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DVD Frequently Asked Questions

In this section of the DVD Place, I've posted Jim Taylor's FAQ. If you want to contact him, the link to his site is on this page. That copy is almost constantly updated, where I'll update this page as I get notice from him. Thanks, and enjoy!!

DVD Frequently Asked Questions (with answers!)

This is the November 5, 1998 revision of the FAQ for the rec.video.dvd Usenet newsgroups. (See below for what's new.)
Please send corrections, additions, and new questions to Jim Taylor <[email protected]>.

Where can I get this FAQ?

Recent significant changes (last posted to newsgroups on Mar 18):

Contents

[1] 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 about half of the 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 recordable variations (DVD-R, DVD-RAM, DVD-RW; see 4.3). Most people expect DVD-ROM to be initially much more successful than DVD-Video. Most new computers with DVD-ROM drives can also play DVD-Videos (see 6.1).

There's also a DVD-Audio format. The technical specifications for DVD-Audio are not yet finalized.

[1.2] What are the features of DVD-Video?

Note: Most discs do not contain all features (multiple audio/subtitle tracks, seamless branching, parental control, etc.), as each feature must be specially authored. Some discs may not allow searching or skipping.

Most players support a standard set of features:

^* Must be supported by additional content on the disc.

Some players 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 generally better than laserdisc (see 2.8.). However, quality depends on many production factors. Until compression experience and technology improves we will occasionally see DVDs that are inferior to laserdiscs. Also, since large amounts of video have already been encoded for Video CD using MPEG-1, a few low-budget DVDs will use that format (which is no better than VHS) instead of higher-quality MPEG-2.

DVD video is compressed from digital studio master tapes to MPEG-2 format. This "lossy" compression removes redundant information (such as areas 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), compression artifacts may be occasionally noticeable. Higher data rates can result in higher quality, with almost no perceptible difference from the master at rates above 6 Mbps. As MPEG compression technology improves, better quality is being achieved at lower rates.

Video from DVD sometimes contains visible artifacts such as color banding, blurriness, blockiness, fuzzy dots, shimmering, missing detail, and even effects such as a face that "floats" behind the rest of the moving picture. It's important to understand that the term "artifact" refers to anything that was not originally present in the picture. Artifacts are sometimes caused by poor MPEG encoding, but artifacts are more often caused by a poorly adjusted TV, bad cables, electrical interference, sloppy digital noise reduction or picture enhancement, poor film-to-video transfer, film grain, player faults, disc read errors, etc. Most DVDs exhibit few visible MPEG compression artifacts on a properly configured system.. If you think otherwise, you are misinterpreting what you see.

Some early DVD demos were not very good, but this is 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. Many demo discs were rushed through the encoding process in order to be distributed as quickly as possible. Contrary to common opinion, and as stupid as it may seem, these demos are not carefully "tweaked" to show DVD at its best. In-store demos should be viewed with a grain of salt, since 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 high-frequency video and causes distortion, just as the treble control set too high for a CD causes it to sound harsh. Many DVD players output video with a black-level setup of 0 IRE (Japanese standard) rather than 7.5 IRE (US standard). On TVs that are not properly adjusted this can cause some blotchiness in dark scenes. 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. Alternatively, audio for most movies is stored as discrete multi-channel surround sound using Dolby Digital or DTS audio compression similar to the surround sound formats used in theaters. As with video, audio quality depends on how well the processing and encoding was done. In spite of compression, Dolby Digital and DTS can be close to or better than CD quality.

The final assessment of DVD quality is in the hands of consumers. Most viewers consistently rate it better than laserdisc, but no one can guarantee the quality of DVD, just as no one should dismiss it based on demos or hearsay. In the end it's a matter of individual perception and the level of quality delivered by the playback system.

[1.4] What are the disadvantages of DVD?

[1.5] What DVD players and drives are 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.

Available players:

Projected player releases:

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 to be available before May. Creative Labs' PC-DVD upgrade kit (Matsushita drive and A/V decoder board; Warner DVD-V sampler) went on sale in the U.S. in April 1997 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) became avilalbe in May 1997, as did Diamond Multimedia's $599 kit. STB Systems DVD Theater Upgrade Kit was be available in July for $699. DynaTek announced a $649 upgrade kit with 6 titles. Toshiba's Infinia DVD-ROM-equipped PC become available Summer 1997. Creative's new "Encore" 2x DVD-ROM kit is available for under $100. Hi-Val's 2nd-generation kit is $380. E4's CoolDVD upgrade kit for Macintoshes became available for $499 in July 1998. Sigma Designs also makes playback cards.
For drive details see http://www.brouhaha.com/~eric/video/dvd/. WebShopper has a good report (dated Sep 16, 1998).

Note: If you buy a player or drive 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] What DVD titles are available?

As with hardware, rosy predictions of hundreds of movie titles for Christmas of 1996 failed to materialize. 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. By April there were over 150 titles in Japan. Movies appeared in the US in March of 1997. Currently (Apr 1998) there are about 800 titles available in the US and over 1200 worldwide. 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. InfoTech predicted over 600 titles by the end of 1997 and more than 8,000 titles by 2000. By December 1997, over 1 million individual DVD discs were shipped.

A concerted launch of DVD hardware and software in Europe is planned for the second quarter of 1998. Over 100 titles are expected to be available by March, with over 250 available by the end of 1998. Time Warner's official launch of DVD in Australia (region 4) is planned for Easter of 1998.

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>. Another extensive list of US titles is at <http://www.surroundfreak.com/dvd/dvd1.htm>. New release lists and announcements are also available at <http://www.image-entertainment.com/laserv.html>. For a list of widescreen-specific DVD titles, visit http://www.WidescreenReview.com>.

Concorde Video released a PAL-format 12 Monkeys in Germany at the end of March 1997. They were threatened by Philips with a lawsuit for not including a multichannel MPEG track, but the issue is now resolved (see 3.6).

DVD-ROM software will slowly appear. Approximately 50% of CD-ROM producers have announced intentions to develop for DVD-ROM. See 6.2 for a list. Many initial DVD-ROM titles are only be available as part of a hardware or software bundle until the market grows larger. IDC expects that 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 high-quality video and multi-channel audio capabilities being added to many DVD-ROM-equipped computers.

[1.7] How much do players and drives cost?

Mass-market DVD movie players currently list for $300 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, and below $150 by 2005.

DVD-ROM drives and upgrade kits for computers sell for around $80 to $600. (OEM drive prices are under $70.) Prices are expected to drop quickly to current CD-ROM drive levels.

[1.8] How much do discs cost?

It varies, but most DVD movies list for $20 to $30 with street prices between $15 and $25, even those with supplemental material. Low-priced movies can be found for under $10. So far DVD has not followed the initial high rental price model of VHS.

