for command use. A countdown timer is also provided. Commands can branch or jump to other commands. Commands can also control player settings, jump to different parts of the disc, and control presentation of audio, video, subpicture, camera angles, etc.
DVD-V content is broken into "titles" (movies or albums), and "parts of titles" (chapters or songs). Titles are made up of "cells" linked together by one or more "program chains" (PGC). A PGC can be defined as sequential play, random play (may repeat), or shuffle play (random order but no repeats). Individual cells may be used by more than one PGC, which is how parental management and seamless branching are accomplished: different PGCs define different sequences through mostly the same material.
Additional material for camera angles and seamless branching is interleaved together in small chunks. The player jumps from chunk to chunk, skipping over unused angles or branches, to stitch together the seamless video. Since angles are stored separately, they have no direct effect on the bitrate but they do affect the playing time. Adding 1 camera angle for a program roughly doubles the amount of space it requires (and cuts the playing time in half).
 DVD AND COMPUTERS
[4.1] Can I play DVD movies on my computer?
Only if your computer has the right stuff. In addition to a DVD-ROM drive, you must have extra hardware to decode MPEG-2 video and Dolby Digital/MPEG-2/PCM audio. The computer operating system or playback system must support regional codes and be licensed to decrypt copy-protected movies. You may also need software that can read the MicroUDF format used to store DVD data files and interpret the DVD control codes. It's estimated that 10-30% of new computers with DVD-ROM drives will include decoder hardware, and that most of the remaining DVD-ROM computers will include movie playback software. Hardware upgrade kits can also be purchased separately for $400 to $1,000. (OEM price for playback hardware is about $200.)
Note: The recently released QuickTime MPEG Extension for MacOS is for MPEG-1 only and does NOT play MPEG-2 DVD-Video.
Some DVD-Videos and many DVD-ROMs will use video encoded
using MPEG-1 instead of MPEG-2. Many existing computers have MPEG-1 hardware
built in or are able to decode MPEG-1 with software.
CompCore Multimedia and Mediamatics make software to play DVD-Video movies (SoftDVD, DVD Express). Both require at least a 233 MHz Pentium MMX with AGP and an IDE/SCSI DVD-ROM drive with bus mastering DMA support to achieve about 20 frame/sec film rates (or better than 300 MHz for 30 frame/sec video), and can decrypt copy-protected movies (see 1.11). Oak's software requires hardware support. The software "navigators" support most DVD-Video features (menus, subpictures, etc.) and can emulate a DVD-Video remote control.
CompCore, Mediamatics, and Oak Technology have defined standards to allow certain MPEG decoding tasks to be performed by hardware on a video card and the remainder by software. Video graphics controllers with this feature are being called "DVD MPEG-2 accelerated." (The Mediamatics standard is called MVCCA.)
If you have at least a 433 MHz Alpha workstation you'll be able to play DVD movies at full 30 fps in software.
[4.2] What are the features and speeds of DVD-ROM drives?
Most DVD-ROM drives have a seek time of 150-200 ms, access time of 200-250 ms, and data transfer rate of 1.3 MB/s (11.08*10^6/8/2^20) with burst transfer rates of up to 12 MB/s or higher. The data transfer rate from DVD-ROM discs is roughly equivalent to an 9x CD-ROM drive. DVD spin rate is about 3 times faster than CD, so a few DVD-ROM drives read CD-ROM data at 3x speed, but most are 12x or faster. 2x and 3x DVD-ROM drives are already in the works. New 2x DVD-ROM drives (Hitachi, Creative) read CD-ROMs at 20x and 24x speeds.
Connectivity is similar to that of CD-ROM drives: EIDE (ATAPI), SCSI-2, etc. All DVD-ROM drives have audio connections for playing audio CDs. No DVD-ROM drives have been announced with DVD audio or video outputs (which would require internal audio/video decoding hardware).
DVD-ROMs use a MicroUDF/ISO 9660 bridge file system. The OSTA UDF file system will eventually replace the ISO 9660 system of CD-ROMs, but the bridge format provides backwards compatibility until operating systems support UDF.
[4.3] What about recordable DVD-ROM: DVD-R and DVD-RAM?
There are two recordable versions of DVD-ROM: DVD-R (record once) and DVD-RAM (erase and record many times), with capacities of 3.95 and 2.58 G bytes. Both specifications have been published in 0.9 versions and are expected to be finalized in August.
DVD-R uses organic dye polymer technology like CD-R and is compatible with almost all DVD drives. The technology will improve to support 4.7 G bytes in 1 to 2 years, which is crucial for desktop DVD-ROM and DVD-Video production.
DVD-RAM uses phase-change technology and is not compatible with current drives (because of defect managment, reflectivity differences, and minor format differences). New drives compatible with DVD-RAM discs are expected in early 1998. Single-sided DVD-RAM discs will be available with or without cartridges. There are two types of cartridges: type 1 is sealed, type 2 allows the disc to be removed. Double-sided DVD-RAM discs will be available in sealed cartridges only.
Initial price for DVD-R drives is expected to start at about $17,000 and drop within a year to less than $5,000. Initial price for blank DVD-Rs will be $30-$50. DVD-RAM drives will supposedly be introduced for less than $1000, with blank discs at $30-$40 but expected to drop quickly. Disc prices for both DVD-R and DVD-RAM will drop quickly, but DVD-Rs will probably always be cheaper. Pioneer plans to release a commercial DVD-R drive around July. Toshiba originally claimed that its DVD-R drives would be ready in Spring 1997 and that DVD-RAM would be available in Fall 1997. Now they say DVD-R will be available in Summer 1997 and DVD-RAM in March 1998. (Don't hold your breath.)
