Special thanks to Bob Niland (rjn@csn.org), whose work makes up a large portion of this FAQ.
Also thanks to David Uy (duy@unity.ncsu.ed), Phil Kim (kimp@rpi.edu), Michael Gebert (MGMax1919@aol.com), Bill Cruce (wlrc@uhura.neoucom.edu), Ed Weiland (emw107@psuvm.psu.edu), Bob Morris (morris@sce.carleton.ca) and many more who contributed a substantial amount of material and input to this FAQ.
In addition, I strongly recommend you read Henrik Herrannen's article, "How Film Is Transferred to Video", which is available via his WWW page at http://www.iki.fi/leopold/AV/FilmToVideo/.
First published October 1, 1995, last changed August 20, 2007.
Compiled by Henrik Herranen and Timm Doolen Compilation copyright 1995-98 Henrik Herranen (1994 Timm Doolen). All Rights Reserved Authors of individual contributions retain the respective copyrights of the original works they are excerpted from. This is essentially the FAQ produced by Leopold, but he has ceased publication.
LD stands for LaserDisc, the industry-wide term for consumer laser video. During its life, the format has also been known as LV (LaserVision) and CDV (Compact Disc Video). The players are also sometimes referred to as VDPs (Video Disc Players) and Sony calls them MDPs.
LD was first demonstrated by Philips and MCA in 1972, and has been on the market since 1978, or about as long as VCR and six years longer than CD. There are more than 1 million players in home use in the U.S. (compared to 85 million VCRs), and more than 4 million in Japan (10 percent of households there). The U.S. installed base is increasing at more than 15,000 units per month.
LD advantages
As with CD, and unlike tape formats, LD is a non-contact medium during play. There should be no wear in normal use, even if you freeze a single frame on screen for hours.
The theoretical shelf life of an LD that is "properly manufactured" and properly stored is the same as for CD -- essentially unknown, and possibly longer than the photographic negatives/prints from which the disc was made. There are no known deterioration modes for properly made and stored discs.
Contrast this with an optimistic shelf-life of 20 years for magnetic tapes of all kinds (less if used often). Tapes have several known deterioration modes: print-thru, binder breakdown, base stretch, and physical abrasion wear and signal loss due to external fields (magnetized VCR components, speaker magnets, CRT deflection coils, etc.)
Note the emphasis on "properly made disc" above. I have separate articles available on LD quality (LD#04), identifying LD defects (LD#17) and the interpretation of LD mint marks (i.e. who cast or pressed it, LD#09).
Discs do fail on the shelf, and experience other manufacturing defects more immediately evident. I have had several discs with "laser rot". I have also purchased discs with contaminants under the acrylic.
The initial defect rate for LDs is lower than for pre-recorded VCR tapes. The rate seems to be slightly higher for LDs (about 2%) than for CDs (which are about 1%).
The pulse-FM data structure on an LD (unlike ordinary VHS/Beta), is defined to hold all the information present in the composite video signal. Depending on source material and the transfer to disc, LD is above live TV broadcast quality: For NTSC, this is 425 TVL (luminance lines horizontally for 3/4 of the screen width) and about 482 scan lines, compared to 330x482 for broadcast. For PAL, the numbers are 450x560 and 400x560, respectively.
Compare this to 240x482 for good VHS (recorded, pre-recorded is probably less). Only recently have Super-VHS approached LD capability, and ED-Beta has gone even further with its resolution of 525x482. Of course, pre-recorded material is not widely available in these VCR formats. Even using S-VHS/ED-Beta to tape off-air still only reaches the 330x482 of the broadcast signal (400x560 in PAL countries).
Compared to LD, all consumer tape formats also fall short in time-base stability, chroma resolution, video noise and audio fidelity.
Although the video signal-to-noise ratio (s/n) appears to be about the same for LD and VCR hardware, it is probably not the same for mass-produced pre-recorded material. The LD process (casting or stamping) does not degrade the signal from master to copy. The tape process, magnetic contact printing, does.
All LD players have time-base-correction; mechanical, optical, analog electronic or digital. TBC eliminates the horizontal line jitter and color errors common on tape.