DVD-ROMs will initially be slightly more expensive than CD-ROMs since there is more on them, they cost more to replicate, and the market is smaller. But once production costs drop and the installed base of drives grow, DVD-ROMs will cost about the same as CD-ROMs today.

[1.9] How quickly will DVD become established?

Not as fast as generally predicted, but faster than videotape, laserdisc, and CD. By the end of 1997 over 500,000 DVD-Video players shipped worldwide. 349,482 of these were in the US (with about 200,000 actually sold into homes). About ?? DVD video titles were available worldwide, with ?? million copies shipped. About 600 DVD video titles were available in the US, with over 5 million copies shipped and about 2 million sold. Around 330,000 DVD-ROM drives were shipped worldwide with about 1 million bundled DVD-ROM titles. Only 60 DVD-ROM titles were available by the end of 1997, most of them bundled with PCs or drive upgrade kits.

Here are some predictions:

For comparison, there are about 700 million audio CD players and 160 million CD-ROM drives worldwide in 1997. 1.2 billion CD-ROMs were shipped worldwide in 1997 from a base of about 46,000 different titles. There are about 80 million VCRs in the U.S. (89% of households) and about 400 million worldwide. There are about 250 million TVs in the US and 1.2 billion worldwide. Estimated 1997 U.S. sales: 7.7 million VCRs, 900,000 projection televisions.

[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). Also, studios sell distribution rights to different foreign distributors and would like to guarantee an exclusive market. Therefore they have required that the DVD standard include codes that can be used to prevent playback of certain discs in certain geographical regions. Each player is given a code for the region in which it's sold. The player will refuse to play discs that are not allowed in that region. This means that discs bought in one country may not play on players bought in another country.

Regional codes are entirely optional for the maker of a disc. 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 announced that only their new releases will have regional codes, but so far almost all releases play in only one region.

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.
1: Canada, U.S., U.S. Territories
2: Japan, Europe, South Africa, Middle East (including Egypt)
3: Southeast Asia, East Asia (including Hong Kong)
4: Australia, New Zealand, Pacific Islands, Central America, Mexico, South America, Caribbean
5: Former Soviet Union, Indian Subcontinent, Africa (also North Korea, Mongolia)
6: China
(See the map at <http://www.unik.no/~robert/hifi/dvd/world.html>.)

Most players can be modified to play discs regardless of their regional codes. This usually voids the warranty. Some discs, such as those from Buena Vista/Touchstone/Miramax, MGM/Universal, and Polygram contain program code that checks for the proper region. These discs won't play on "code-free" players that have their region set to 0, but they can be played on "code-switchable" players that allow you to change the region using the remote control. Information about modifying players can be found on the Internet and in the rec.video.dvd newsgroups.

Regional codes also apply to DVD-ROM systems, but are allowed for use only with DVD-Video discs, not DVD-ROM discs containing computer software. (See 1.11 below for more details). Computer playback systems check for regional codes before playing movies from a DVD-Video. Most DVD-ROM drives let you change the region code a few times, usually between 5 and 9. Once a drive has reached the limit it can't be changed again unless the vendor or manufacturer resets the drive.

It's likely that regional codes will apply to DVD-Audio.

[1.11] What are the copy protection issues?

There are four forms of copy protection used by DVD:

1) Analog CPS (Macrovision)
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/light cycling. Macrovision creates severe problems for most line doublers. Macrovision is not present on analog component video output of early players, but is required on newer players (AGC only, since there is no burst in a component signal). The discs contain "trigger bits" in the header of each sector telling the player whether or not to enable Macrovision AGC, with the optional addition of 2-line or 4-line Colorstripe. This allows fine control over which sections are copy protected. The producer of the disc decides what amount of copy protection to enable and then pays Macrovision royalties accordingly (a few cents per disc). Just as with videotapes, some DVDs are Macrovision-protected and some aren't. (For a few Macrovision details see SGS/Thomson's NTSC/PAL video encoder datasheets at <http://www.st.com/stonline/books/>.)

2) CGMS
Each disc also contains information specifying if the contents can be copied. This is a "serial" copy generation management system (SCMS) designed to prevent copies or 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 (in the XDS service). The digital standard (CGMS/D) is not yet finalized, but will apply to digital connections such as IEEE 1394/Firewire. See section 4, below.

3) Content Scrambling System (CSS)
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. Some drives may allow the user to reset the region a limited number of times; other drives will self-program after a certain number of movies have been played. 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.

4) Digital Transmission Content Protection (DTCP)
In order to provide for digital connections between components without allowing perfect digital copies, a digital copy protection system has been developed, focused on IEEE 1394/FireWire. The draft proposal (called the 5CP, for "five-company proposal") was made by Intel, Sony, Hitachi, Matsushita, and Toshiba in Feb. 1998. Content is marked with standard CGMS flags of "copy never" or "copy once." Devices that are digitally connected, such as a DVD player and a digital TV, will exchange keys and authentication certificates to establish a channel. The DVD player will encrypt the encoded video signal as it sends it to the receiving device, which must decrypt it. Digital display devices will be able to receive and display all data. Digital recording devices will only be able to receive data which is not marked "copy never," and they must change the CGMS flags to zero copies if the source is marked for one copy. Digital CPS is designed for the next generation of digital TVs and digital video recorders. It will require new DVD players with digital connectors (such as those provided on DV cameras and decks). These new products probably won't appear before mid 1999. Since the encryption is done by the player, no changes are needed to the existing disc format.

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.

The first 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. DTCP is performed by the DVD player, not by the disc developer.

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 they 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).

The Data-Hiding Sub-Group (DHSG) of the DVD Forum's Copy Protection Technical Working Group (CPTWG) received seven watermarking proposals that have since been merged into three: IBM/NEC, Macrovision/Digimarc/Philips, and Hitachi/Pioneer/Sony. Watermarking, which will be added to DVD at some point, permanently marks each digital video frame with noise that is supposedly visually undetectable. Watermark signatures can be recognized by video playback and recording equipment to prevent copying, even when the video is transmitted via digital or analog connections or is subjected to video processing. New players and other equipment will be required to support watermarking. It's possible to make new watermarked discs compatible with existing players, but movie studios will probably not allow it. There are reports that the watermarking technique used by Divx causes visible "raindrop" or "gunshot" patterns.

[1.12] What about DVD-Audio or Music DVD?

