 The magazine of the Melbourne PC User Group A brief history of CDs - from DA to DVD Peter Stanski |
In 1980 Sony and Philips set the standard for the digital audio (DA) compact
disc format. In 1982, the first Sony CD player called the CD-101 was released with Billy Joel's 52nd
Street being the first musical production. With the success of CDs the first portable car players became
available in 1984. Then, in 1985, the automatic CD changer with a carousel appeared on the market. In the
1990s, the industry began to adopt various storage standards to unify the plethora of hybrid CD formats
perfected by third-party developers. These commonly agreed-upon formats were published in a set of
coloured-cover books, becoming commonly known by their de facto names as the coloured-book standards. Today
many formats are available for various applications such as computer data storage (CD-ROM), imaging
(PhotoCD), interactive multimedia (CDi), multi-session data and audio (mixed mode 1 & 2), with the most
common of these being the digital audio (DA) format.
New appearances
In the last two years some new technology has begun to make waves in the CD industry. The first was the
announcement of the CD-Erasable media in 1995. Erasable CDs were not marketed with a great deal of effort,
which has resulted in very few people knowing about the technology. Since 1995, erasable media has gradually
filtered into the consumer market allowing CD-Recorder (CD-R) units to re-use mastered CDs - rovided erasable
media was used. Prior to erasable media, developers and home users could not re-use badly recorded CDs. These
often ended up as office frisbees, coffee coasters and eventually in bins. With erasable media, the CD can be
re-used allowing new versions of data to be re-written onto the CD. The down side is their 1000 percent
higher price tag than conventional CD media. Despite this, erasable CDs have been hastily accepted by
in-house document publishers and multimedia developers.
DVD technology
In 1995, work on standardising the emerging Digital Versatile Disc (DVD) had begun. The final standard made
public in late 1996 has now settled the heated discussions on what the final format would look like. There
were talks of double-sided CDs and some speculation on single-sided double-density formats. Well the vote is
in, and the format as listed by Sony is a single-sided dual-layer disc. Despite this, there is still talk of
extending this to double-sided media by Hitachi.
This means that DVD reading mechanisms will still maintain backward compatibility with existing CD
technology. The new media format has the same dimensions both for diameter (120 mm) and thickness (1.2 mm).
However, the CD mechanisms boast faster transfer speeds (10 megabits/sec) and will carry variable speed
video, audio and sub-titles (see box for more specifications). Perhaps the greatest achievement by DVD
developers lies in the capacity to store entire feature films on one single CD. Those familiar with current
technology often find that they have to insert the second disc after the first hour. DVD manages to store
whole films and lets the viewers enjoy uninterrupted viewing. This had to be done by providing more storage
capacity on the media. The DVD format stores 12 times more data than a conventional CD. This allows for a
storage capacity of 4.7 GB for single-layer discs or a total of 8.5 GB for dual-layer discs.
DVD storage format
Since the size has not changed and capacity has increased, the developers had to find a way to pack more
information on the same amount of CD real estate. The way that information is encoded on a CD is through
small pits located along a data track. You can think of it as a road with pot holes in it. The holes indicate
1s and 0s, which make up the basic building blocks of data. In the case of DVD, information is encoded within
the tracks, which have been increased in number per layer. This translates to having a footpath instead of a
road, on which you encode your data. Since roads are wider than footpaths, by having more footpaths (tracks)
than roads, you effectively increase the storage capacity of the media without increasing the size.
Smaller inter-track spacing requires much finer Numerical Aperture (NA) lens to read the smaller pits, and a
much finer laser focus control. Conventional CD-ROM drives use a laser that emits infrared light at
wavelength of 780 nanometers (nm), while DVD uses red light at 650 to 635 nm. Shorter wavelengths allow for a
narrower laser beam to reflect off the pits within tightly spaced tracks. These improvements in CD encoding
and laser optics have made DVD a reality.