All sound combinations are not possible. The possible combinations are:
NTSC discs:
Most newer discs have a noise reduction called CX on the analog audio channels. CX noise reduction can be turned on and off anytime on a disc by the player (controlled by the disc itself). On Dolby Digital discs, or on discs that have separate contents for the left and right analog channel, CX can't be used (without problems).
The audio might be considered subjectively little worse than VHS Hi-Fi.
On NTSC discs, analog audio channels are nowadays often used to carry extra information, like commentary soundtracks. This can't be done with PAL discs, where analog and uncompressed digital channels are mutually exclusive. With NTSC discs, the right analog sound channel can be sacrificed to give the consumer Dolby Digital.
The last players with analog-only sound were made in 1989.
The uncompressed digital channels are the main audio reproduction system of today. Along with a Dolby Surround Pro-Logic decoder you may get a 4-channel output with 3 channels (front left, front center, front right) of full bandwidth (5-20,000 Hz) and 1 channel (back) with limited bandwidth (100-7000 Hz). Although only a limited amount of panning is allowed and some effects can't be done at all, the beauty in Pro-Logic lies into its ability to encode 4-channel sound on any stereo media.
PAL LDs can only have either analog or uncompressed digital audio.
Uncompressed digital audio has been used for 10 years now, and all new LDs have been with digital sound for years now. The last NTSC LDs without digital sound were done in the late 80's.
DD replaces the right analog audio channel of NTSC LDs with a 384 kbit/s data stream that can be decoded to 5+1 channels of sound. This system is sometimes called a 5.1 channel sound system, which means that 5 channels (front left, front center, front right, back right, back left) are of full bandwidth (5-20,000 Hz), while the 6th channel is a special subwoofer channel (2-120 Hz) that will be used only when the movie maker want to have heavy bass.
The DD track is heavily compressed: while an uncompressed digital channel use some 700 kbits/s, a DD full bandwidth channel can only use some 75 kbits/s (average). However, because perceptual coding is used and most of the time almost all of the sound energy is transmitted to the center channel, the actual compression ratio is most of the time nearer 3:1 than the presented 10:1 ratio. During my early tests (Crimson Tide, Star Trek Generations, Die Hard), I have been less than 10 times able to hear any artifacts that could be caused by compression.
With DD discs and non-DD LD players, you will hear static noise in the right analog channel. If your player is an old analog-only player, you have to switch to the left channel and listen to the film in mono sound.
DD is totally different from anything previously available at the home video market. It is a major breakthrough in home theatre audio reproduction, and to my opinion the jump from plain stereo to Dolby Surround Pro-Logic is smaller than the jump from Pro-Logic to DD.
DD is not available on PAL discs.
DTS is not an official part of the LD standard, but DTS discs can still be played with any NTSC laserdisc player.
DTS occupies the space reserved for digital audio on normal LDs, using a data bitrate of approximately 1.4 Mbits/s. In practise this means that those people who buy DTS discs but don't own DTS decoders, will only be able to listen to the analog soundtrack.
To listen to a DTS disc, one needs a laserdisc player with a PCM digital output, a DTS decoder, and, of course, enough amplifier power and speakers to carry the 5.1 channels.
I had recently (Aug-97) a chance to compare The Long Kiss Goodnight in both its Dolby Digital and DTS incarnations on a fully THX home audio system that costs more than US$20000 here in Finland. We also had a 100 Hz IDTV set, which doesn't emit the annoying 15 kHz squeal that all conventional TV sets do. Even if I tried, I was completely unable to tell any difference between the Dolby Digital and DTS versions. Right after that experience I bought my DD only decoder.
Nevertheless, some other people claim they can hear a small, but definitive difference in A/B tests.
Even if the situation has been improving during the autumn 1997, there still are not yet very many DTS titles.
Unlike tape formats, laserdisc is not a linear format. Like CD, you can go to the exact position on the disc you want. On CLV, you can position the disc to the nearest second. On CAV, you can seek to the frame number.