The DVD Consortium sought additional input from the music industry before defining the DVD-Audio format. A draft standard was released by DVD Forum's Working Group 4 (WG4) in January 1998. Version 0.9 was released in July, with a final 1.0 version expected in October. See 3.6.1 for details. DVD-Audio products will show up in 1999 at the earliest. Since the DVD-Audio specification includes features or formats not present in the current DVD specification, some DVD-Audio discs will not be playable on current DVD players.
Plea to producers: "Universal players" won't be available for some time, but you can make "universal discs" today. With a small amount of effort, all DVD-Audio discs can be made to work on all DVD players by including a Dolby Digital version of the audio in the DVD-Video zone.
Plea to DVD-Audio authoring system developers: Make your software do this by default or have it strongly recommend this option during authoring.

Sony and Philips are proposing a Super Audio CD format based on Direct Stream Digital (DSD) with sampling rates of up to 100 kHz. SACD will compete with WG4's DVD-Audio proposal. SACD provides "legacy" discs that will have two layers, one that will play in existing CD players, plus a high-density layer for DVD-Audio players. Ironically, initial price for these dual-layer discs will be higher than for a standard CD plus a standard DVD. Sony released version 0.9 of the SACD spec in April 1998. SACD technology will be available to existing CD licensees at no additional cost.

The music industry has requested an "embedding signalling" or "digital watermark" copy protection feature. This uses pit signal processing technology to apply a digital signature and optional encryption keys 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 3.6.2).

[1.13] Which studios are supporting DVD?

When DVD players became available in early 1997, Warner and Polygram were the only major movie studios to release titles. Additional titles were available from small developers. The other studios gradually joined the DVD camp (see 6.2 for a full list, see 1.6 for movie info).

Dreamworks was the last significant studio to announce full DVD support. Paramount, Fox, and Dreamworks initially supported only Divx, but in summer 1998 they each announced support for open DVD.

[1.14] Can 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 DVD-V info, 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 initially will be $30 and up. The first generation of recordable media will hold less than 3/4 as much as prerecorded discs. Realtime compression requires 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, which came out in Sep 1997 for $17,000; or DVD-RAM, which came out in June for around $500; or other recordable variations of DVD (see 4.3). These can record data, but to create full-featured DVD-Videos requires additional hardware and software to do video encoding (MPEG), audio encoding (Dolby Digital, MPEG, or PCM), subpicture encoding (run-length-compressed bitmaps), still frame encoding (MPEG), navigation and control data generation, and multiplexing. And since this can't yet 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 formats. DV (aka DVC) is out already, but decks cost $4,000. D-VHS and other Digital VCR technologies are just becoming available.

[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. There are many schemes for concealing errors in MPEG video, which may be used in future players (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. Major chains such as Blockbuster and West Coast Entertainment rent DVDs in many locations. So far most reports of rental disc performance are positive. A nice list of DVD rental outlets is at <http://home.earthlink.net/~tlfordham/rental.html>.

[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. There are a number of DVD packages such as the "keep case" and Time Warner's "Snapper" that are about as wide as a CD jewel box and about as tall as a VHS cassette box. 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). Many dual-layer discs are currently available (such as Contact, 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" tracks 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. Non-seamless switches cause the video to freeze for less than half a second on most players but up to 4 seconds on some. The "seamlessness" depends as much on the way the disc is prepared as on the design of the player. OTP is also called RSDL (Reverse-Spiral Dual Layer). The advantage of OTP (RSDL) is that longer movies can use higher data rates for better quality than with a single layer. See 1.26 for layer change details.

All DVD players and drives can read 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 hold over 4 hours of video on one side by using two layers. (Early discs used two sides because dual-layer production was not widely supported. This should no longer be a problem.) 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. The MPEG video on DVD is stored in digital format, but it's formatted for one of two mutually incompatible television systems: 525/60 (NTSC) or 625/50 (PAL/SECAM). There are three differences between discs intended for playback on different systems: picture size and pixel aspect ratio (720x480 vs. 720x576), display frame rate (29.97 vs 25), and surround audio (Dolby Digital vs. MPEG). (See 3.4 and 3.6 for details.) Video from film is usually stored at 24 frames/sec but is preformatted for one of the two display rates. Movies formatted for PAL display are usually sped up by 4%, so the audio must be adjusted accordingly before being encoded.

Some players will only play NTSC discs, some players will only play PAL discs, and some will play both. Most European players play both. These multi-standard players output NTSC from a 525/60 disc and PAL from a 625/50 disc. This requires two TVs or a multi-standard TV. 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 no such players have been announced.

A producer can choose to include additional video and audio --at the expense of playing time-- so that all formats are covered. It's unclear if players will be able to automatically recognize and play the correct video track. Of course it's always possible to put 525/60 video on one side of the disc and 625/50 on the other. Most studios so far are including Dolby Digital tracks along with the MPEG audio tracks on their PAL discs.

There are actually three types of DVD players if you count computers. Most DVD playback software and hardware can play both NTSC and PAL 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 the disc be flipped partway through. Most "flipper" discs exist because of producers who are too lazy to optimize the compression or make a dual-layer disc. Better picture quality 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; in 1997 very few DVD plants could make dual-layer discs, but this is no longer the case. No players can automatically switch sides, but it's not needed since most movies less than 4 hours long can easily fit on one dual-layer (RSDL) side.

The following discs are "flippers." (Note: This is not the same as a disc with a widescreen version on one side and a pan & scan version or supplements 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 625/50 (PAL) disc to contain only MPEG audio, but so far MPEG audio is not widely used.

Don't 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. For example, Blazing Saddles and Caddyshack are mono movies, so the Dolby Digital soundtrack on these DVDs has only one channel. Some DVD packaging has small lettering or icons under the Dolby Digital logo that indicates the channel configuration. In some cases, there is more than one Dolby Digital version of a soundtrack: 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 due to oxidation. The large size of laserdiscs makes them flexible, so that movement along the bond between sides can break the seal. Like laserdiscs, DVDs are made of two platters glued together, but DVDs are more rigid and use newer adhesives. 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 to it 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>. A list of anamorphic titles is available at <http://www.laserviews.com/16x9.html>.

[1.26] How do I make the subtitles on my Pioneer player go away?

On the remote control, press Subtitle, then either Clear or 0 (zero). No need to use the menus.

[1.27] What is a layer change? Where is it on specific discs?

Some movies over 2 hours long may be spread across two layers on a disc. When the player changes to the second layer, the video and audio may freeze for a moment. The length of the pause depends on the player and on the layout of the disc. The pause is not a defect in the player or the disc. See 1.18 for details.

Layer changes on RSDL discs:

[1.28] The disc says Dolby Digital. Why do I get 2-channel surround audio?

Some discs (many from Columbia TriStar) put 2-channel Dolby Surround audio on track one and 5.1-channel audio on track two. Unless you intervene, the player will play the default 2-channel track. Use the audio button on the remote or select the 5.1 track from the menu. (Note: The Sony 3000 has a feature to automatically select the first 5.1 track.)

Dolby Digital doesn't necessarily mean 5.1 channels. See 3.6.

