OPTICAL DISC FUNDAMENTALS
Data stored in binary form, composed of strings of “ones” and “zeros,” can represent anything that can be stored digitally for computer use: images, video, sound, or text. Optical discs such as the DVD (Digital Versatile Disc) store data as a series of microscopic indentations (known as “pits”) in the disc surface. The disc drive or player reads these pits as binary data by reflecting a laser beam off the spinning surface.
Replicated discs such as DVD-5, DVD-9, DVD-10, and DVD-18, which are sometimes called “pressed” discs, begin with a process called glass mastering. During glass mastering, a stamper containing the data is created, and is then used to injection-mold the discs. These “pressed” discs have their data encoded as a series of microscopic indentations molded directly into the disc surface. The resulting disc is only half of a finished DVD and is half as thick as a normal disc. The process is then repeated to make the other half of the disc. The two disc halves are then metallized, usually with aluminum, which gives the discs their silver color. The process is completed when the two halves are bonded together to create one complete DVD. Artwork is silk-screened onto the disc after manufacturing. The replication process takes place in a manufacturing facility and is how all retail-ready products are produced. Replicated discs have virtually 100% compatibility with DVD playback devices.
Recordable DVDs (DVD-R and DVD+R) differ from replicated DVDs in that their data is not stored as actual indentations, but as laser marks made by burning tiny holes in the dye layer of the DVD-R media. Other related storage technologies such as DVD-RAM create the equivalent of pits by heating a crystalline layer, which becomes non-reflective where the laser strikes it. Changing the intensity of the laser beam can return the surface to the equivalent of a non-recorded state, allowing the media to be revised up to 1,000 times. The various recordable formats are available to the public for easy and inexpensive creation of small quantities of DVDs. DVDs created this way are called “duplicated” as opposed to “replicated” discs.
TYPES OF DVDs
It’s important to understand the difference between the physical formats (such as DVD-ROM and DVD-R) and the application formats (such as DVD-Video). DVD-ROM is the base physical format that holds data and is universally playable in the DVD-ROM drives featured as standard equipment in most new computers. DVD-ROM also includes recordable variations: DVD-R/RW, DVD-RAM, and DVD+R/RW. DVD-Video (often simply called DVD) is an application format. This format defines how video programs such as movies are stored on disc and played in a DVD-Video player or a DVD computer.
DVD-Video discs, designed for playback in both set-top DVD players, as well as computer DVD-ROM with the necessary decoding circuitry or software, deliver crisp, clear digital video content and sound at a level comparable with audio CDs. DVD-Video can hold anywhere from 4.7 GB (DVD-5, single-sided, single-layered) to 17.9 GB (DVD-18, double-sided, double-layered). The DVD-Video standard also provides a degree of interactivity that can lead viewers to different types of content and activate certain features, such as a different language version of a movie or the director’s commentary on the movie features.
TYPES OF RECORDABLE DVD MEDIA
There are currently six recordable versions of DVD. Three can record data once: DVD-R for General, DVD-R for Authoring, and DVD+R; three can be rewritten thousands of times: DVD-RAM, DVD-RW, and DVD+RW.
The DVD-R and DVD+R formats are typically used for one-offs and short-run duplication. These discs are a write-once form of media; once you record the data, you cannot erase or rewrite it. Artwork is typically applied with an inkjet or thermal disc printer after duplication, but custom-printed blank media can be obtained as well. Disc Makers offers silk screen printing on DVD media.
The DVD-R format comes in two varieties: authoring and general-use. Authoring media is more expensive and can only be recorded in discontinued authoring drives. Because of this, use of authoring media is rapidly declining, and it will likely become obsolete in the near future. General-use DVD-R offers lower cost and faster write speeds than authoring DVD-R, and it shares the market with the DVD+R format.
The DVD+R and DVD-R formats are very similar. Theoretically, both offer the same playback performance and compatibility. Until recently, DVD-R could only be recorded on DVD-R drives, and DVD+R could only be recorded on DVD+R drives. Why are there two formats? Which one is better? Basically, the industry group that created DVD+R did so in order to avoid paying royalties to the group that created DVD-R. For a while DVD-R was the clear choice due to lower media cost and higher compatibility with players, but this has equalized. It is likely that the two formats will continue to co-exist. Fortunately, consumers will not really be affected by this “format war” due to convergence in the recorder market. The trend is that most DVD recorders will become dual-format DVD±R devices which will record both DVD-R and DVD+R discs.
The ability to create DVD one-offs has made DVD recorders popular with developers, business users, hobbyists, and filmmakers. Many replication services (including Disc Makers) accept properly mastered DVD-R one-offs as source material to begin the manufacturing process.
A brief summary of the various formats is below:
-DVD-R. Pronounced “dash R,” not “minus R.” A write-once format, compatible with about 90% of existing DVD drives and players. Can be used as a replication master.
-DVD+R. A write-once format, compatible with over 85% of existing drives and players. Cannot be used as a replication master.
-DVD-RW. The rewritable version of the DVD-R standard. Not suitable as a master for replication. Compatible with about 70% of DVD drives and players.
-DVD+RW. The rewritable version of the DVD+R standard. Cannot be used as a replication master. Compatible with about 70% of DVD drives and players.
-DVD-RAM. A rewritable format that is typically used for data storage applications. This format generally uses a cartridge transport and is incompatible with standard DVD drives and players.
Compatibility is still somewhat of a problem with recordable DVD formats. As in the early days of CD-R, some players and drives can have difficulty reading recordable DVD discs. As these devices are replaced within the next few years and increasing numbers of new, compatible playback devices are sold, recordable DVD playback compatibility will approach 100%. For compatibility lists, visit DVDMadeEasy.com, DVDRHelp.com, or DVDplusRW.org.
DVDs, depending on the format, can handle from 4.7 GB to 17.9 GB. This is because DVDs can be either single-sided or double-sided, and each side can have one or two layers of data. By comparison, a CD-ROM only holds about 700 MB.
Some different formats are listed below:
-DVD-5, DVD-R, and DVD+R. Single-sided, single-layer. Holds 4.7 GB of data (about 2 hours of video).
DVD-9. Single-sided, dual-layer. Holds 8.54 GB of data (about 4 hours of video).
DVD-10. Dual-sided, single-layer. Holds 9.4 GB of data (about 4.5 hours of video).
DVD-18. Dual-sided, dual-layer. Holds 17.08 GB of data (about 8 hours of video).
Almost all players and drives read dual-layer discs, and all players and drives also play double-sided discs if you flip them over. Most replication plants now have the capability to make dual-layer discs, although they are generally more expensive to produce (about 10 cents more per disc).
HOW MUCH VIDEO WILL FIT ON A DVD?
While a good rule of thumb is that it takes about two gigabytes to store one hour of average video, the amount of video a DVD can hold depends on the amount of audio and the type of audio/video compression, as well as the associated audio tracks, menu complexity, and additional material. This means that a DVD-5, DVD-R, or DVD+R can hold up to about 130 minutes of high-quality digital video with standard bit-rate and a 48kHz audio stream. However, depending on the source material, a DVD-5 can hold up to 160 minutes at excellent quality. DVD-9 will hold about 4 hours of video, whereas a DVD-18 can hold about 8 hours of high-quality video.
Next week, Brian takes us through the planning stage.
For more info on Disc Makers, visit the company’s website.
OPTICAL DISC FUNDAMENTALS