Most discs also have chapter marks, similar to tracks on a CD. Seeking frames/chapters is extremely quick on CAV discs because the speed of the disc does not have to change. Seeking time/chapters on CLV discs depends on the distance between the starting and end points, but never takes more than four to six seconds. Definitely faster than any rewind or fast forward on a VCR.
All players and discs can pause and search forward and back. Unlike VCR, there is no media or player wear when this is done.
CAV discs can also play forward and backward at variable speeds, from 1/90 normal speed to 10 times normal speed. Single-frame-step forward and backward is also available. Some newer players have a "jog wheel" that allows variable speed slow/fast motion. On most good pressings, the still-frame has the same resolution as the moving image, unlike VCR which often has blurring. A CAV LD can store 54,000 individual still images per side. The more expensive players can also freeze-field on CLV discs.
Yes. All current all LD players except a few high-end units can play 5-inch audio CDs. They are not usually as high quality as comparably priced CD players and often do not have as many high-end features, but they are not bad CD players. Some players have separate drives to spin audio-only CDs.
No. Nor with CDs and LPs. Even if an economical recording LD machine is ever introduced, it is too late for LDs to dominate the video market the way that VCRs have. In audio, if you want quality playback, you get a CD or LP player. If you want to record, get a cassette or DAT deck.
The typical LD owner is likely to have both a VCR and an LD. Lack of recording is really a non-issue as the LD product is currently positioned.
New LD players run from $300 (discounted) to $3,500. You can get a VCR for under $200. If you are concerned about features, the prices of comparable LDs and VCRs are about the same.
You can get a used player from $100 up. The only significant missing feature on pre-1987 players is digital sound. The video performance appears to equal Pioneer's current low-end machine (CLD-S201). Conventional wisdom in the LD world says to avoid players prior to the VP-1000 (circa 1981).
Having once bought a used VCR, I would not do that again (worn out head). An LD player seems less prone to wear, and even if it doesn't work properly, at least it won't eat your media (as long as you remember to remove that pesky shipping screw :-).
Unless you live in a major market (and in North America), you may have trouble finding a rental outlet. There are reportedly some 5,000 LD stores in the U.S., including a few chains, and over a dozen national mail-order sources.
If you are renting for auditioning of the program material, rather than for routine viewing, this is not a big deal. Rent tapes and buy discs. Or simply borrow discs.
Although the list of titles available on LD grows every day, several popular titles have never been in print or were available years ago, but are no longer in print (e.g. several of the Disney animated movies, which are usually not available on VHS either). The lack of software is usually cited by laserdisc opponents as one of the reasons to not get into LD. But the list of titles is very rich, and with more consumers and consumer pressure, more titles will be released on LD. What's amazing is how many titles there are to choose from considering the limited number of consumers. Personally, unless I win the lottery, I'll never be able to purchase all the titles I want to own, because the labels are producing them faster than I can buy them. So I usually don't worry about hard-to-find titles, because I know sooner or later the labels will release it if they can make some money off of it. In the meantime, my want list of released titles constantly outgrows my ability to purchase those titles. However, there is some sort of cosmic law (you might call it a corollary to Murphy's Law) that no matter when you start collecting LDs, at least one of your top five favorite movies will either be out-of-print or never released.
There's also imports....
In some cases, if a title is not available in domestic release, you may be able to find it as an import. Japanese LDs may have modified contents. Japanese moviegoers are more critical than Americans, and insist on original-language presentation, rather than dubbing. So unless the disc is widescreen, the Kanji subtitles may appear on-screen and in-picture.
An accurate Japanese LD catalog is required to know for sure. Refer to LD#02 for more information on imported LDs.
Also, Japanese films censor some types of nudity acceptable in U.S. [R] rated films. "THX-1138", George Lucas' first film, available on disc only in Japan until 1992, has flesh-colored airbushing. There are no uncensored [X] or [NC-17] American films at all in Japan. However, there's a huge market over there for X-rated anime.
