All about DVD Part 1: DVD Format
Types of DVD and history of development
It's been a long time since DVD became common in our
everyday life. However, most people don't seem to know what it
is exactly. Answers to questions like "what sort of arcane
symbols are printed on disk boxes", "how come DVD is
different from CD if they look so similar", "what kinds
of DVDs are there" and many others still remain mystery for
many users. And instead of making conscious choice they just buy
randomly without any knowledge of what exactly they are
getting.
We will examine DVD in details, along with its history and
different types available on the market. DVD-Video will
get most attention as it is the most common type of DVDs.
What is DVD?
Initially DVD standard was designed for video storage
only. Thus its acronym was decrypted as Digital Video
Disk. Later, when DVD started to become popular for storage
of all types of data, another meaning for DVD acronym was
introduced - Digital Versatile Disk, which is still used
nowadays.
Generally, DVD is the next generation of CD. First of all, DVD
differs from CD by its significantly larger capacity. While CD
disk can only contain between 650 and 800 megabytes, DVD is able
to hold anywhere between 1 and 17 gigabytes, depending on disk
type. This storage increase is achieved by reducing laser
wavelength. But DVD capacity would never reach more than 4.7
gigabytes if it wasn't possible to make DVD disks double-layered
or double-sided.
One side of double-layered disk can contain two layers of data.
To avoid interlapping, outer layer is made semi-transparent.
During reading, laser collects data from bottom layer first, and
then switches to the second layer. This allows doubling the
capacity, up to 9GB. It is easy to recognize double-layered
disks - they have silver shade of working surface, while
single-layered disk appears gold. Most video releases are
printed on double-layered disks.
Apart from that, both sides of DVD can be used to store data.
The possibility of making double-sided disks arise from the fact
that the protective layer for DVD is only half of that for CD,
that is, 0.6mm instead of 1.2mm. So, in order to keep
compatibility with older format, single-sided DVD disks have
additional plastic added to them to achieve 1.2mm thickness. Of
course, it is not a problem to put additional layer instead of
0.6mm of plain plastic. This wasn't possible with CDs as they
are thick enough already.
DVD - the history of conflict
In 1997 several large manufacturers of electronic equipment
established organization called DVD-Forum (earlier
known as DVD Consortium) in order to develop single
standard for new generation of disks, as CD technology was
becoming less and less sufficient.
Despite many debates and lots of technologies claiming to be the
best, the final decision was made and DVD (with eight
types of it) standard was established. It was soon followed by
DVD-Video standard.
However, when it came to standards for recordable and rewritable
disks, several large companies started to push their own formats
DVD+R and DVD+RW. These companies founded their
own coalition called DVD+RW
Alliance. The most interesting part was the fact that
different branches of formats were not compatible with each
other.
Apart from that, Panasonic also
contributed to the mess by developing DVD-RAM standard.
This standard was faster and more reliable, but it was
compatible only with DVD-RAM devices.
The ones who suffered the most from this mess were common users,
as they were forced to make a difficult choice of preferred
technology.
For that reason many people didn't rush for DVD and kept their
data on good old CD-Rs and CD-RWs.
The war of standards was ended by Sony, which made DVD
drive capable of reading both DVD-R\W and DVD+R\W. This device
instantly became popular even in spite of its double price
compared with single-standard drives. Sony soon was followed by
other manufacturers and the ability to read both types of disks
soon became a standard for any DVD drives. This was the
beginning of the DVD era for PC users.
Unfortunately, there also were lots of disagreements during
development of single standard for digital audio,
DVD-Audio. Two technologies compete for the title of
Audio CD heir: a partially compatible with Audio CD technology
from Philips and Sony, and a standalone Toshiba's standard.
Toshiba won, but Philips and Sony didn't give up and released
their own format without DVD-Forum support. This format was
called Super Audio CD (SACD). At the moment both formats
are not selling particularly well and are not known in some
countries at all.