[1.29] Why doesn't the repeat A-B feature work on some discs?

Almost all features of DVD such as search, pause, and scan can be disabled by the disc, which can prevent the operation the player needs to back up and repeat a segment. If the player uses time search to repeat a segment, then a disc with fancy non-sequential title organization may also block the repeat feature. In many cases the authors don't even realize they have prevented the use of this feature.

[1.30] What's the difference between first, second, and third generation DVD?

There is no answer to this question, since you’ll get a different response from everyone you ask. According to some people, second-generation DVD players came out in the fall of 1997 and third-generation players are those that came out in the beginning of 1998. According to others, the second generation of DVD will be "high-definition" players (see 2.9) that won't come out until 2003 or so. There are many confusing variations between these extremes, including the viewpoint that DTS-compatible players or Divx players constitute the third generation.

Things are a little more clear cut on the PC side, where second generation usually means 2x DVD-ROM drives that can read CD-Rs, and third generation usually means DVD-ROM drives that can read DVD-RAMs.

[1.31] What's a hybrid DVD?

Hah, hah, hah! Do you really want the answer to this one? Ok, you asked for it…

1. A disc that works in both DVD-Video players and DVD-ROM PCs. (More accurately called a multizone DVD, but probably the most common use of the term hybrid.)
2. A DVD-ROM disc that runs on Windows and Mac OS computers. (More accurately called a cross-platform DVD.)
3. A DVD-ROM or DVD-Video disc that also contains Web content for connecting to the Internet (More accurately called a WebDVD or Web-connected DVD.)
4. A disc that contains both DVD-Video and DVD-Audio content.
5. A disc with two layers, one that can be read in DVD players and one that can be read in CD players. (More accurately called a legacy or sandwich disc.)
6. A disc with two layers, one containing pressed (DVD-ROM) data and one containing rewritable (DVD-RAM) media for recording and re-recording. (More accurately called a mixed-media or rewritable sandwich disc.)

Did I miss anything?

[1.32] What's the deal with DTS and DVD?

Digital Theater Systems Digital Surround is an audio encoding format similar to Dolby Digital. It requires a decoder, either in the player or in an external receiver. See 3.6.2 for technical details. Some people claim that because of its lower compression level DTS sounds better than Dolby Digital. Others claim there is no meaningful difference. DTS discs are produced only by DTS, under license from movie studios, and are generally considered to be specialty items intended for audio enthusiasts. It's expected that discs produced by DTS will also be available in standard DVD format.

DTS is an optional format on DVD. The original DVD specification developed in 1996 provides an ID code for DTS, but players made before mid 1998 (and many since) ignore DTS tracks. A few demo discs were created by embedding DTS data into a PCM track (the same technique used with CDs and laserdiscs), and these are the only DTS DVD discs that work on all players. New DTS-compatible players arrived in mid 1998, but official DTS discs using the DTS audio stream ID specified by the DVD-Video standard apparently will not appear until 1999 (they were originally scheduled to arrive in time for Christmas 1997). DTS-compatible players will carry an official "DTS Digital Out" logo. A few manufacturers may provide upgrades to make existing players compatible with DTS discs.

Dolby Digital or PCM audio are required on 525/60 (NTSC) discs, and since both PCM and DTS together don't usually leave enough room for quality video encoding, essentially every disc with a DTS soundtrack will also carry a Dolby Digital soundtrack. This means that all DTS discs will work in all DVD players, but a DTS-compatible player and a DTS decoder are required to play the DTS soundtrack. DTS audio CDs will work on all DVD players, since the DTS data is encapsulated as standard PCM tracks that are passed untouched to the digital audio output(s).

[2] DVD's relationship to other products

[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:
[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 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?

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 common solution is to use two lasers at different wavelengths: one for reading DVDs and the other for reading CDs and CD-Rs. Variatons on the theme include Sony's "dual discrete optical pickup" with switchable pickup assemblies with separate optics, 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. Look for drives with the MultiRead label, which guarantees compatibility with CD-R and CD-RW media.

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

[2.4.4] Is CD-RW compatible with DVD?

Usually. CD-Rewritable (Orange Book Part III) has a lower reflectivity difference, requiring new automatic-gain-control (AGC) circuitry. CD-RW discs can't be read by most existing CD-ROM drives and CD players. The new "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).

[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. Panasonic, RCA, Samsung, and Sony models play Video CDs. Japanese Pioneer models play Video CDs but American models don't. Toshiba players other than the new model 2100 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 apparently scale all 288 lines 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 Super Video CD compatible with DVD?

Not currently. 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 480x567 resolution) and 2-channel MPEG-2 Layer II audio. As with DVD, it can overlay graphics for subtitles. Since it's technically easy to make a DVD-Video player compatible with SVCD, it will probably happen soon, but perhaps only on Asian DVD player models. It's not likely that SVCD will be released outside of China and nearby countries.

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

[2.4.7] 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.

[2.4.8] 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).

[2.4.9] 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 may be a problem with DVD-ROM drivers skipping track zero (as has been the case with some new CD-ROM drivers).

[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 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.

[2.4.12] Is MP3 compatible with DVD?

No. MP3 is MPEG-1 Layer 3 audio compression. (MP3 is not MPEG-3.) The DVD-Video spec allows Layer 2 only. MP3 can be played on a computer with a DVD-ROM drive, but not in a DVD-Video player.

[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 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 (on Sep. 7, 1998, Pioneer's president Kaneo Ito said the company expects laserdisc products to be in the market for another one-and-half to two years). 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 will be available in late 1998 or early 1999 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 for more information on DVD and HDTV.

The final 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, laserdisc was hurt by anticipation of DVD before it even came out. In 1996 laserdisc player sales were down 37% even though sales of VCRs and hi-fi/surround systems were up. The silver lining in this cloud is that disc prices came down. (Laserdisc movie sales were only down 2.5% in 1996.)

[2.7] How does DVD compare to laserdisc?

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 Leopold's FAQ at <http://www.cs.tut.fi/~leopold/Ld/FAQ/index.html>, and Bob Niland's FAQs and overview at <http://www.frii.com/~rjn/laser/> (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.

DVD-Video does not directly support HDTV. No 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. DVD does use the same 16:9 aspect ratio and Dolby Digital audio format of HDTV.

HDTV in the US is part of the new DTV format, which includes both high definition (HD) and standard definition (SD). The resolution and frame rates of DTV in the US will generally correspond to the ATSC recommendations for SD (704x480 at 24P, 30P, 60I, 60P) and HD (1280x720 at 60P and 1920x1080 at 30P). (24P means 24 progressive frames/sec, 60I means 60 interlaced 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. 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 sets will become available in late 1998 or early 1999 at very high prices (about $8000 and up). It will take many years before even a small percentage of homes have HDTV sets. CEMA expects 10 percent of U.S. households to have HDTV in 2003, 20 percent by 2005, and 30 percent by 2006.