CLV discs can store 60 minutes per side (64 for PAL discs), CAV allows 30 minutes per side (36 for PAL), requiring a side change at the end of each side. This is more of annoyance to some than others, and is a definite reminder that you are not watching a movie in the theater. The CAV version of Ben Hur requires 7 disc changes. Disc changes take at least several seconds, because the disc has to come to a complete stop and then start spinning again (whether you flip it by hand or have a multi-side player), each process taking at least two to three seconds.
In recent years, two-side players have become more and more affordable, allowing you to watch up to two hours uninterrupted on CLV discs, which covers a large percentage of movies.
For a detailed look at aspect ratios, look in section 14 of this FAQ. What follows is a nutshell explanation of letterboxing and aspect ratios.
The original aspect ratio of films from the beginning of the century to the early 1950s was approx 4:3 or 1.37:1. When television came along in the '40s it modeled its ratio after this number. When television started becoming popular, the film industry responded by introducing wider and wider pictures to the audience through various means, including wider film gauges such as 70MM, multiple projectors (as with Cinerama), and most commonly today, anamorphic projection, which uses special lenses to squeeze a wider image onto 35MM film. Aspect ratios for movies in the 50's and early 60's ranged from 1.37:1 all the way out to 2.8:1 for Cinerama.
By the mid to late '60s, most of the thunder of widescreen was over and many in the industry went back to shooting movies on flat 35mm film (non-anamorphic) and matting the upper and lower portions of the image to give about a 1.85:1 image.
When these films were transferred to another format to be shown on TV, you had to do one of three things: lose part of the image to cropping, letterbox the image so it would fit inside the tube or squeeze the image horizontally by not using the anamorphic lens during playback.
Of course in the '50s and '60s they didn't have 27", 35" and 50" TV screens with top-notch resolution and color separation, so letterboxing was not an option. Neither was cropping, because a 2.35:1 image is almost twice as wide as a 1.33:1 and much important action would be lost if you just cropped the sides off a 2.35:1 image. So they either squeezed the image, which causes the actors and objects to look very thin, or they gave it a pan & scan (P&S) transfer -- or both, in some extreme cases (often title credits will be squeezed, while the movie will be P&S'd).
For P&S, a telecine operator watches the movie as it is being transferred, and follows the part of the frame (s)he thinks is important by panning, thus the term pan and scan. Some P&S transfers of widescreen movies are OK, others are horrible. Occasionally if two characters are on opposite sides of the frame, you either see one or the other, or both of their noses in a P&S transfer.
Of course problems with P&S are: it throws the image composition off, it still excludes important information in most scenes (such as entire characters that are important to the shot), and it produces motion artifacts if people are moving in the frame during a pan. And not least of all, it adds a whole style of "camera" movement on top of whatever the director had already done (or not done), sometimes significantly altering the feel of a film.
So in the 1980s when laserdisc started becoming a popular format, consumers started demanding films be shown in their original aspect ratio of 2.35:1, 1.85:1 or whatever. The Voyager/Criterion company was instrumental in starting the letterbox trend - introducing letterboxing with their release of Lawrence of Arabia, and letterboxing all subsequently released movies that had non-Academy aspect ratios. (Woody Allen also insisted on a letterboxed presentation of his film Manhattan on cable and VHS around the same time.)
A laserdisc letterbox movie should always look better than a VHS letterbox movie because it has more lines of resolution to devote to the image. But there is nothing about the medium itself that prevents VHS movies from being letterboxed (in Europe, letterboxed PAL releases are very common). But the average consumer who owns a VCR and a 19" TV usually wants the full screen filled. To many consumers the "black bars" at the top and bottom of the image, which are a natural result of letterboxing, detract from their movie-viewing pleasure.
To the movie lover and video enthusiast, it is a choice they will have to make for themselves. But to be objective, it is best to view movies of several different aspect ratios in both letterbox and pan-and-scan format.
Of course, in many cases the bigger and more expensive TV sets are of better quality, which will make the difference show up better. However, with a good 25" set and a 5-6 ft viewing distance (my current setup, with a ratio of approx. 0.38), the difference between LD and VHS is huge. And when I get the money and buy the Philips 32PW9781 16:9 receiver, which has a picture width equal to a normal 35" TV receiver, I get that ratio up to 0.52 with widescreen films (and to 0.40 on 4:3 material, but that's not so important to me).