Types of DVD
Let's move to DVD itself. DVD is the most common format
nowadays. At the moment DVD comes in 8 flavors: DVD-1,
DVD-2, DVD-3, DVD-4, DVD-5,
DVD-9, DVD-10 and DVD-18. The difference is
in the capacity, which is denoted by the number in the name
(value is rounded).
The most common formats are DVD-5 and DVD-9. These
are single- and double layered single sided disks, respectively.
DVD-5 holds 4.7 GB of data and DVD-9 is able to
contain up to 8.5 GB. These disks are used for most software and
video releases.
DVD-10 is double sided single layered disk (9.4 GB) and
DVD-18 is double sided double layered disk (17GB). This
two types of DVD are much less common. All four formats
mentioned above have same diameter of the disk - 12cm. Another
type of disk to mention here is DVD-14, which is double
sided disk with one side single- and the other one
double-layered. This type of disk holds 12.32GB of data.
DVD-1, DVD-2, DVD-3 and DVD-4 are
miniDVD. Their diameter is 8cm but otherwise they are
completely compatible with standard drives. As with full-size
disks there are single sided single layered disk (DVD-1,
1.36 GB), single sided double layered disk (DVD-2, 2.48
GB), double sided single layered (DVD-3, 2.72 GB) and
double sided double layered disk (DVD-4, 4.95 GB). All
these disks, except DVD-1, are quite uncommon.
Types of DVD data
Each DVD disk is able to hold various types of data. DVD can be
used to watch movies (DVD-Video), store software (DVD-Data) and
to listen to the music (DVD-Audio).
DVD-Data
DVD-DATA is used to store computer data on DVD. Basically
it is the same CD-ROM, but with much bigger capacity, and it is
used the same way as CD-ROM is. However DVD-DATA is more
convenient as a storage medium due to its large capacity. Most
modern programs doesn't fit on single CD, for example, computer
games and Linux packages often need more than 10 CDs. In case
with DVD one or two disks are usually more than enough. At the
moment software is usually released on both CD and DVD, as not
everyone has DVD drive yet. But it is clear that CD versions
soon will disappear.
DVD-Video
Currently this is the most common type of DVD data, the one that
DVD was initially designed for. Compared with VHS tapes
DVD-Video is a giant leap into the future. There are
heaps of features there that most people have no idea about.
First of all, DVD-Video is interactive - any place on the
disk is instantly accessible and it is possible to have more
than one ending for the movie. And parents can limit viewing of
naughty parts of movies for their children. Apart from that
disks can have additional bonus materials, such as interviews,
promotion trailers, slides, text info and even videogames. In
addition to all this DVD-Video is capable to have multi angle
view option, when camera angle can be changed during playback.
However, this feature mostly used in porno movies and live
concert records.
Video data on DVD-Video disks is compressed by using
MPEG-2 compression. This compression algorithm allows
shrinking video stream approximately ten times, without loss of
picture quality. As a result, each disk is able to hold up to 4
hours of video with 720x576 resolution at 24 frames per second
(PAL) or 720x480 at 30 frames per second (NTSC). The streaming
speed is usually between 3 and 10 MBit per second.
Video can be recorded in different screen ratios. For example,
it can have ratio of 4:3, which is a standard television ratio,
or widescreen - 16:9. Widescreen image have two types: Letterbox
and anamorphic. In the first case image is simply cropped at the
top and at the bottom to achieve desired format. In anamorphic
mode the image is initially recorded in stretched form and then
shrinked to the desired size. This method is much more effective
as whole frame is used for useful data, while in Letterbox large
part of the frame is used to store black pixels only. As a
result, anamorphic mode has better details and sharper
picture.
Audio data can be stored in various formats: LPCM,
Dolby Pro Logic, Dolby Digital, Dolby Digital
EX and DTS.