HTDV sets will 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 (YCrCb) or 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.

Eventually the DVD-Video format will be upgraded to a "DVD-HD" format, probably around 2003 at the earliest, based on higher-capacity discs and blue or purple lasers (already demonstrated by many DVD manufacturers). New DVD-HD players will play current DVD discs and will make them look even better, but new DVD-HD discs won't be playable in older DVD players. Ironically, DVD-ROM computers will support HDTV before DVD-Video players, since 2x drives coupled with appropriate playback and display hardware meet the 19 Mbps data rate needed for HDTV.

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 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.

[2.10] What's Divx?

Depending on whom you ask, Divx (formerly ZoomTV) is 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 that lets you get cheap discs almost anywhere and keep them for later viewings. Regardless, Divx will confuse consumers and delay the acceptance of DVD. Developed by Circuit City and a Hollywood law firm, Divx was announced for Summer 1998 release, which means players and discs probably won't be available until Fall of 1998. Disney (Buena Vista), Twentieth Century Fox, Paramount, Universal, MGM, and DreamWorks SKG will release Divx discs. (All of these studios are also releasing open DVDs.) JVC, Matsushita (Panasonic), Pioneer, Thomson (RCA/Proscan/GE), and Zenith (which just entered Chapter 11) are developing Divx players. The studios and hardware makers supporting Divx have been offered incentives totalling over $110 million.

Divx is a pay-per-viewing-period variation of DVD. Divx discs will be sold for $4.50. Once inserted into a Divx player the disc will 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" must pay $3.25 to unlock it for another 48 hours. A Divx DVD player, which costs about $100 than a regular player, must be hooked up to a phone line so it can call an 800 number for about 20 seconds during the night once each month to upload billing information. Special Divx Silver discs can be permanently unlocked by paying a higher fee (usually $20), and unlimited-playback Divx Gold discs may also be offered for sale at a price similar to regular "open" DVDs. Divx players 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 and triple DES encryption (three 56-bit keys). No computer support of Divx has been announced, and in any case special decryption hardware would be required since DES is too complex for realtime software decoding. Because of the DES encryption, Divx technology may not be allowed outside the U.S.

Divx trials began June 8, 1998, in San Francisco, CA and Richmond, VA. The only available player was from Zenith (which is in Chapter 11 bankruptcy), and the promised 150 movies had somehow dwindled to 14. The limited nationwide rollout (with one Zenith player model and 150 movies in 190 stores) began on September 25, 1998.

Advantages of Divx:

Disadvantages of Divx:

For more information, see the Divx FAQ at <http://www.divx.com> and the Anti Divx page at <http://www.dvdresource.com/divx>.

[3] DVD technical details

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

Most DVD players have the following output connections:
Video:
- Composite video (CVBS) RCA (NTSC or PAL)
- Y/C (s-video) (NTSC or PAL)
Audio:
- Dual RCA stereo analog audio (with Dolby Surround encoding)
- Digital audio (IEC-958 Type II RCA coax [S/P DIF] or EIAJ CP-340 optical [Toslink]). Raw digital audio (AC-3, MPEG-2, PCM, or optional DTS or SDDS) requires an external decoder or an amplifier/receiver with built-in decoder. (Note: The digital AC-3 audio output is not the same as the RF AC-3 output on laserdisc players.)

Some players may have additional connections:
- Component interlaced analog video, NTSC or PAL (YUV: 3 RCA connectors, RGB: SCART connector or 3 RCA).
- Component progressive analog video, NTSC or PAL (YUV, 3 connectors). (Toshiba SD7108)
- RF video output for connecting via channel 3 or 4 to TV without direct input. (Panasonic DVD-A300, RCA 5500P)
- 6 RCA jacks for analog surround sound output. (Panasonic DVD-A300, RCA 5500P, Samsung DVD905)
- AC-3 RF output on combo LD/DVD players. LD AC-3 on RF output only, DVD AC-3 on coax/optical outputs only. (Pioneer DVL-90, DVL-700)

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 Midiman C02.

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. A $700 converter is available from avscience, and $900 converter, the CVC 100, is available from Extron.

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.

Video

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.

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.

Audio

Note: All DVD players have either a built-in Dolby Digital (AC-3) or MPEG audio decoder, or both. 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. Most players have only a 2-channel-output decoder, but some provide 6-channel output (details below).

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

It's generally not a good idea to route the video from your DVD player through your VCR. Most movies use Macrovision protection, which will cause problems such as a repeated darkening and lightening of the picture. See 1.11 and the Video RF section of 3.2 and for more info.

[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 0.68G 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). (See note in section 7.2.)

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 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 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 produce 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-structured MPEG pictures, with interlaced field-encoded macroblocks used only when needed for motion. On a computer, which is not tied to the display refresh rate, the repeat_first_field flags can be mostly ignored and the video can be 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. Most film source is encoded progressive; 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 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. 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 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-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 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.

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. Unfortunate note: DVD Closed Caption MPEG-2 storage format is slightly different than the ATSC format.

[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 can output video in four different ways:

Letterbox (often abbreviated to LBX) means the video is shown in its theatrical aspect ratio, usually 1.85:1 or 2.40:1. Since this is wider than standard 4:3 TV, black bars must be added to the top and bottom. Pan & scan means the smaller TV "window" is panned and zoomed around the wider movie picture, chopping off the sides. However, most movies are shot soft matte, which means the full TV-sized film frame is used, with the top and bottom masked off in the theater. When transferred to video, the extra picture on the film can be included during the pan & scan process. For more details and nice visual aids see Leopold's "How Film Is Transferred to Video" page, <http://www.cs.tut.fi/~leopold/Ld/FilmToVideo>. A list of movie aspect ratios is at <http://cheezmo.com/wsmc>.

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 have been 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 form.

Anamorphic (16:9) video can be displayed on widescreen equipment, which stretches the video back out to its original width. Alternatively, many new European standard TV's can reduce the vertical scan area to restore the proper aspect ratio without losing resolution (an automatic trigger signal is sent on SCART pin 8). If anamorphic video is shown unchanged on a standard 4:3 display, people will look tall and skinny as if 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, many 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.

The Laserviews Web site has a list of anamorphic DVD titles.

Anamorphic video can also be converted by the player for display on standard 4:3 TVs in letterbox or pan & scan form. The conversion options available for each disc are determined by the producer of the disc. So far no discs have been released with auto letterbox option (partly because equipment for storing the picture shift information is not widely available).