You really only need a huge TV set or a projection system if you wish to show your movies for many of your friends at a time or you have another good reason to have a greater viewing distance.
Discs cost about twice as much to manufacture as tapes, but new release discs often sell for less than new release tapes.
VHS tapes are the dominant home video medium. Most people rent tapes rather than buy them. The film studios don't get a percentage of the rental revenue, just the income from the initial sale of each prerecorded tape. Video stores are in hot competition to get new titles fast, so it is somewhat a "captive market." The first tape sales are therefore targetted at, and priced for, video rental stores - not for collectors.
Consequently, new tape releases are priced very high ($80-$90 is common). It is not until the the video store demand is satisfied that studios drop prices to levels attractive to individual movie collectors ($30-40). When that market is satisfied, prices may drop further for the mass market customers, $10-20 per tape.
In contrast, LD has been a "sell through" market. The major purchasers of new LD releases are individual movie collectors. LD rentals are not a big market, and there is no low-end mass-market at all. LDs, even major titles like "Top Gun", are typically introduced at $30-40 (for CLV), and stay there. Many recent titles have come in at well below $30. Incidentally, routine 10% discounts are common for LD. I have a separate article, LD#14, available on LD mail order sources.
The exception to the generally low prices in the LD market is the Criterion Collection. Criterion releases run from $40-70 (CLV) and $60-125 (CAV). They are worth it because they seek out the finest possible source material (archival negatives, etc.) and deliver the most complete product, often with generous motion, still-frame and multi-channel audio supplements.
LD producers sometimes announce titles before they have the rights completely nailed down. This may be carelessness, but there are other causes as well, such as "surprise" old contracts that turn up late, and contain language that failed to anticipate LD (e.g. "We hereby assign to OneTimeVideo the LP, cassette and video tape rights to 'Revenge of the Valley Girls III'. All other rights are retained." So who has the LD rights?
LD producers also often announce titles after clear rights have been obtained, but before acceptable mastering source elements have been located. MGM/UA says the entire old United Artist vault materials are in sad shape. Criterion often announces it will offer a title when it gets the rights, long before they have collected, collated, annotated and transfered all the CAV supplements they are so famous for.
The practice of pre-announcing has the advantage that the major dealers often offer 15% pre-release pre-order discounts, sometimes as high as 25% on megatitles. The dealers get a larger discount on large initial stocking orders, and they can pass it on.
Once rights and source material have been obtained, the LD producer must schedule transfer time and pressing time, further complicated if closed- captioning or other special-processing is used. LD jacket artwork and editiorial content needs to be prepared as well. There are a limited number of video houses who perform quality, LD-compatible telecine transfers; fewer yet who offer digital transfers. There are only eight pressing plants worldwide that are routinely available for NTSC LDs. If they all are flooded with "megatitles", lower volume titles get delayed.
Pressing plant capacity also affects inventories of back-titles. New issues often sell-out, and are not re-pressed for six months or more. If you are just starting out in LD, expect some frustration in finding all the back titles you seek.
There are at least six separate entities involved in getting visual works from the film/tape vault onto acrylic plastic and delivered to your hands:
Ignoring Public Domain for the purposes of this discussion, the studio holds the copyright on the work in question, and usually custody of the archival film or tape elements. The studio may not actually initiate the LD release. Until recently, with a few exceptions (MGM in particular), the LD release was actually championed by the distributor. The studio merely grants permission and provides a key to the vault, so to speak.
The label hosts the release, lists it in their catalog, and may hold the home video rights as well. The label may also be a studio and is often a generalized entertainment conglomerate. There are well over 100 "labels" on LD in the U.S.
Converts the master videotape into a "glass master" for each side of the disc. Normally, glass masters never leave the manufacturer's control, but there have been reports of mixed mint marks, implying that one vendor made the masters, and another made the stampers and media. Glass masters are used to make one or more metal stampers that press or cast the actual disc media.
