The Digital Versatile Disc, or DVD for short, is one of the most useful inventions of the later half of the decade. Utilizing better compression and more advanced technology than any of it's previous competitive media types, the Digital Versatile Disc is a tool that can be used by anyone for anything. Hollywood movies, music albums, DVD-ROM games, and volumes of encyclopedia knowledge are some examples of the many versatile uses of this wonderful new media. DVD has its good sides and its bad sides, but unlike most other things it even has a third and fourth side in between!
The DVD is the latest and greatest widely available technological achievement in media storage and retrieval. Image preservation is the oldest form of media storage and has been around since the cave people. The written word was the next progression in the world of media. Sound recording and playback was the first media form that could not be seen. Beginning in 1877 with the phonograph, the first speech sample was recorded and played again later by Thomas Edison. Next came the record, the eight-track tape, and audiocassette. The next revolution was the preservation and replication of moving video. The VHS tape (Vertical Helix Scan) was the first form of mass production video media that was available for public use. The next development was the audio Compact Disc that was introduced in 1982 by Sony. Three years later Sony and Phillips cooperated to produce the first CD-ROM, which was to be used for data storage on computers. In 1990, these companies introduced the Compact Disc-Recordable, which brought CD burning technology to the public. Five years later Re-Writable Discs were standardized, which allowed CDs to be read from and written to multiple times. In 1996 many media corporations, lead by Sony and Panasonic, cooperated and finalized an agreement on a video format for the new Digital Versatile Disc. A year later, the first players were available in the United States.
One of the biggest factors that made the DVD a convenient invention is its physical characteristics. Measuring in at exactly the same dimensions as the Compact Disc makes it deceptively familiar to anyone who owns or has operated a home entertainment system, "Boom Box", or Discman. While it occupies the same amount of physical space as its older brother, DVD contains vast amounts more of virtual space. This is accomplished using more refined digital transfer technology involving optical lasers and disc stamping techniques. (Disc "stamping" is the term used to describe how a disc is mass produced.) Illustrated in the pictures to the left and right are highly zoomed comparisons between the two types of discs: CD-ROM on the left, DVD-ROM on the right. Utilizing a different kind of laser and more precise optical lenses a DVD is able to compact many more "pits" and "lands" (holes and flat spots, respectively) into the same amount of space. The actual dimensions of the Compact and Digital Versatile Disc are 120 millimeters (4.75 inches) in diameter and 1.2 millimeters thick. However, the DVD can utilize both of its surfaces and each of those is made up of two thin substrates that allow it to hold up to a massive 17 gigabytes. As the picture indicates, the shortest pit length for a CD is 0.83 micrometers. For the DVD they have managed to cut that into less than half, making the shortest pit length 0.4 micrometers. The distance between the tracks (referred to as "track pitch") is 1.6 micrometers on the CD, and 0.74 micrometers on a DVD, a considerable shrinking achievement. Another characteristic of both the DVD and CD are their high durability: they are resistant to dirt and fingerprints as well as impervious to magnets and light.
The Digital Versatile Disc supports many features:
Before the DVD standard was finished and before there was a working prototype, it had proposed so many features that people refused to believe that it would be able to deliver. One avid critic said "DVD movies are supposed to have features such as multiple aspect ratios, and different languages and ratings and subtitles. There is really no true hope that any of these features will come to pass on general release." [firstname.lastname@example.org on newsgroup alt.video.laserdisc] DVD has delivered on all of these counts. He also said "I seriously doubt that most stores will offer DVD for rent for longer than 2 months after the launch." His opinions were not that unreasonable since there have been other attempts at making a universal media type such as the DVD, each receiving mixed results. But none had anywhere near as good a reception as the DVD did.
The Digital Versatile Disk can be used for very many purposes including every imaginable type of media. What gave the DVD its popularity was the movie industry. Anyone walking into any video retailer and looking through the rows of DVD Videos available to purchase or rent can see this. DVD was designed to compete with and eventually replace the extremely popular VHS tape, the Laser Disc, as well as the Video CD (which is not commonly found in the US).
Below are two pictures taken from the movie Bladerunner, The Directors Cut (© 1991 The Bladerunner Partnership). We apologize for the use of super high quality bitmap pictures below which will take a long time to download and will only be visible in Internet Explorer 4 or greater, but they were needed for the quality we needed to show. (If you are using netscape, follow the link listed below the pictures) For something to focus on, try to distinguish the two people sitting or standing at the table at the center of the frame. Note that with video imagery it is extremely easy to fake low quality effects, and for a definitive comparison it is necessary to look at a real DVD and VHS player that are playing at the same time on two near-by TVs.
