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DVD - introduction
Jan 1, 1995 - by Franck ERNOULD
We've heard enough of this : say goodbye to CD's, CD-ROM's, VCR and others, it's DVD time ! The good points of this new support are as well obvious as conclusive. However, one whispers that some producers won't be able to deliver their players on time (Christmas 96 in the U.S., mid-97 in Europe). Explanations...
Let's start first to clarify things : DVD stands for Digital Versatile (not Video) Disc, which means universal numeric disc. As described on our comparative table, CD and DVD only have the size in common ! Originally, the first ones to ask for a new numeric support were films editors. Aim purchased : to replace, for the common people, the good old VHS (which celebrates its twenty years old existence, in the most discrete way, speaking in media terms), as pre-recorded tape.
Unfortunately, once numerised, a video signal appears to need lots of binary data. A compressed good quality pic, in MPEG-2 for instance, 720x480 pixels, 30 i/s - let's remind that VHS hardly achieves a 480x320 resolution -, with 3 versions of multicanal sounds 5+1, requires an average transfert level of 4,69 Mbits per sec (in fact, it oscillates, according to sequences complexity, between 3 and 8 Mbits per sec, which is shown on the opposite figure). It was thus impossible to work with an ordinary CD, format for which Philips assure that 600 million players have already been built (among them, 70 millions of CD-ROM players)...
| Anatomy of a upcoming standard | |
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DVD is read by a red laser ray, it turns faster, tracks - and basic basins they contain - are size less. Final result : the cd average capacity (700 Mo more or less) looks a little slight considering the 4,7 Go of a DVD side, which can contain a 133 minute movie, allocating a 3,5 Mbits/s binary flow to the image, and a 3x384 Kbits/s to the multichannels 5+1 (add the 32 sub tracks, used especially to insert sub-titles, and you get the 4,69 Mbits/s just mentionned).
Up till now, if everybody seems to agree upon this support as a video data provider, whose quality almost equals the professionnal Betacam's one, nothing can avoid an editor from engraving on a DVD a much detailled picture, possibly at a 16/9 format, or contrariwise, to put a stereo PCM linary sound in place of the 5+1 sound compressed AC-3, at the risk of a lower quality video.
Control is very large on that point, you just need to stay under the maximal debit of 10 Mbits/s. To speak about storage, admitting that you'd get short on capacity, you ought to know that the very same DVD side can hold 2 different data layers : the first one uses the same rules of making - therefore of reading - that CD's, while the second layer uses more sophisticated techniques, based on notably ultraviolet sensitive resins and partial reflection/transmission partielle materials.
Particularity : in regard of the high hole & bump miniaturization, it's physically impossible to press a DVD at once, because it would be impossible to get over the potential deformations while reading. Thus, this support is made by sticking two sides, like in an actual LaserDisk if you will, even if it has only one side "useful". Engraving both two sides, you can get 17 Go of maximum capacity, that's to say 25 CD's, on a whole 120 mm of diameter disc ! In the manner of the mini-CD, a 80 mm version, with 1,4 Go single layer capacity (2,6 double one) is planned for some applications, especially portables. At the moment, a DVD player transfert rate is height times faster than a simple speed CD (let's remember that this old standard is now pushed at 12 times speed on lastest machines), which let think of new horizons for video on upcoming DVD-ROM. Do I need to remind you that animated figures reproduction is at the time a huge problem for almost every actual multimedia titles available on CD-ROM?
| What for ? | |
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Every application area have already been surveyed, and specifications, gathered in DVD books, considering what's done for CD : DVD-ROM, DVD-Video, DVD-Audio, DVD-WO (Write Once) ou DVD-R, limited at 3,9 Go per side. A DVD-E (Erasable) is even scheduled… The different details concerning information division on tracks are established, the only obligation is to forsee at least one PCM stereo sound for movies (concerning multichannels formats, DTS and Dolby AC-3 are currently in competition…). DVD is meant to replace, in few years, videotapes, laserdiscs, cd-rom and audio cd's. Domestic video should be the first target (Time Warner was supposed to display 250 movies at launching, the driver was supposed to cost around $700), followed later by the personnal informatics, which uses games that requires more and more memory (a dvd-player, upgradable to a video-player by adding a MPEG2 card, should cost from $200 to $500). Selling approximations from different builders count dozens of millions DVD-player copies for Y2K…
And the audio applications are not left apart. There's no doubt that the support will allow a sound quality never reached before : 24 bits sampled at 96 KHz will soon become reality. Moreover, with ascending compatibility, DVD players will play standard audio cd's, displayed at more than ten billion copies worldwide since 1982, but unfortunately they won't play CD-R up until now, because of a wavelength problem. One even consider to build universal audio DVD double layer : one of them, completely compatible with actual CD players, would offer a signal in conformity with Red Book (44,1 kHz, 16 bits), and thus also readable by older players - that's what they call descending compatibility -, while the other one would bring incredible sound, without any concession. Do the math : a 4,7 Go side provides two and a quarter hour of 96 KHz music ! What would you do with such a capacity, considering that most audio cd's running time is far from the maximum authorised of 74 minutes ? The answer is up to editors who seem to like paradoxes, as we're about to find out...