The manufacturer presses (or casts, or injection molds) the media. They may also manufacture the disc labels, sleeves, jackets, and/or assemble the end product. With the exception of Pioneer, and some early 3M titles, manufacturers seldom act as "labels" or "distributors".
There are only six significant LD manufacturers in the continental U.S. There are at least five off-shore manufacturers that matter here, and perhaps more making discs in Japan for local consumption there. The significant sources are, in order of probability of encountering them:
The distributor warehouses the finished product, and ships it to retailers. A distributor usually publishes a catalog. A distributor may have exclusive access to certain titles, labels and studios. Some labels (e.g. Warner, MCA, Voyager and Lumivision) handle their own distribution (although non-exclusively). With the exception of Voyager Press, distributors generally don't sell directly to consumers under their own name.
There are only 2 broad-line LD distributors that really matter in the U.S.;
The retailer sells directly to the public. Retailers may source from multiple distributors, so they theoretically can get you anything that is in print (or in a warehouse somewhere). The larger chains may handle their own distribution.
There are three major types of consumer laser video media:
There are some 8-inch LDs that are made exactly the way CD's are - complete with the painted labeled on the non-playing side. LDs that will play CDs have no problems with these. Older players need a 'shim' disk, which is placed over the real disk in the player. This give enough thickness of the clamping mechanism to work. Otherwise these are not playable in older machines. The advantage of these are that they can be produced exactly as a CD can. However, these discs are rare.
The 5-inch (CDV5 or just CDV) is single-sided, and can contain about six minutes of full-motion video/audio plus 20 minutes of audio-only. As with CD, CDV5 is polycarbonate on the data side, and lacquer on the label side. Any LD player that can handle CDV5 can also handle audio-only CD. CDV is all but defunct in the United States but still popular in Japan.
At present, no LD combi players can handle the new CD-I full motion video and VideoCD formats. Since the basic quality and nasty artifacts of these highly compressed formats render them less pleasant to watch than VHS, they aren't likely to be of interest to anyone seeking laser quality home theatre.
CD-I and VideoCD don't appear to be much of a threat to LD. Anyone interested in LD is apt to be in the market because they are weary of the limitations of VHS. One look at 5-inch compressed digital video will make it clear that CD-I and VideoCD are no alternative to LD, and aren't even a net improvement over VHS for home theatre purposes.
Other buzzwords: LD players (whether combi or not) do NOT presently support CD-ROM, or CD-ROM/XA (audiofiles), DVI, CD-I (interactive multi-media) and VideoCD formats. Until recently, only Karaoke LD players supported CD+G subcode text. Pioneer has "LaserActive" players which support CD+G, LD-G, Sega CD-ROM games, Genesis 16-bit game cartridges, and a new format: "MegaLD" 8- and 12-inch LD-ROM2 discs.
NTSC stands for National Television Systems Committee, and is the TV system used in North-America and Japan. It has 60 fields (30 frames) / second, 525 horizontal scanlines (480 visible), and a 3.58 MHz colour carrier wave. Only LDs made for the North American and Japanese market are NTSC.
As with VCRs, the only significant "grey market" media sources for North American customers are Japan and Hong Kong. Encoding is really a non-issue for NTSC consumers, and U.S.domestic discs are sometimes not even labelled "NTSC".
There is a problem with movement when transferring a film to NTSC: 30 frames/s, or 60 fiels/s of NTSC is not divisable with the 24 frames/s used in almost all films. The problem is solved in the following fashion: Two consecutive film frames lasting 1/12 s are taken. The first film frame is shown for 2 NTSC fields (2/60 s). The second film frame is shown for 3 NTSC fields (3/60 s). This makes a total of 5/60 s for NTSC video, which also makes the 1/12 s the original film frames were supposed to last. This system is called 3/2 pull-down.
There are drawbacks in this pull-down system: to some viewers (me included), slow panning looks much more jerky in NTSC compared to the original film experience, or PAL, which typically uses 2/2 pull-down.
Because films have 24 frames/s and PAL has 25 frames/s, it is most convenient to show movies at the frame rate of PAL. This makes movies last 4% less time and makes all voices little higher. Usually this makes little difference, but for me watching Pink Floyd's The Wall in PAL is almost like torture.