For automatic letterbox mode, the player 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 using a "letterbox filter" that combines 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. Some players have better letterbox filters than others, using weighted averaging to combine lines (scaling 4 lines into 3 or merging the 3rd and 4th lines) rather than simply dropping one out of every four lines.

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 a "center of interest" offset that's 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, many DVD producers choose to put a separate pan & scan version on the disc in addition to the widescreen version.

Anamorphosis causes no problems with line doublers and other video scalers, which simply duplicate the scan 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:
- 4:3 full frame
- 4:3 LB (for automatically setting letterbox expand mode on widescreen TV)
- 16:9 LB only (player not allowed to pan & scan on 4:3 TV)
- 16:9 PS only (player not allowed to letterbox on 4:3 TV)
- 16:9 LB or PS (viewer can select pan & scan or letterbox on 4:3 TV)

[3.6] What are the audio details?

When DVD was first released in 1996 there was no defined DVD-Audio format, although the audio capabilities of the DVD-Video format far surpass CD-ROM. The DVD-Audio 1.0 specification has been finalized and will be released in October of 1998.

[3.6.1] DVD-Audio details

LPCM is mandatory, with up to 6 channels at sample rates of 48/96/192 kHz (also 44.1/88.2/176.4 kHz) and sample sizes of 16/20/24 bits. This allows theoretical frequency response of up to 96 kHz and dynamic range of up to 144 dB. Multichannel PCM will be downmixable by the player, although at 192 and 176.4 kHz only two channels are available. The maximum data rate is 9.6 Mbps.

The WG4 decided to include lossless compression (it's about time!), and on August 5, 1998 approved Meridian's MLP (Meridian Lossless Packing) scheme, already licensed by Dolby. MLP will allow playing times of about 74 to 135 minutes of 6-channel 96kHz/24-bit audio on a single layer (compared to 45 minutes without packing). Two-channel 192kHz/24-bit playing times will be about 120 to 140 minutes (compared to 67 minutes without packing).

Other audio formats of DVD-Video (described below) are optional on DVD-Audio discs. A subset of DVD-Video features (no angles, no seamless branching, etc.) is included for DVD-Audio. It's expected that shortly after DVD-Audio players appear, new DVD-Video players will also support all DVD-Audio features.

Sony and Philips are promoting a competing format based on DSD. See 1.12 for more info.

[3.6.2] Audio details of DVD-Video

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. Some DVD-Video discs contain mostly audio with only video still frames.

A DVD-Video disc can have up to 8 audio tracks (streams). Each track can be in one of three formats:

Two additional optional formats are provided: DTS and SDDS. Both require external decoders and are not supported by all players.

The ".1" refers to a low-frequency effects (LFE) channel that connects to a subwoofer. This channel carries an emphasized bass audio signal.

Linear PCM is uncompressed (lossless) digital audio, the same format used on CDs and most studio masters. 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 and less than 24 bits.

Dolby Digital is multi-channel digital audio, using lossy AC-3 coding technology from original PCM with a sample rate of 48 kHz at up to 24 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). (Most Dolby Digital decoders support up to 640 kbps.) 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>. Dolby Digital is the format used for audio tracks on almost all DVDs.

MPEG audio is multi-channel digital audio, using lossy compression 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.) MPEG Layer III (MP3) and MPEG-2 AAC (aka NBC, aka unmatrix) are not supported by the DVD-Video standard.

DTS (Digital Theater Systems) Digital Surround is an optional multi-channel (5.1) digital audio format, using lossy compression from PCM at 48 kHz at up to 20 bits. The data rate is from 64 kbps to 1536 kbps (though the DTS Coherent Acoustics format supports up to 4096 kbps for lossless compression). 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. The DVD standard includes an audio stream format reserved for DTS, but many players ignore it. According to DTS, existing DTS decoders will work with DTS DVDs. All DVD players can play DTS audio CDs. See 1.32 for general DTS information. For more info visit <http://www.dtstech.com>.

SDDS (Sony Dynamic Digital Sound) 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. SDDS is a theatrical film soundtrack format based on the ATRAC compression format that is also used by Minidisc. Sony has not announced any plans to support SDDS on DVD.

THX (Tomlinson Holman Experiment) is not an audio format. It's simply an additional set of processes applied by THX-certified surround sound amplifiers. "THX 4.0" processing is added to Dolby Pro Logic: crossover sends bass from front channels to subwoofer; re-equalization on front channels; timbre matching on rear channels; decorrelation of rear channels; bass curve that emphasizes low frequencies. "THX 5.1" processing is added to Dolby Digital and improves on 4.0: rear speakers are now full range, so crossover sends bass from both front and rear to subwoofer; decorrelation is turned on automatically when rear channels have the same audio, but not during split-surround effects, which don't need to be decorrelated.

Discs containing 525/60 video (NTSC) must use PCM or Dolby Digital on at least one track. Discs containing 625/50 video (PAL/SECAM) must use PCM or MPEG audio or Dolby Digital on at least one track. Additional tracks may be in any format. A few first-generation players, such as those made by Matsushita, can't output MPEG-2 audio to external decoders.

The original spec required either MPEG audio or PCM on 625/50 discs. There was a brief scuffle led by Philips when early discs came out with only two-channel MPEG and multichannel Dolby Digital, but the DVD Forum clarified in May 1997 that only stereo MPEG audio was mandatory for 625/50 discs. In December 1997 the lack of MPEG-2 encoders (and decoders) was a big enough problem that the spec was revised to allow Dolby Digital as the only audio track on 625/50 discs.

For stereo output (analog or digital), all players have a built-in 2-channel Dolby Digital decoder that 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). PAL players also have an MPEG or MPEG-2 decoder. 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. Sony players can optionally downmix to non-surround stereo.

The Dolby Digital downmix process does not usually 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 audio systems. Some players have the option to turn off the dynamic range compression. The downmix is auditioned when the disc is prepared, and if the result is not acceptable 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.

All five audio formats support karaoke mode, which has two channels for stereo (L and R) plus an optional guide melody channel (M) and two optional vocal channels (V1 and V2).

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.

Many people complain that the audio level from DVD players is too low. In truth the audio level is too high on everything else. Movie soundtracks are extremely dynamic, ranging from near silence to intense explosions. In order to support an increased dynamic range and hit peaks (near the 2V RMS limit) without distortion, the average sound volume must be lower. This is why the line level from DVD players is lower than from almost all other sources. And so far, unlike on CDs and LDs, the level is much more consistent between discs.

[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 pan & scan 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 needed (and cuts the playing time in half).

[4] 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, or your computer must be fast enough to do the decoding in software. Decent software-only playback requires a 300-MHz Pentium II or Mac G3. The computer operating system or playback drivers must support regional codes and be licensed to descramble copy-protected movies. You'll need a player application that provides an interface for controlling the disc. You may also need software that can read the MicroUDF format used to store DVD data files. 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 decoder software. Hardware upgrade kits can be purchased for existing computers (usually minimum 133 MHz Pentium), starting at $350. See <http://www.brouhaha.com/~eric/video/dvd> for a list of drives and upgrade kits.