Digital video and audio
To provide full-frame video at 167 megabits per second, the DVD would only store about four minutes on a
single-layer CD. Therefore, this implies that some sort of video compression is required to store an entire
film. The MPEG2 video/audio compression standard has been around for a number of years. Standardised by the
Motion Picture Expert Group (MPEG) it is used to encode films on DVDs.
On a single-layer DVD over two hours can be stored (approx. 133 min). On average, 4.9 megabits are required
for one second of video and audio. The standard allows for 5.1-channel digital (Dolby AC-3) sound in three
languages with additional sub-titles in four languages. The Dolby AC-3 channels are discrete individual audio
channels dedicated for each speaker (front left and right, rear left and right, centre and 0.1 for the
sub-woofer). Home theatre enthusiasts will especially be pleased to have AC-3 for true cinema-like surround
sound. Additionally, for international movie distribution, by falling back to 16-bit linear Dolby Pro Logic
encoding (still CD quality), producers have the capability to encode up to eight language audio tracks with
32 sets of sub-titles. This makes DVD a truly digital and international movie format.
Additional extensions to DVD films include user selectable camera views along with a viewer rating system.
The possibility for viewing the one film from several camera angles opens up a whole new dimension in
entertainment. Viewers will be able to change between several available angles and have the facility for zoom
in and out of screen regions. With super-still and flicker-free pausing, these facilities will bring
production quality entertainment to the home user.
The parent lock option for setting viewer rating means that children can view a modified version of an adult
film. This feature will set the playback of selected titles into child or adult modes complying with the PG,
AO and R classifications. It is important to realise that some of these features may not be available on all
films, as they need to be specially encoded. Also, features such as zooming and scrolling, or displaying of
picture-in-picture (PIP), are specific to the brand and quality of the DVD player.
DVD-ROM
Besides storing full length feature films, DVD technology may be used to store computer data. This would be
ideal for multimedia presentations and games that are already appearing on multiple CDs. Those wishing to
archive onto DVD-ROMs may have to wait for some time as Hitachi and Toshiba seem to be the only
manufacturers. Also to add to the terminology, the name given to DVD-ROM re-writable is DVD-RAM.
The final procedure on burning your own DVD-RAMs seems a little shaky right now. This is to do with how
exactly the CD-Writer should record the information onto a DVD disc. The DVD-RAM recording process as
proposed by Panasonic and Toshiba, involves recording by landing and grooving on the media and encoding a
double spiral. This technique is said to be space-efficient but may be error prone due to variations of beam
accuracy. On the other hand, Sony and Philips suggest that burning should be done along a special guide
groove which is more reliable but less efficient.
With re-writable DVD-RAM technology, it may be possible to replace your home VCR with a DVD recorder. This
means that video tapes which start losing quality while sitting on your bookshelf for a few years could be
replaced with DVD-RAM discs. This would significantly increase the life span of your favorite films. Digital
video may seem like a radical jump for most domestic users because completely new hardware needs to be
purchased. The down side is that this technology may not be available before the year 2000.
From DVD to Divx
With the advent of DVD, Paramount, Universal, Disney and DreamWorks are going to provide DVD feature films
at the cost of $5 per disc. Wait for it, there is a catch. After you buy the disc you will be able to watch
it for 48 hours. After that time, your DVD player will not play the disc unless you unlock it by paying for
another viewing of it. How exactly will you do that?
The DVD player you use has to be a Divx (Digital Video Express) compliant DVD player. Normal DVD players will
not be able to play those titles as they will not be the same format. Divx players will have a built-in modem
that will dial up the Divx server and charge your credit card. This slowly begins to look like a
sophisticated video library. No-one is sure if this is likely to take off, as people with DVD players face an
abrupt upgrade to a Divx player. This is likely to affect the acceptance rate and make the overall success of
Divx players a questionable venture. Somehow this begins to feel like yet another VHS versus Beta fiasco.