CX noise reduction is the rough LD equivalent of Dolby-B for audio tapes. CX is only used on the LD analog channels. There has been a lot of debate about CX. Criterion, for example, only uses CX when the original audio source material has wide dynamic range (i.e. frequently not on early optical soundtracks mastered on film). They do not use it where the programs on the two channels are different, as it can cause decoder mistracking.
Rotation modes: LDs can be mastered for either constant linear velocity (CLV, variable rpm), like a CD, or constant angular velocity (CAV, constant rpm), like an LP. All consumer players can handle either format. Some releases even mix the modes, with the initial sides being CLV and the final side being CAV. Some films are initially released in both CLV and CAV "collectors" editions.
CAV is also known as "standard play" or "full feature play". Only CAV provides all motion control capabilities on all players (at the expense of more platters and shorter 30 minute sides). CAV also provides constantly improving signal-to-noise ratio as the program proceeds toward the outer edge, but this is typically not that noticeable on properly manufactured discs.
CLV is also known as "extended play". One hour per side playing time results in lower prices and less flipping. In return, you give up all the other CAV features, unless you have a high-end player with digital field store.
The majority of disc titles are available only in CLV.
A Comparison Between CLV and CAV discs on different players (NTSC discs):
Ordinary Digital
Player Player*
Disc format CAV CLV CLV
Rotation velocity (rpm) 1800 1800..600 1800..600
Maximum time per side (minutes) 30 60 60
Simple fast forward/reverse Yes Yes Yes
Variable fast forward/reverse Yes No Yes
Variable slow forward/reverse Yes No Yes
Pause (with blank display) Yes Yes Yes
Still frame (field on digital CLV) Yes No Yes
Still step Frame No Yes #
Seek to chapter Yes Yes Yes
Seek to time No @ Yes Yes
Seek to frame number Yes No No
* - Digital field-store CLV is a feature of the player, not the media.
@ - Current time is stored in the vertical interval on CLV discs. That structure is used for frame number on CAV discs. However, the P-Q subcode fields, also called TOC for Table of Contents, of the digital audio track can contain elapsed / remaining track / side time on CAV discs.
# - CLV still step on consumer players is either one revolution (typ on Pioneer), which may be several fields, or may be one frame (typ on Sony and Panasonic).
To be exact, the discs that nowadays are entitled CLV, are actually CAA discs. In CAA the disc speed is not slowed down constantly, but it is kept constant for some time and then rapidly slowed down. The point in this system is to keep the horizontal sync signals aligned on adjacent disc tracks to keep crosstalk to a minimum. In Blaine Youngs (blam1@oz.net) words:
"CLV: This format is dead. The name is still used for simplicity's sake, but 3M is the only manufacturer which uses it. In 1982/3, there was a shift to CAA. This is the only format used today. (Again, except for 3M which incorporates a minor variant on CLV to eliminate crosstalk). Regardless of which format is used (CLV or CAA) it is still required to have crosstalk rejection code built into the mastering software to prevent master crosstalk. Technidisc does not use such software and as a result, most of their CLV stuff looks like crap.
CAA also offers something else, 5 different encoding routines. This will allow for variable playback times, depending on the program. What happens is that the initial CAV pattern at the beginning of the disc is altered (lengthened or shortened as necessary) and the track pitch is modified. The 5 formats are CAA45, CAA55, CAA60, CAA65 and CAA70. CAA45 has been used only once, that I know of. Any disc side running less than 55:05 uses CAA55 encoding. All other discs are CAA60. There are 2 known occurances of CAA65 and there has never been a CAA70 disc released in the US."
From now on, CLV and CAA discs are just called CLV for simplicity, and because that's what's written on the disc sleeves.