LPCM (linear pulse code modulation) is uncompressed
stereo or mono soundtrack. It is usually used in musical video
clips and movies where sound clarity is important. Same format
is used for generic Audio CD
Dolby Pro Logic is special type of soundtrack that can be
split into 4 channels for surround sound. Nowadays this format
is uncommon.
Dolby Digital (AC-3) is fully digital sound compression
format; it can be split into up to 6 independent channels.
Unlike Dolby Pro Logic, each channel is recorded on separate
physical track.
Dolby Digital EX is more advanced version of Dolby
Digital. Supports up to 8 independent channels.
DTS (Digital Theater System) is another digital audio
compression format, introduced by Steven Spielberg as an
alternative to Dolby Digital. DTS provides more quality than
Dolby Digital due to lower compression. That, of course, leads
to bigger size of the soundtrack itself, which occupy more disk
space. It also requires special receiver to be decoded. Because
of these reasons DTS disks usually does not have any bonus
materials but have LPCM soundtrack. This soundtrack is included
to allow users without special receiver to listen to the sound
(stereo only, though). Because of all these DTS disks are much
less common compared to Dolby Digital. Usually DTS disks with
improved video quality (and without bonus materials) are called
SuperBit. Both DTS and Dolby Digital (EX) are also used
in cinemas.
Some of the largest drawbacks of DVD-Video are its various copy
protection measures, which were added because of the pressure
from film companies. At first these measures provided lots of
nuisance for users, but eventually every DVD protection was
hacked. This process was also assisted by equipment
manufacturers who simply didn't support most annoying protection
measures.
One of the most annoying of such measures was "Regional
Protection" . The world was divided into 8 zones, and each
DVD player was supposed to have information about its zone. The
same was made for DVDs, and thus DVDs from one zone could only
be played on players from the same zone. User was allowed to
change zone for the player few times only, and the last of
selected zones was locked in the player forever.
This trick was invented in order to be able to assign different
price in each region, depending on income level. Besides, movie
might be released in different times in different countries. For
example, in Africa the movie might just hit cinemas and in USA
it might already be available on DVD. So regional protection was
supposed to stop people from buying DVDs in USA and selling them
in Africa.
Unfortunately, this protection didn't bring anything but
troubles. Many travelers were not able to play disk purchased
overseas. Buying disks over the internet or from EBay also
became a problem. Apart from that, some movies were released in
certain countries only.
Many manufacturers considered these implications and started to
provide means of switching off regional protection for their
devices. Chinese manufacturers basically abandon this protection
at all.
But uncontrolled distribution of DVDs wasn't the only thing that
movie makers were against. Illegal copying was much bigger
problem for them, especially given the fact that digital
information can be copied endlessly without any loss of quality.
To prevent that from happening, manufacturers included special
CSS (content scrambling system) technology in DVD-Video
standard. CSS basically encrypt all disks content and the key
for decryption is available only for DVD-Player or special
viewing program. Simply copying the disk will make the copy
completely useless.
But manufacturers forgot to include support for Unix system and
playback was available only for Windows and MacOS. This issue
was solved by Jon Johansen, who wrote DeCSS program for
Unix that easily bypassed CSS protection. Developers of CSS were
enraged with that and sued Jon. They wanted to stop DeCSS from
spreading and put Jon in prison, however, this case sparked lots
of support movements around the world. Activists even printed
DeCSS code on t-shirts. Finally, Jon was declared not guilty and
his program laid a foundation for many DVD copy utilities all
over the world.
In general, DVD format was successful and, despite some issues
with regional protection, has spread all over the world and
almost replaced VHS tapes.
Summary
DVD is not a new format anymore and there are actually new
formats already that aim to replace it. Someone could ask why
does he or she needs to be familiar with DVD if there is
something new coming? The answer to this lies in the fact that
DVD provides foundation for most new technologies, for example
HD-DVD or Blue Ray. And if someone became familiar
with underlying principles once, it won't be a problem to switch
to something new later.