Unfortunately, even though computers have the potential to produce better video than settop DVD-Video players by using progressive display and higher scan rates, current systems don't look as good as a home player hooked up to a quality TV.

Microsoft Windows 98 includes DirectShow 5.2, which provides standardized support for DVD-Video and MPEG-2 playback. (DirectShow can also be installed in Windows 95.) Windows NT 4.0 doesn't support DVD-Video well at all, but NT 5.0 will use the same DirectShow drivers as Windows 98. Apple QuickTime 3.0 is partially ready for DVD-Video and MPEG-2 but does not yet have software decoding support in place.

Note: The QuickTime MPEG Extension for MacOS is for MPEG-1 only and does NOT play MPEG-2 DVD-Video.

Some DVD-ROMs and a few DVD-Videos use video encoded using MPEG-1 instead of MPEG-2. Most recent computers have MPEG-1 hardware built in or are able to decode MPEG-1 with software.

Mediamatics (DVD Express), Xing, Zoran (SoftDVD) and others make software to play DVD-Video movies. All require at least a 233 MHz Pentium II with AGP and an IDE/SCSI DVD-ROM drive with bus mastering DMA support to achieve about 20 frame/sec film rates, or require better than 350 MHz for 30 frame/sec video. Oak's software requires the Creative Dxr2 hardware decoder. These software players support most DVD-Video features (menus, subpictures, etc.) and can emulate a DVD-Video remote control.

Zoran, 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 100-200 ms, access time of 150-250 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 a 9x CD-ROM drive. DVD spin rate is about 3 times faster than CD, but almost all DVD-ROM drives increase the speed when reading CD-ROMs, achieving 12x or faster performance. 2x DVD-ROM drives are available (providing a transfer rate of 22.2 Mbps or 2.6 MB/s from DVDs, equivalent to an 18x CD-ROM rate) and 5x drives have been announced, although they don't achieve a true sustained transfer rate of 5x (55.4 Mbps). Most 2x DVD-ROM drives read CD-ROMs at 20x (max) speeds and higher, and most 5x drives read CD-ROMs at 32x (max).

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: DVD-R, DVD-RAM, DVD-RW, and +RW?

There are three recordable versions of DVD-ROM: DVD-R, DVD-RAM, and DVD-RW. DVD-R can record data once (sequentally only), while DVD-RAM and DVD-RW can be rewritten hundreds of thousands of times. Final versions of the DVD-R and DVD-RAM specifications were published in August 1997 (see 6.1). DVD-RW will be finalized by the end of 1998. These recordable media are not currently usable for home video recording (see 1.14), though home DVD-RAM recorders will eventually become available.

DVD-R

DVD-R uses organic dye polymer technology like CD-R and is compatible with almost all DVD drives. Initial capacity is 3.95 billion bytes, but will be extended to 4.7 billion bytes around mid 1999, which is crucial for desktop DVD-ROM and DVD-Video production.

Pioneer released DVD-R drives in October 1997 (about 6 months late) for $17,000. The price will probably drop to less than $5,000 for the new 4.7G drives that combine DVD-R and DVD-RW. Price for blank DVD-Rs is about $50. Blank media is being made by Hitachi Maxell, Mitsubishi, Mitsui, Pioneer, and TDK.

The advantages of DVD-R and DVD-RW drives, which are used primarily for DVD production, are higher capacity and compatibility with almost all DVD players and drives. Matsushita, Taiyo Yuden, Mitsubishi, and Hitachi Maxell have all announced research into 4.7-billion-byte DVD-R media. These are not competing DVD-R formats, merely manufacturing advances that allow higher density.

DVD-R discs are expected to last anywhere from 50 to 300 years, about as long as CD-R discs. See <http://www.ee.washington.edu/conselec/CE/kuhn/otherformats/95x9.htm> for more info.

DVD-RAM

DVD-RAM, with an initial storage capacity of 2.58 billion bytes, uses phase-change (PD) technology with some MO features mixed in and is not compatible with current drives (because of defect management, reflectivity differences, and minor format differences). A wobbled groove is used to provide clocking data, with marks written in both the groove and the land between grooves. The grooves and pre-embossed sector headers are molded into the disc during manufacturing. Single-sided DVD-RAM discs come with or without cartridges. There are two types of cartridges: type 1 is sealed, type 2 allows the disc to be removed. Discs can only be written while in the cartridge. Double-sided DVD-RAM discs will be available in sealed cartridges only. Cartridge dimensions are 124.6mm x 135.5mm x 8.0mm. Future DVD-RAM discs may use a contrast enhancement layer and a thermal buffer layer to achieve higher density. Hitachi has announced reaching 4.7 billion bytes by reducing mark size from 0.41/0.43 microns to 0.28/0.30 microns and track pitch from 0.74 microns to 0.59 microns.

DVD-RAM drives appeared in June 1998 (about 6 months late) for around $500, with blank discs at about $30for single-sided and $45 for double-sided. Disc prices were under $20 by August 1998. The first DVD-ROM drive that can read DVD-RAM discs is being released by Panasonic in September 1998 (SR-8583, 5x DVD-ROM, 32x CD).

DVD-RW

DVD-RW (formerly DVD-R/W, formerly DVD-ER) is a phase-change erasable format that will be available around the middle of 1999. Developed by Pioneer based on DVD-R, using the similar track pitch, mark length, and rotation control, DVD-RW will be playable in most DVD drives and players. (Some drives and players are confused by DVD-RW media's lower reflectivity into thinking its a dual-layer disc. Simple firmware upgrades will be required to solve the problem.) DVD-RW uses groove recording with address info on land areas for synchronization at write time (land data is unnecessary during reading). Initial capacity will be 4.7 billion bytes.

+RW

Phase-Change Rewritable, originally called DVD+RW and later changed to +RW under pressure from the DVD Forum, is a competing erasable format announced by Philips, Sony, Hewlett-Packard and others based on DVD and CD-RW technology. +RW drives will read DVD-ROMs and CDs, but will not be compatible with DVD-RAM. Minor changes to DVD-ROM drives will allow them to read +RW discs. +RW, which holds 2.8 gigabytes (3G) uses phase-change technology with wobbled groove and either CLV format for sequential video access (read at CAV speeds by drive) or CAV format for random access. +RW will not be ready for production until late 1998 at the earliest, and its backers claim it will be used only for computer data, not home video. Second-generation +RW drives will write CD-Rs and CD-RWs.