| We stop everything ! | |
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The year 1995 was entirely stamped by the mercyless fight between the SD format, made by the Toshiba/Warner/Matsushita alliance, and the MMCD, conceived by the Philips/Sony duo.
Careful not make a ruinous remake of the VHS/Betamax war, or, closer to us, DCC/minidisc, the opponants agreed in December 95 on a common format, DVD, and all industries get on board : Microsoft, Intel and Motorola. The question is : why is the moment to start making benefits (international DVD market represents billion dollars !) postponed, while manufacturers seemed to achieve their goal, after long years spent for research ? This time, that reaction is based on movie producers, whose help is necessary - we talked about that - to launch the new support on the market. The time Warner Group is very influential in the DVD consortium, and so is Pioneer, world leader on the actual analogic LaserDiscs market. As majors did in 1987 for DAT, owners of hollywood films catalogs have suddenly find out that their precious films were going to be distributed among the large public audience, with image sound quality respectable, at least far better than the ones proposed by VHS. And what if the generous consumers-customers become dangerous crackers ? Maybe not with the unborn DVD-WO, but at least with new numeric video formats accessible to anyone, DV and others, which appeared recently ? What if unscrupulous individuals decided to copy at a numerical range, which means no visible degradation, from a commercial DVD ? And if you'd ruined launching stategies of a movie planned to be distributed differently from a country to another, allowing anybody to buy anywhere movies engraved on an universal support, so that French fans can read a american film totally unpublished in France ? That was enough to paralyze the system...
| A well complicated situation | |
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Thus, DVD video specifications have gone from version 0.9 to version 1.0, unveiled in mid-september in Brussels. Too bad for optimistic makers and editors who had already started their own production line, just to be sure to be ready for the official DVD lauchning, planned a long time ago for Christmas 96. Anything that have been engraved or assembled unitl now is illegal and unexploitable ! The SCMS Syndrom hits once again : from now on, binary flux engraved on DVD-video will integrate specific codes, whose interpretation will need up to 1/15 ressources of CPU integrated in the player. Without being too sophisticated, what would head off exportation, algorithm protection used will avert any unauthorised exploitation of the movie, and will doubtless be implanted on every published title, including older ones. On October 29, definitive version of this protection has been set. DVD-Rom won't probably use it, which explains that Pioneer has been ble to introduce such a player to SATIS for the first time. From now on, a disc pressed for a specific market - for instance, the US - won't be readable in Europe, where players will compare their own regional code to the one on the disc. A possible numeric copy would be detected the same way, and ruthlessly be jammed. Hackers are given here opportunity to enjoy, and so are parallel amrican players importators… Just a quick note : considering the fact that dubbing and subtitling operations are made at the last moment, just before the programmed release of the movie in the different foreign countries, and so often after its video edition in the US, what elements hollywood studios will they use to fill up their extra audio tracks and the numerous subtitling channels allowed by DVD?
| I will wait... | |
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Anyway, the first demonstration of a 80 minute audio DVD, with 24 bits 96 KHz sound and fixed images, scheduled by Pioneer-Japan in September, during a Hi-Fi exhibit in London, was delayed and replaced by the introduction of a real DVD. Some may say it wouldn't be useful to allow the customer to doubt, by presenting what might be taken for a new audio format. That would make the customer stand a waiting position, and so on that would reduce CD sales, still respectables… One also whispers that first DVD players would be provided with 20 bits only converters, and that they would not appear until 1997. At Apple Expo, during its presentation at the DDD stand, the DVD creator (video mastering and authoring solutions environment), it was from hard discs that image files and sounds corresponding to the upcoming DVD ones were read. the less we can say is that the situation is not really clear. In France, major video editors are already submerged by demo discs. The MPO firm get equiped in pressing, and the first french DVD is expected for mid-december. After hard long negociations, protection anti-illegal use which was evocated a few minutes ago will be manufactured at assembling, by a black box. say this in other words and you'll mean that editors have nothing to remove or modify from their elements already built up and ready for sale. Manufacturers are frenetically adapting their players to new rules, not to miss the schedulded launching date : Christmas 1996 in the U.S. The optimistic ones say that players are already available in Japan, and that it won't take long until they invade the rest of the world. Others, contrariwise, pretend that wasting time is close to six month, meaning that the system "true" first european steps wouldn't be made before the end of 1997. In parallel, experts established that recording supports are cycling each 25 years : the first disc was successful from 1935 to 1960, the LP from 1960 to 1985… Following this point, VHS and compact disc will give way to DVD long after Y2K ! Until that time, they'll still provide us long time of pleasure...