Sample VHS Frame
Sample DVD Frame
For more info on these pictures, click here (external link).
The DVD is superior in all ways to its predecessors because of the advanced data encoding that allows for higher quality recording. DVD comes closer to approaching "D-1", the CCIR-601 TV studio production standard for picture quality using MPEG-2 video compression which allows for 500 lines of horizontal resolution. The Laser Disc provides 425 lines, Super-VHS has 400, and regular VHS gives only 240 lines of resolution. MPEG-2 is a video compression standard approved by the Motion Pictures Experts Group in 1994 and is an International Organization for Standardization (ISO/IEC) standard (13818-1). Links to more information on MPEG are available below.
A simple description of MPEG is that it is an encoding scheme that uses compression to store video data. MPEG has two different steps. First, it examines the image data for redundancy and removes this. Around 97% of most video signals are not needed and can be discarded. The second step is to encode the remaining data, which MPEG does without losing any picture quality. This two step process allows for more efficient bit rates. Since this process is done dynamically for each picture, a variable bit rate is generated, with higher bit rates (max 10Mbps) needed for complex pictures and lower rates (around 3.5Mbps) needed for simpler pictures. Without MPEG compression, if desired to reproduce the CCIR-601 studio quality recordings, the bit rate would have to be a tremendous 167 megabits per second. This would only allow for around 4 minutes of video on a single sided, single layered DVD. [www.sony.com]
Similarly to the Laser Disc, the DVD is an optical media. This means that they use lasers to decode the information they store and never come into physical contact with the devices that read from them. VHS tapes are a magnetic media; they use magnets that must make physical contact with the tape and the player. This physical contact causes a loss in quality over time. A nice feature of optical media is that it does not suffer from this degradation over time. Another problem with magnetic media is that since it actually temporarily pulls the tape out of its housing, if the player has a malfunction it could cause serious damage to the tape. Similarly optical media can easy be damaged by scratching if users are not careful.
Just as this new technology provides a significant improvement to video quality, DVD also allows a drastical increase in sound quality. Dolby Digital (also known as AC-3) is the newest standard in high quality sound systems, used by production studios, theater companies, and home theater buffs everywhere. This standard consists of 6 channels, providing discrete sound for each of the four corners, center, and subwoofer speakers. Compact Discs are only capable of providing normal stereo sound, which provides discrete sound for two separate speakers. The illustration to the left gives a comparison of these two speaker layouts. At the same quality, DVD allows for at least 7 times as much music as an ordinary CD. This could allow for volumes of music, which span multiple CDs, to be condensed onto one DVD.
DVD technology provides a great leap in audio sampling quality, and is capable of reproducing much higher fidelity (or accurate) sound and video. As the figure below and on the left shows, DVD is capable of generating over four times the sampling frequency and significantly higher quantization levels. While in nature there exists an unlimited number of frequencies and sample levels, we are limited by our technology as to the number we are capable of recording. DVD will increase this limit to 192 kHz, a vast difference compared to its predecessors. The compact disc that we are all familiar with provides sound at 44.1 kHz and cuts out everything else. The highly popular MP3s (which stands for MPEG-3) use a similar technique of cutting out frequencies that are harder to distinguish, but does this dynamically instead of at a set frequency of 44.1 kHz. Old records could provide more quantization levels than CDs when new, but since they were analog and used physical contact to reproduce the sounds they contained, they wore out and the quality degraded with each subsequent use.
Another improvement with the DVD is that it is capable of producing 144 decibels of sound, which is much better than the 96 dB output capacity of the CD. This means the DVD can produce louder noises and quieter silences.
On a side note, Srikanth Narayanan performed an interesting experiment comparing the audio quality of a VHS tape to that of a Compact Disc. Follow this external link for more information.
One of the most crucial reasons that DVD can be considered a wonderful new technology is its ability to store vastly more data in the same amount of physical space. In its simplest state the DVD offers the data capacity of more than 7 times that of a CD or thousands of floppy discs, as well as a little more video time than a VHS tape (in SP mode) but with better quality. These discs have several states which offer even more storage capacity. There are four versions of Digital Versatile Discs, as illustrated below.