Direct Stream Digital (DSD)
The move to super storage technology has yet another spin-off proposal. Sony and Philips have suggested the
Direct Stream Digital (DSD) disc as a "super audio CD". The super CD format is going to support the older CD
format to maintain compatibility with the existing CD players. These hybrid DSD discs will be usable in all
current players and will contain additional tracks on the extra storage layer. In order for DSD to become
successful, backward compatibility plays an essential role. This will allow for gradual migration to new
technology and provide additional incentives for consumers. Those with conventional CD players will not get
the full benefits of DSD but will be able to partially use them. So far, DSD is just a proposal, but Sony and
Philips already have prototype systems that they are using to generate interest in the music industry. These
may quickly become a reality since Sony Music is also a music label.
Copy protection
Film piracy has always cost the movie industry a fortune in lost revenue. To fight the number of pirates, the
DVD feature films are likely to be protected with the Macrovision copy protection scheme. Macrovision has
already been used on commercial video tapes which have been on the market for the several years. This should
stop people from being able to copy master DVD titles onto video tapes. Macrovision does not affect the image
displayed on television but the recording with a VCR yields a poor and degraded picture. This does not always
do such a good job as some recorders are only marginally affected.
To fight digital-to-digital copying, Intel, Microsoft and Matsushita have proposed the scrambling of
I-Frames, which are key frames used in digital video. How exactly this is done is not public for various
reasons, but may have something to do with how fast a desktop computer can process scrambled I-frames. This
is perhaps how Microsoft and Intel have managed to get involved. They originally devised the concept and
Matsushita are putting their technology into DVD hardware.
Another piracy protection system will be control of DVDs through manufacturing for certain geographical
regions. Discs purchased within one of eight proposed regions such as the US or Australia would only be
playable by their respective DVD players. This would stop international exports of cheap DVDs from foreign
countries both for DVD players and films. By placing the protection within the hardware and discs, people
would be forced into buying DVD hardware and discs within their geographical regions of distribution. Here
again problems arise, as some manufacturers are said to provide international players capable of playing all
regions.
The future of LaserDisc
For those who are toying with purchasing a LaserDisc, I would recommend DVD technology instead. It boasts
higher picture quality than both VHS and LaserDisc, and the players are much smaller and cheaper to
manufacture. The survival prospects of LaserDisc looks bleak because of the overwhelming benefits offered by
the superior DVD technology. It is said that LaserDisc titles will continue to be manufactured but may begin
to fade out as DVD gains a wider market share. A hint for those who own LaserDisc technology--sell it while
it still has some value and jump onto the DVD wagon.
Selecting a DVD player
As with all new technology, be very cautious about buying the first generation of players. There are already
several flavours of units, ranging from CD-ROM units for your PC from Creative Labs to stand-alone units from
Hitachi. Shop around for something that fits your budget and home environment. Whichever unit you pick, think
of the associated benefits offered by different units. These range from playing all-region DVDs, offering
zooming with Picture-in-Picture (PIP) viewing, built-in surround sound amplifiers (Prologic-AC3), and some
even offer a Pentium 200 under their hood. Those player units with built-in modems can surf the web with all
display being shown on your TV. My best advice is: Use the web to learn more and don't buy the first unit you
see. There are already dozens of units out there and the numbers are growing weekly.
End-user benefits
For the last few years the 650 MB storage capacity has been exceeded by many CD developers and users. Games
and music compilations have appeared on multiple CDs showing the limitations of the humble CD. The new
generation of DVD is addressing those needs with up to 12 times the storage of conventional CD media. It will
prove to be the storage of choice in the near future with more room for video, computer data, and the
possibility of re-writables (DVD-RAMs). This super CD technology is likely to replace audio CDs and domestic
VCRs in the long term. The current high costs will keep the technology out of reach for most audio and video
buffs. As with all new technology, costs will begin to come down to reasonable level as DVD gains more market
acceptance. There is just one more thing before you go out looking for a player. If you think that the future
of video is definitely going to be all digital, then spare a thought for High Definition Television (HDTV)
which is also just around the corner!
About the author
Peter Stanski is a freelance computer consultant and developer. He is currently completing his Ph.D. in
distributed systems, networks and mobile agents.
Reprinted from the February 1998 issue of PC Update, the
magazine of Melbourne PC User Group, Australia