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DVD and C++
This is for the most curious of you : DVD players will be able to understand C++ ! Editors who will want to will be able to insert on the support routines written in that language, telling player what to do when the disc is inserted, or when user pushes the remote control : menu, signs up and down… That's an elegant way to surf through the different files engraved on the disc, which can allow different editions of the same movie (short or long edition, two different endings shot by director, or different versions, a la Blade Runner), to reduce access to some scenes specially not recommended to sensitive people, to surf through the different subtitles and sound versions, to choose the angle to look at the scene… This interactivity will doubtlessly remind of CD-I Philips, another "upcoming" standard fallen during the fight.
Let's talk about sound
Bits and frecency rates competition has been running for several years now… DVD will allow, at first place, to forget about the process that fixed on 16 bits a signal encoded on 20 or more, like (not to mention other ones) the Sony Super Bit Mapping. Sony solutions has already developed an complete 24 bits 96 kHz audio environment, whom Michel Jonasz used a prototype for the first tiime worldwide, to record his last album mix : "Soul Music Airlaines). His example is expected to be followed by other artists passionated by sound quality… Of course, it will be required to start the reports of every analogical records at that format before releasing them - lots of work upcoming for the mastering structures, and lots of benefits for majors !
Several unknown data remain : which prize will be proposed to people for such exceptionnal sound recordings ? How many music fans own the equipment to notice - and to hear - the difference with an ordinary CD ? Is it not a paradox to see the production of bits running phenomenon on the one side, and on the other side the diffusion to generalization of numeric compressions ? To pretend that DAB, compressed MPEG-2, multichannel sounds AC-3 or DTS or even stero sounds sent by cable or satellite in numeric format, provide quality strictly equivalent to CD is a lie… In brief, this is a wonderful bi-speed system that's to come!
Sonic Solutions DVD Creator
This environment allows at first place acquisition of different image and sound files. A Macintosh usually control many video cards set in a PCI rack, "audio" solutions already existing at Sonic. Once image and sound compressed, recorded on hard disks connected Medianet network, you enter Scenarist, "authoring" software running under Unix on station Silicon Graphics. Scenarist lets you assemble the different DVD components : audio and graphic files and "attachment", accessories. Where VHS or any other support using tapes could not offer, by nature, an easy access to the many sequences it contains, DVD lets you browse between things without waiting a second. Moreover, the user interface provided is much more elaborated than an audio CD's, for instance. We're half-way between CD-I and CD-ROM. When DVD is inserted in the player, it displays invariably a "homepage" built like a graphic document. As the "hypertexts" links, you just have to "click", with the arrows of the remote, on some zones or buttons to go through a path defined at advance during the "authoring". The number of programmable paths is very high, which will make the DVD an ideal interactive introducing tool, for example. This principle probably reminds of AppleMeida Tools, notably, so as "links" are displayed, at their programmation, as crow lines binding "blocks" symbolizing different files. Thus, the graphic interface as displayed to user is entirely settable. Once the "authoring" phase done, you have to "multiplex" all MPEG files, and then create an ISO image of the master. It gathers each data effectively used, stocked on hard disk or DLT tape. From that image is the simulation done, to check everything is in place (Scenarist emulates, in the window, the user's remote !). Silicon Graphics station then uses all ressources to decompress, by itself, in real time, image and sound data (displayed on a little window with stereo sound for the moment). If everything is correct, you now just have to send the DLT tape to the pressing factory !
A great thanks to DDD, and specially to Paul-henry Wagner, to have given us a high demonstration of DVD Creator possibilities - that helped us to understand advantages of this new support. Also a big 'thank you' for letting us used the different docs which illustrate this article.
translated by TheAmbassador
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