Part of what allows the DVD to hold so much data is its ability to store information on two layers per side. This is not possible with an ordinary compact disc because a CD is made of a thin layer of aluminum. When a DVD laser reads the surface of the disc it is designed to be able to change wavelengths to look through the first layer and read the second layer. This process is similar to placing many layers of glass perpendicular to the direction you are facing, and then changing the focus of your eye so you can look at the different layers. However, unless you have a DVD player that can read both sides of a disc at once, you are required to take the DVD out and flip it over in order to use the second side.
One of the more visible differences between a CD and DVD player are the "color" of the laser used to read the pits and lands off the discs. Compact Disc players use an invisible infrared laser that has a wavelength of 780 nanometers. Digital Versatile Discs use a red laser with wavelength of either 650 or 635 nanometers, depending on which layer of the disc is being read. You may see page 75 in our textbook for Figure 4.14 Electromagnetic Spectrum for Telecommunications, which is a chart of the wavelengths in the light spectrum. The lower far right corner of the figure is what is relevant to us here.
Another advantage that DVD holds over CD is that at base transfer rates; DVD is capable of transmitting almost seven times as much data per second as a CD. The DVD can read a burst rate (maximum) of 9.6 megabits per second and an average transfer rate of around 5 megabits per second. This compression, along with a new error correction technique (called Reed Solomon Product Code, or RS-PC) provides for extremely fast response times. Just as CD-ROMs are continuously advancing in speeds, as visible with the 2X, 4X, 8X, and such drives, the DVD-ROM drives will also follow this pattern. Because of this actual transfer rates will vary considerably depending on the maker, model and speed of the drive. Even with faster drives video quality will not increase since all you will ever need to play a DVD movie is a single speed drive, just as with an audio CD you only need a single speed CD-ROM.
Another one of the really impressive advancements of DVD technology is that it allows for a union of the home entertainment system and the personal desktop computer industries. There have been attempts at this in the past with the Video CD, which was significantly lower quality than VHS and especially Laser Disc, and was not successful in the United States. Now, with the monstrous storage capacity of the DVD and more efficient transfer speeds it is possible to put entire, superior quality videos onto one disc. Since the DVD is such a convenient size and is digital, it is very easy to get a DVD-ROM drive for a PC that performs all the functions of a home entertainment DVD unit. This was no much more difficult in the past using analog tapes.
The introduction of this new technology to the computer industry has lead to new hardware and software developments. DVD viewers have a choice as to whether they want to use hardware or software to decode their movies on their personal computer. More and more video card manufacturers are providing video cards that are capable of displaying DVD movies using software algorithms. The other option is to use a dedicated hardware device whose only purpose is to decode DVD videos. Of course the added hardware costs more (about $50-100), but the benefits are great. Shown in the figure to the right is a comparison of processor utilization with either software or hardware coprocessor decoding. This figure shows that dedicated hardware frees up CPU time tremendously, which allows the user to perform multiple tasks at the same time such as word processing, world wide web browsing, or gaming while simultaneously watching a DVD movie. Another feature of having a DVD-ROM drive in your computer is that with proper hardware capabilities it is possible to watch the DVD output on either a monitor, TV, or both at the same time.
The DVD does have some disadvantages. One of the major disadvantages DVD is facing is it is only available in the DVD-ROM version, and not the DVD-RAM. DVD-ROM means Digital Versatile Disc Read Only Memory, and limits all of its capabilities to reading from prerecorded material. It is not possible to write to this type of media. DVD-RAM (DVD Random Access Memory) will allow us to do this, but the technology is either not developed fully or has not been adopted by manufacturers yet. Creative Labs is the only company we could find that does offer a PC-DVD-RAM, and it costs $300. Recordable media costs $200 for a pack of five (this is competative with the Iomega Jaz drive which supports 2 Gb proprietary discs). Strangely this media is only capable of using 2.6 gigabytes per side (out of a possible 4.7) and no layering is available. Until DVD-RAM becomes widely available and affordable, we will not be able to record TV programs, home movies, or custom made music from the television, home video cameras, or your personal computer. Another problem with DVD is that you have to be careful not to scratch, touch, or get dirt on them; otherwise, you can cause serious damage to the disc. This could possibly cause you not to be able to read the data on the DVD. Users should be familiar with this since it is the exact same problem that was present with the Compact Disc.
