Transcript
DVD Authoring The Hardware Aspects of The DVD And Its Authoring Process
The development of optical drives, such as the CD-ROM (Compact Disc, Read-Only Memory), in the 1990s greatly expanded the power of the PC. Software developers could store much more information in less space. For the first time, including video clips in software was a practical option, making the PC a multimedia machine. Consumers could also record and back up large amounts of data conveniently, thanks to the arrival of CD-R (Compact Disc, Recordable) and CD-RW (Compact Disc, ReWritable) drives. 1.44MB (megabyte) diskettes could not compete with this powerful new tool. Now we have entered another optical drive revolution: the DVD (Digital Versatile Disc) revolution. DVD could soon do to CD technology what CD technology did to the diskette drive, and turn it into a nearly obsolete storage medium that almost no one uses regularly for storing and backing up data. DVD is superior to the various CD technologies in nearly every way possible. DVD provides much better video and audio, offers several times the storage capacity, reads every CD format in addition to DVD format, and in many cases is even faster than current CD drives.
How DVD Drives Work The operation of a DVD drive is quite similar to that of a CD drive in most respects. For example, DVD drives read DVD media the same way that CD drives read CD media. Both CD and DVD media contain bumps on their surfaces called pits. The smooth spaces between the pits are referred to as lands. The DVD drive focuses a laser on the surface of the DVD disc. The DVD drive measures how much of the laser light is reflected back. When the laser passes over a land, most of the light is reflected back to a sensor in the DVD drive. The drive knows the laser has just passed over a land because of the intensity of the reflection. When a laser passes over a pit, much of the light is diffused. The sensor interprets less reflected light as a pit. The pits and lands are equated with ones and zeros that make up the binary language of
computing. The DVD drive then sends this string of ones and zeros to the computer so it can process the data. The way DVD drives read discs is hardly the only thing they have in common with CD drives. They also share many of the same features, with minor differences. For example, one of the most important performance indicators for both CD drives and DVD drives is the data transfer rate, or how quickly the drive can transfer, the faster the drives moves data from the disc to the computer. Both CD drives and DVD drives measure the data transfer rate in KBps (KiloBytes per second).
DVD Storage Capacity Although having the same physical dimensions of a CD, the DVD has a much higher storage capacity than the CD. The DVD has taken storage capacity to a new level. It was first called Digital Video Disc, but because of its computer usefulness as a storage medium as well, it has been renamed to Digital Versatile Disc. Entire movies, in high resolution MPEG-2 video, can be stored on a single DVD, including clips from behind the scenes, and options to have the movie’s audio switched to different languages, including subtitles in up to 32 different languages. The DVD's incredible storage capacity has allowed the film industry to distribute their movies and videos with more freedom. Movies on DVD are digital and are much more clearer and sharper than that of VHS. Options such as wide screen, full screen, and letterbox format, which before were impossible to implement into movies on VHS, can now be possible thanks to DVD’s incredible storage capacity. Nothing but a laser light touches the DVD surface, so the quality won’t degrade from physical damages of the player. There are several reasons why a DVD can store more information than a CD. First of all, the pits on a DVD are “squeezed” more tightly together. The pits on a CD are .83 microns in diameter while a DVD pit is .4 microns (about half that of a CD). Second, the DVD tracks are closer together. Distance between tracks on a DVD is .74 microns, while the distance between tracks on a CD is 1.6 microns. Then we have double sided and double density forms of DVD, where the information can be written on both sides of the DVD and has two different layers of information per side, respectively. The laser in a DVD player adjusts its wavelength slightly to read data from one layer or the other.