DVD-R and DVD-RAM are not currently usable for home video recording (see 1.14).
 DVD production
[5.1] How much does it cost to produce a DVD? Isn't DVD much more expensive than videotape, laserdisc, and CD-ROM?
Videotape, laserdisc, and CD-ROM can't be compared to DVD in a straightforward manner. There are basically three stages of costs: production, pre-mastering, and mastering/replication.
DVD production costs are not much higher than for existing media, unless the extra features of DVD-Video such as multiple sound tracks, camera angles, etc. are employed.
Pre-mastering costs are proportionately the most expensive part of DVD. Video and audio must be encoded, menus and control information have to be authored and encoded, it all has to be multiplexed into a single data stream, and finally encoded in low level format. Warner's charges for compression are $120/min for video, $20/min for audio, $6/min for subtitles, plus formatting and testing at about $30/min. A ballpark estimate for producing a two-hour DVD movie is about $30,000. If you want to do pre-mastering yourself, authoring and encoding systems can be purchased from $100,000 to over $2 million. These prices will drop very rapidly in the next few years to where DVDs can be produced on desktop computer systems using additional hardware costing less than $20,000.
Videotapes don't really have a mastering cost, and they run about $2.40 for replication. CDs cost about $1,000 to master and $0.50 to replicate. Laserdiscs cost about $3,000 to master and about $8 to replicate. DVDs currently cost a few thousand dollars to master and about $2.40 to replicate. Since DVD production is based mostly on the same equipment used for CD production, mastering and replication costs will quickly drop to CD levels.
Double-sided or dual-layer discs cost slightly more to replicate, since all that's required is stamping data on the second substrate (and using transparent glue for dual layers). Double-sided/dual-layer discs are more difficult.
[5.2] What DVD authoring systems are available and how much do they cost?
Authoring can also be done by many service bureaus (see below) for around $300/hour.
[5.3] Who can produce a DVD for me?
[A] Authoring (including compression and premastering).
See Robert's DVD Info page http://www.unik.no/~robert/hifi/dvd/ for more pointers.
[5.4] Who can test or verify DVDs?
[6.1] Who invented DVD and who owns it?
DVD is the work of Toshiba, Matsushita, Philips, Sony, and others. There were originally two next-generation standards for DVD. The MMCD format was backed Sony, Philips, and others. The competing SD format was backed by Toshiba, Time Warner, and others. A group of computer companies led by IBM insisted that the DVD proponents agree on single standard. The combined DVD format was announced in September of 1995, avoiding a confusing and costly repeat of the VHS vs. BetaMax videotape battle (or the quadraphonic sound battle of the 1970s).
No single company "owns" DVD. The DVD Consortium now comprises Hitachi, JVC, Matsushita, Mitsubishi, Philips, Pioneer, Sony, Thomson, Time Warner, and Toshiba. (Visit Robert's DVD Info page http://www.unik.no/~robert/hifi/dvd/ for links to company Web pages.)
Any company making DVD products must license the technology, partly from a pool administered by Philips but also separately from Thomson and others. Matsushita licenses the CSS encryption technology free of charge. Macrovision licenses its analog anti-recording technology free of charge to hardware makers, but charges a per-copy royalty to content publishers.
[6.2] Who is making or supporting DVD products?
The following companies have made official statements of products specifically designed for the DVD format.
Studios, video publishers, and distributors:
Computer software titles on DVD-ROM:
At last count (in Feb 1997), there were 139 registered Internet domain names with DVD in them. (Thanks to Robert for this interesting tidbit.)
[6.3] Where can I get more information about DVD?
Here are a few of the top DVD info pages. For more extensive
pointers go to Robert's page, which has all the links you will ever need.
[7.1] Remaining unanswered questions
(If you know the answer to any of these, please speak up!)
[7.2] Notation and units
There's an unfortunate confusion of units of measurement in the DVD world. For example, a single-layer DVD holds 4.7 billion bytes (G bytes), not 4.7 gigabytes (GB). It only holds 4.38 gigabytes. Likewise, a double-sided, dual-layer DVD holds only 15.90 gigabytes, which is 17 billion bytes.
The problem is that "kilo," "mega," and "giga" generally represent multiples of 1,000 (10^3, 10^6, and 10^9), but when used in the computer world to measure bytes they represent multiples of 1,024 (2^10, 2^20, and 2^30).
Most DVD figures are based on 1,000, not 1,024, in spite of using notation such as GB and KB/s. The closest I have been able to get to an unambiguous notation is to use kbps for thousands of bits/sec, Mbps for millions of bits/sec, KB for 1024 bytes, MB for 1,048,576 bytes, and GB for 1,073,741,824 bytes. Feedback on any sort of notation standards would be helpful.
This FAQ is written and maintained by Jim Taylor. The following people have contributed to the FAQ (either directly, by posting to alt.video.dvd, or by me borrowing from their writing :-). Their contributions are deeply appreciated. Information has also been taken from material distributed at the April 1996 DVD Forum.
Robert Lundemo Aas
Originally Created: 04/15/97