Whenever a new form of media is developed, the people who will be selling it always want to make sure it can not easily be copied. Some VHS tapes have special magnetic encoding that discourages illegal dubbing. The copy protection for Compact Discs for a long time was that it was uneconomical to try to copy a disc since it cost hundreds of dollars. Currently, with the rapidly falling prices for CD-ROM Burners, there is no copy protection on audio or data CDs. Knowing how easy it is to illegally copy digital data, the makers of the Digital Versatile Disc did not find it acceptable to release the technology without some sort of strong copyright enforcement technique. There were two groups that held much interest in how this would be done; the computer and the movie studio industries. Computer manufacturers wanted very easy to decode encryption so that it would take less processor power, which would allow for better multitasking. Hollywood, on the other hand, wanted very tough and complex encryption sequences which would safeguard its copyrighted material. A compromise had to be achieved, and two organizations were responsible for this: the Consumer Electronics Manufactures Association (CEMA) and the Copyright Protection Technical Working Group (CPTWG). The final decision was originally proposed to these two organizations by the DVD Consortium, whose purpose was to organize the details of all the technological specifications of the DVD. The consortium modified an earlier proposal that had come from the computer manufacturers IBM and Intel. What was decided was in order to conserve computing power, they would encrypt only some of the frames in the video set (these special frames are called I-frames) along with a few other randomly chosen frames in between. This is remotely similar to what current Pay-Per-View cable companies do, which does not scramble the entire signal, but rather renders the movie so distorted that it is basically unwatchable without the decryption key. A benefit of using this scheme instead of the tougher one insisted upon by the movie industry is that this simpler scheme, while getting the job done, avoids federal regulations which prohibit exportation of advanced encryption technologies outside of the country. [www.newmedia.com & www.cemacity.org, see below for specific links]
Other applications of the MPEG-2 video compression scheme include digital television and digital cable. Digital Television is a new form of television transmission that will replace the existing analog television in only a few years, and is also referred to as HDTV (High Definition Television). Digital transmissions are already available through satellite service providers (referred to as DSS providers) such as DirecTV, and via digital cable companies such as TCI. Group M discussed MPEG-2 in their project on Digital Cable last spring. This fall, Group 12 is discussing Digital Cable, Group 3 is focusing on Digital Image Processing, and Group 25 will teach us about Digital / Analog Technology. Each of these will have some relationship to MPEG-2 encoding and will either influence or be influenced by DVD.
The release of DVD came at a perfect time to coincide with the industry growth of Internet based electronic commerce. Retailers and discount stores who want to sell books, CDs and DVDs are popping up every where on the world wide web. The release of DVDs, which are as popular among home computer users as with the rich home entertainment system owners, are extremely popular since they allow computer geeks and novice users alike to watch high quality movies on their computers. This is a novel idea that will last for many years. There are countless DVD web sites available which provide everything from movie reviews, disc reviews (special feature overviews and commentaries), drive comparisons, software player downloads, and online order forms. Group A discussed digital cable technology more thoroughly in their project last spring. This fall, Group 26 is focusing on E-Commerce & On-Line Stores, and Group 27 will discuss Internet Security with E-Commerce Security. The successful sales of DVDs across the web will be very influenced by the topic these two groups are covering.
As the name implies the Digital Versatile Disk can be used for any purpose involving digital data and will be the preferred method of storing multimedia for many years. DVD has a good chance of replacing all other audio media devices just as the CD did when it came out. DVD will also come to dominate the video industry as the major media used when all TV programs are sent out digitally. Once DVD-RAM becomes available then it will be as easy to digitally record television as it is to record current analog programs with a VHS recorder. Since DVD has so many uses it should easily become the preferred way most data will be stored and transferred from PC to PC. Plus, in order for a computer to be labeled as "Designed for Windows 98" it is required that a DVD-ROM drive be part of that system. So DVD has already gotten a solid hold on the market. One thing that can be assured, however, is that just as the CD-ROM topped the Floppy Diskette, and DVD topped the CD, another media will come along in a few years to that will be better than DVD. Even so, just as cassette tapes, floppy discs, and even records are still available, Digital Versatile Discs will be around for a very long time.
We were able to find many sources of information on the world wide web. Very little specific citing has been done within our document because much of the information was repeated throughout many of these pages. There are a couple citations listed above, denoted with the [square brackets]. All pictures displayed on this page have references to where we got them in each pictures alternate text. We e-mailed one person who had some negative opinions on DVD before it was finished, but we did not receive a response. We have chosen the more interesting and better presented sites in the links below. All are active (not broken) at time of project submission on Thursday, December 9th, 1999.