DVD Media Storage Capacity Single-Sided, Single Layer Single-Sided, Double Layer Double-Sided, Single Layer Double-Sided, Double Layer
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4.7 Gigabytes 8.7 Gigabytes 9 Gigabytes 17 Gigabytes
DVD Formats DVD technology, like CD technology, comes in several formats. Different technical specifications, called books, define the different DVD standards. The DVD Consortium, now called the DVD Forum, set these standards in the mid-1990s. DVD technology consists of five books: DVD-video, DVD-ROM, DVD-R, DVD-RAM, and DVD-audio. The most used DVD specification is that of DVD-video. Thousands of movies are available in the DVD-video format, and the sale of DVD players has increased dramatically over the past year. The DVD-video book defines the specifications for movies stored on DVD media. DVD-video media follows the MPEG-2 (Moving Pictures Expert Group) video standard that provides very high-quality picture and sound. DVD-video media can store at least 133 minutes of Mpeg-2 video, which is enough for a full-length movie. DVD-video also uses Dolby Digital sound. DVD-ROM is similar to DVD-video. Both standards offer the same amount of storage, and you can watch a DVD movie on your computer, as long as you have a DVD-ROM drive and a hardware or software MPEg-2 decoder. DVD-ROM is read-only media, which means you can’t record data to it. However, DVD-ROM drives can read just about ever type of optical disc, including audio CDs, CD-ROM, CD-RW, video DVD, and DVD-ROM of course. DVD-RAM is the DVD equivalent of CD-RW. You can record data to it and rewrite over that data several thousand times. DVD-RAM media can store much more data than CD-RW media. DVD-RAM drives typically record data faster than a CD-RW drive, but tend to have slower data transfer rates than DVD-ROM drives. DVD-RAM media comes in two forms: single-sided 2.6 gigabyte discs are also known as Type 1 DVD-RAM media. The disc is encased in a cartridge that looks similar to a Zip disk case. But the disc cannot be removed from the cartridge. The 2.6 gigabyte discs are known as Type 2 DVD-RAM media. These discs are also stored in a cartridge, but you can remove them from the cartridge. The latest DVD-ROM drives can read Type 2 DVD-RAM media if it is removed from the cartridge.
DVD R and CD RW: As with regular DVDs, the DVD+R/+RW and DVD-R/-RW have a polycarbonate substrate, a reflective layer, and a protective top layer. In between the substrate and reflective layer, is the recording layer composed of an organic dye. Unlike the regular DVDs, a “pre-grooved spiral track” is used to guide the recording laser along the spiral track. This greatly simplifies CD recorder hardware design, ensuring disc compatibility. A pressed DVD has reflective and barelyreflective areas, referred to as "lands" and "pits", respectively. A laser in the DVD recorder makes the marks in the disc's dye layer that have the same reflective properties. The pit and land patterns on the disc, encodes the information and allows it to be retrieved in a DVD-ROM drive or player. The difference between a DVD RW and DVD R, is that the DVD RW is not made up of the regular pits and lands. Instead, the state of the recording layer in a DVD RW changes from crystalline to amorphous form. The different states have different refractive properties, either reflective or non-reflective, and thus simulates the pits and lands of a DVD and DVD R. To erase the data on a DVD RW, the refractive property of the recording layer is simply reset back to its original state by the laser.
As you may have noticed, there are two different standards of DVD mediums for recording: the “plus” and the “minus”. Although similar in function, the DVD+R/+RW standard (“plus R / plus RW”) outperforms the DVD-R/-RW standard (“minus R / minus RW”) in terms of its features and versatility. Over the next two pages, are two tables comparing the differences between the two standards.
Comparison Tables Between DVD+RW and DVD-RW: DVD+RW
DVD-RW Compatible mode
Feature
Divide title afterwards (manual making of titles) Manually add chapters afterwards Hide chapters / create playlist Partial overwrite old recordings
Yes
No
No
Yes
No
Yes
Yes
No
Yes
Yes
No
No
Add new recordings to Yes - always a (compatible!) disc Erase old recordings
Yes - any title
Not needed, always immediately compatible Automatically updated Yes - Updated after picture menus each recording Edit recordings on Yes same disc using PC Variable Bit Rate Picture quality always Recording time 1 - 4 or 1 - 6 hours 1) (per side) Time needed to change recording mode, or re- Not required use finalized disc Finalising time
DVD-RW Non-compatible mode
No (only on unfinalized incompatible discs) Only last title (on unfina- lized incompatible discs)
Yes
Yes
5 - 15 minutes
5 - 60 minutes
No
n/a
No
n/a
Constant Bit Rate Variable Bit Rate (VBR on some models) 1 and 2 hours only 1 - 6 hours (1 -6 on some models) 1 minute
1 minute
Comparison Tables Between DVD+R and DVD-R:
DVD+R
• Feature
DVD-R
Picture quality
Variable Bit Rate - always
Constant Bit Rate or Variable Bit Rate
Finalising time
1 minute
5 - 15 minutes
Manually add chapter stops during recording
Yes - DVD-Video compatible
No
Manually add chapter stops after recording
Yes - proprietary
4)
No
Editing (define playlist of chapters)
Yes - proprietary
4)
No
Index picture menu on DVD player
Yes
No (Yes - on some models)
Unfinalized discs are interchangable between recorders
Yes
No
As you can see, the DVD+ is leading the way in terms of setting the acceptable standard for the DVD recording medium. All we need now is time for the different recordable DVD standards to iron themselves out, and to agree on a more universal standard. We are being bombarded with several concepts, but so far the DVD+ standard is the recordable DVD of choice, and will most likely be the big influence in the final say for the recordable DVD standard.