Others

Other upcoming potential competitors to DVD-RAM include AS-MO (formerly MO7), which holds 5 to 6 billion bytes, and NEC's MMVF (Multimedia Video Format), which holds 5.2 billion bytes and is targeted at home recording. Both are expected to read DVD-ROM (and DVD-R) but not DVD-RAM or +RW. MMVF is similar to DVD-RW and +RW, using two bonded 0.6mm phase-change substrates, land and groove recording, and a 640nm laser.

[5] DVD production

DVD production has two phases: development and replication. These are different depending on whether you're making a DVD-ROM or a DVD-Video.

DVD-ROMs can be developed with traditional software development tools such as Macromedia Director, Asymetrix Toolbook, HyperCard, Quark mTropolis, and C++. Discs, including DVD-R check discs, can be created with UDF formatting software (see 5.3). DVD-ROMs that take advantage of DVD-Video's MPEG-2 video and multichannel Dolby Digital or MPEG-2 audio require video and audio encoding (see 5.3).

DVD-Video development has three basic parts: encoding, authoring (design, layout, and testing), and premastering (formatting a disc image). The entire development process is sometimes referred to as authoring. Development facilities are provided by many service bureaus (see 5.5). If you intend to produce numerous DVD-Video titles (or you want to set up a service bureau), you may want to invest in encoding and authoring systems (see 5.3 and 5.4).

Replication (including mastering) is usually a separate job done by large plants that also replicate CDs (see 5.5). DVD replication equipment typically costs millions of dollars. Most replication plants provide "one-off" or "check disc" services, where one to a hundred discs are made for testing before mass duplication.

[5.1] How much does it cost to produce a DVD? Isn't it 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 (authoring, encoding, and formatting), 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 $20,000. If you want to do pre-mastering yourself, authoring and encoding systems can be purchased at prices from $50,000 to over $2 million. These will drop very rapidly in the next few years to where DVDs can be produced on a desktop computer system that costs 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. As of July 1998, DVDs cost about $2000 to master and about $1.70 to replicate. Since DVD production is based mostly on the same equipment used for CD production, mastering and replication costs will drop to CD levels. Pre-mastering costs are mostly for authoring systems and encoding systems which cost tens of thousands of dollars, but these too will get much cheaper in the next few years.

Double-sided or dual-layer discs cost only a little 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 (DVD-18s) are more difficult and not yet commercially available.

[5.2] What DVD-ROM formatting tools are available?

[5.3] What video and audio encoding tools are available?

Video

Audio

[5.4] What DVD-Video authoring systems are available?

[5.5] Who can produce a DVD for me?

[A] Authoring (including encoding and premastering).
[R] Replication (mastering and/or one-offs).

See Robert's DVD Info page <http://www.unik.no/~robert/hifi/dvd/> for more pointers.

[5.6] Who can test or verify DVDs?

[6] Miscellaneous

[6.1] Who invented DVD and who owns it? Whom to contact for specifications and licensing?

DVD is the work of Matsushita, Toshiba, 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, Matsushita, 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 standard was developed by a consortium of 10 companies: Hitachi, JVC, Matsushita, Mitsubishi, Philips, Pioneer, Sony, Thomson, Time Warner, and Toshiba. Working groups with representatives from many other companies also contributed. In May 1997 the Consortium was replaced by the DVD Forum, which is open to all companies (more info at <http://www.dvdforum.com>). Visit Robert's DVD Info page <http://www.unik.no/~robert/hifi/dvd/> for links to Web pages of companies working with DVD.)

The official DVD specification books are available from Toshiba after signing a nondisclosure agreement and paying a $5000 fee. Contact Toshiba DVD Products 1-1 Shibaru 1-Chome, Minato-ku, Tokyo 105-01, Japan, 81-3-3457-2473, fax 81-3-5444-9401. ECMA has developed international standards for DVD-ROM (the smallest part of the DVD spec), available for free download as ECMA-267 and ECMA-268 from www.ecma.ch. ECMA has also standardized DVD-RAM in ECMA-272 and ECMA-273, and +RW as ECMA-274 (see 4.3). The UDF file system used by DVD is available from www.osta.org.

Any company making DVD products must license the patented technology from a Philips/Pioneer/Sony pool, a Hitachi/Matsushita/Mitsubishi/Time Warner/Toshiba/Victor pool, and from Thomson. Total royalties are about 5% for a DVD-Video player, $6 for a DVD-ROM drive and decoder, and 10 cents for a DVD disc. Matsushita licenses the CSS encryption technology free of charge; contact CSS Interim License Organization, 2-15 Matsuba-cho, Kadoma, Osaka 571 Japan, 81-6-905-4155, fax 81-6-901-9299. Macrovision licenses its analog anti-recording technology free of charge to hardware makers, but charges a per-copy royalty to content publishers. The DVD format and logo must also be licensed; contact Toshiba DVD Business Promotion and Support: 81-3-5444-9580, fax 81-3-5444-9430. An MPEG-2 patent license may also be required, from MPEG LA (Licensing Adminstrator). Cost is about $4 for a DVD player or decoder card and 4 cents for each DVD disc, although there seems to be disagreement on whether content producers owe royalties for discs. Contact MPEG LA for more info: <http://www.mpegla.com>.

[6.2] Who is making or supporting DVD products?

The following companies have made official statements of products specifically designed for the DVD format.

Consumer electronics:

Studios, video publishers, and distributors:

A list of studio addresses is available at <http://www.high-rez.com/contacts.htm>

Computer hardware/software:

Computer software titles on DVD-ROM:

[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.

You might also want to take a look at the book DVD Demystified, by the author of this FAQ. More info at <http://www.videodiscovery.com/dvd>.

[7] Leftovers

[7.1] 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 1000 (10^3, 10^6, and 10^9), but when used in the computer world to measure bytes they generally represent multiples of 1024 (2^10, 2^20, and 2^30). Both Windows and Mac OS list volume capacities in "true" megabytes and gigabytes, not millions and billions of bytes

Most DVD figures are based on multiples of 1000, in spite of using notation such as GB and KB/s that traditionally have been based on 1024. The "G bytes" notation does seem to consistently refer to 10^9. 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, "kilobytes" for 1024 bytes, "megabytes" for 1,048,576 bytes, and "gigabytes" for 1,073,741,824 bytes.

[7.3] Acknowledgments

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, May 1997 DVD-R/DVD-RAM Conference, and October 1998 DVD Forum Conference.

Robert Lundemo Aas
David Boulet
Espen Braathen
Wayne Bundrick
Roger Dressler
Chad Fogg
Dwayne Fujima
Robert "Obi" George
Henrik "Leopold" Herranen
Irek Defee
Kilroy Hughes
Ralph LaBarge
Martin Leese
Dana Parker
Eric Smith
Steve Tannehill
Geoffrey Tully

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