While technical differences between CAV and CLV are discussed below, it should be noted that the choice of format is only one factor, and not necessarily the most important one by any means, in determining the eventual quality of a disc. The care taken during the mastering process and the condition of the source materials are of at least as much importance. With the improvements in mastering capabilities over the years, it is not unknown for a CLV disc released today to look and sound better than a CAV disc mastered several years ago (e.g., the new Criterion transfer of Citizen Kane compared with the one that was released in the mid-80's as the very first Criterion Collection disc). In short, the technical differences between CAV and CLV are discernable only at the ultimate point of the respective formats' capabilities. The best CAV disc will look and sound better than the best CLV disc, but a good CLV disc will look much better than an average CAV disc-- while even the best VHS tape won't compare with any competently made disc.
Leopold continues with a table comparing CAV to CLV:
For free-run playback, not really. There is a quality difference between CAV and CLV, but it is small, and way less dramatic than say, S-VHS vs VHS.
Of course, for seek/still/step/slow/fast, CAV is at least twice the image quality of CLV, and on most players, offers functions that CLV discs can't duplicate.
A branded "Dolby Surround" decoder
In any case, a maximum of 3 dB of separation is achieved between each adjacent pair of: left-center-right-surround-left.
THX is not another encoding scheme. It's just a quality assurance system that tries to take the most of Dolby Pro-Logic. (Don't confuse this with THX certified discs, we are talking about audio decoding hardware now.) A THX-certified processor starts with Dolby Pro-Logic and adds
The advantage is this: in a normal 2.35:1 NTSC transfer you get approx. 273 active video lines (482*(4/3)/2.35), but with a 16:9 release, you get approx. 365 lines (482*(16/9)/2.35). This will reduce line flicker and greatly enhance vertical resolution compared to a non-anamorphic representation.
The same numbers for a 1.85:1 film are 347 and 463 lines. And this is really interesting: with this film format the 16:9 version has to leave only 19 NTSC video lines unused. Thus, you get the full resolution of NTSC in a widescreen release!
Naturally, to make an anamorphic version of any picture material that is less wide than 16:9 (1.78:1) would be counterproductive, because then you would have to leave black bars on the left and right side of the screen and begin to lose horizontal resolution that way.
So far only few LD titles have been released in 16:9. As I'm writing this (97-08-13), some titles have been published but none are available at the moment in USA.
Qualitywise VHS is worse in every aspect: Less luminance resolution, less colour resolution, more picture noise, no digital sound, tracking problems, plus normal tape wear and tear. But, Joe/Jane Average doesn't care of the picture is bad. He/she doesn't even care if 40% of the original area of the picture is lost in a panned and scanned (P&S) version of his/her favourite movie.
S-VHS is much better, but there is no program material available for it. Enough said.
When the images are not moving, CD-I appears to have a steady and non-noisy look. But when the picture has much movement, the very low picture data rate of 1.1 Mbits/s makes the picture break into little 8x8 and 16x16 pixel MPEG-1 -compression blocks, which makes any action film look totally disgusting. When you are supposed to be lost in high action, you are lost in compression blocks.
CD-I discs are claimed to be both NTSC and PAL compatible. This is carried out with an evil scheme: the discs are mastered in a way that makes everything appear 10% too flat on PAL TVs and 10% too tall on NTSC TVs. I find this way of solving problems to be totally unacceptable.
The video compression ratio on CD-I is approx. 40:1 and audio compression ratio is approx. 5:1.
Many current DVDs have two versions of the movie on opposite sides of the disc: on the other side a 4:3 open matte or pan & scan version, on the other side a widescreen version, which often is a 16:9 enhanced, or anamorphic transfer. If the user doesn't have a 16:9 compatible TV set, DVD players can be asked to downconvert the anamorphic version to a regular 4:3 letterboxed version, with some loss of picture quality.
At this moment there are still not that many DVD titles. But if the format survives, this will probably change in a year or two.
Now, let me make this one thing absolutely crystal clear to all who haven't had the chance to see DVD in a proper environment: DVD does have better picture quality than LD. Period. There is no need to argue over this. Here are some reasons:
But what if you have seen a DVD player in a store near you and you thought the picture sucked big time compared to the LD home setup of yours? Here are some reasons that might be (and probably are) set incorrectly.
For more information, have a look at the DVD Frequently Asked Questions at http://www.dvddemystified.com/dvdfaq.html.