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-RW and DVD+RW. 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.
By : Artem Chlegov
Keyword : all about dvd,dvd-hd,blue ray,audio-cd,dvd-video,dolby digital,dts,formats,dvd-data,micro-d