Manufacturing: The disc is made of a clear polycarbonate plastic, which initially is set to a high temperature to allow it to be in a molten state. It is then molded into its circular shape, with one side of the disc being stamped with millions of microscopic pits and then being coated with a fine layer of aluminum. The film is then coated with an equally fine layer of plastic. This is the side with the disc that is scanned with the laser beam in the DVD-ROM or DVD player. The scanning is done from underneath. On the other hand, some discs are made of optical glass instead of plastic.
Cleanliness is an essential part of the making of a CD. Dust particles can be as dangerous as a stalled car on a railroad crossing. The room to make CD’s is clean, has no windows and the air brought into the room is completely controlled. The room has the dust particles precipitated, and the air is washed and dried, thus when it enters the room, it has only two or three particles of dust in a cubic foot of air.
CDs and DVDs are written from the inside of the disc outward in a spiral formation. If you "unwound" the spiral of a 4.7gig DVD, it would be roughly 25 miles long!
Production
of discs can be listed under two main headings: mastering and molding
Mastering: • Mastering process begins with the work of polishing a plain glass optical disc. • Disc goes undergoes various cleaning and washing steps (including supersonic cleaning). • Disc is under strict quality control to ensure that defects such as scratches and dirt do not exist. • If the disc passes inspection, it is then polished. • The glass is then coated with a thin chrome film. This produces adhesion between the glass and a photosensitive material (photo-resist). • Two products are joined now. The first is the binary coded signal recorded on the DVD master tape and the other is the glass disc. • The data on the DVD master tape is now transferred to the glass disc by a laser beam cutting method. • The pits are formed by photographically developing the glass disc. • The glass disc undergoes a nickel evaporation process. This makes the surface electrically conductive. • This stage the disc is called a glass master and undergoes more inspection, for such things as electrical characteristics and dropouts. • Dropouts are lack of pit formation or pits in areas that should be flat. • The glass master undergoes nickel elctrocasting (copies the microscopic pits). • The disc undergoes a series of metal replications resulting in a disc called a stamper. • Stamper is a reverse of the final DVD. It has bumps instead of pits. • Stamper is used to make the final copies of the DVD. Molding : • Molding uses the stamper disc (which is equivalent to a negative) and creates the positive. • The disc now has pits and flats. • This undergoes an aluminum evaporation process. • This strengthens the pits and flats to avoid deformation of the plastic. • A reflective surface is needed to deflect the laser beam for reading. • The aluminum is deposited as a fine layer. • To protect this reflective aluminum, a UV ray hardened resin is coated over the aluminum film. • This resin provides erosion and corrosion resistance and excellent bonding ability with the aluminum. • The disc label is finally printed. • The label is applied directly over the protective layer surface with the same resin used as the protective layer.
The future of DVDs seems promising. CD-RW drives may be all the rage for now, but DVD+R/+RW is expected to surpass it in the next few years as prices for DVD manufacturing drop. When that happens, the DVD will give CD-R/RW a serious run for their money as the storage option of choice. Dataquest estimates that by the end of 2003, DVD-ROM shipments will reach a hefty 106 million. DVDs have been one of the most exciting and important technologies to hit computing since its predecessor, the CD-ROM drive. DVD has everything a serious computer user could want: massive storage, great speed, and relatively low prices, and it’s ideal for all things multimedia. This is what computing was meant to be.
Bibliography
How Stuff Works - "How Are Movies Stored On DVD discs?" http://electronics.howstuffworks.com/question596.htm How Stuff Works - "How Does A DVD Work?" http://entertainment.howstuffworks.com/question61.htm How Stuff Works - "What Is The Difference Between DVD-Audio And CDs?" http://electronics.howstuffworks.com/question344.htm The Reference Website For MPEG! http://www.mpeg.org/MPEG/index.html Discover The Power Of DVD ! http://www.mpeg.org/MPEG/dvd.html DVD Authoring http://www.rsrt.com/dvd/authoring.html Buyer's Guide: DVD Writers http://www.smallbusinesscomputing.com/buyersguide/article.php/1026541
