Copying rental dvd legal

Byline: Gary S. Hall

Technologies developed after Compact Disc standards were established make much higher data densities possible on standard 12 cm discs. New formats using smaller pit and track geometries as well as shorter-wavelength lasers allow several times the amount of data to be stored than was possible previously. That higher density in writing laser data opened the door for new standards, which in turn loosened the grip of CD patent holders Sony and Philips, allowing other companies to jump into the fray.

Toshiba became the leader in the formation of the DVD Forum (www.dvdforum.org), an association of more than 200 companies that guides the development of DVD formats. Not to be outdone, Sony and Philips have developed their own set of competing standards for audio, recordable DVD, and other emerging high-definition formats. The result is two groups of specifications for high-density media. The first, developed by the DVD Forum, consists of DVD-Video, DVD-Audio, DVD-R/RW, and DVD-RAM. The second, developed by Sony-Philips, consists of Super Audio CD (SACD), DVD+R/RW, and Blu-ray Disc. (For more details, see the sidebar "For Your Information.")

Officially speaking, the letters DVD no longer stand for anything. They were originally an acronym for Digital Video Disc, but because DVDs were to be used for audio and data as well as video, the meaning was changed to Digital Versatile Disc. When that term failed to catch on, the DVD Forum decided that DVD would simply stand for DVD.

Oddly, the DVD Forum neglected to lock up legal ownership of the term DVD, leaving the Sony-Philips group free to use it for its own format. DVD is now used for various sometimes-incompatible DVD Forum formats as well as for the Sony-Philips DVD+RW format. Although the latter is not endorsed by the DVD Forum, most writers and readers manufactured today support it. Fig. 1 shows the structure of the DVD Forum specifications.

READ-ONLY FORMATS

The DVD Forum specification for read-only DVD discs consists of four books. The first book consists of the physical- and file-system specifications known as DVD-ROM. The other books, called application layers, set the standards for DVD-Video, DVD-Audio, and DVD-ENAV (a recently-released enhanced DVD specification). Those specifications allow DVD discs to be played on commercial DVD players. The DVD-Video application layer, for example, defines a set of compatible media data types (primarily MPEG-2 video and Dolby AC-3 audio), a structure for onscreen menus, and an elaborate set of tables and indexes for navigating to the material on the disc. That application layer makes possible mass-market DVDVideo with its elaborate feature set and high degree of player compatibility.

The physical specifications of DVD-ROM cover things such as gross dimensions, track pitch, and pit size. The specification has options for one or two data layers and single- or double-sided discs, with capacities ranging from 4.7- to 14.7 GB. (The term layers here refers to physical layers on the disc, rather than layers as described in the previous paragraph.)

The file system describes the means of locating and accessing data using two forms of addressing. The first is based on sector offsets and is loaded when the disc spins up; the second, similar to the track addressing on audio CDs, is used by low-intelligence standalone players. The file system is also needed for computers to be able to read the discs, and the designers were careful to avoid the problems encountered with CD-ROM. The DVD file system is free of the major limitations in file naming and folder nesting of CDROM and is compatible with existing systems.

The DVD-ROM file system goes by the name ISO 9660/micro-UDF. The dual designation indicates that every DVD has two separate file systems. The data is not duplicated, but two sets of tables are provided to locate the data on the disc. A device reading the disc can use the set of file-system tables it understands. ISO 9660 is the CD standard and has backward compatibility. UDF stands for Universal Disc Format as defined by the Optical Storage Technology Association (OSTA). The "micro" designation indicates that DVD uses only part of UDF. Neither Windows nor Mac OS supported UDF initially, but now all major computer operating systems support it. Nevertheless, all DVD-format discs are required to support both ISO 9660 and micro-UDF.

DVD-Video is the textbook example of how to establish a format for market success. Technology companies and content providers were careful to define a robust feature set and to describe it in minute detail. That resulted in a remarkably smooth rollout, with few glitches in the design of players and production tools.

The feature set of DVD-Video is now well known, thanks to the many bonus-packed Hollywood DVD titles available for rental or purchase (see the table "DVD-Video Specifications"). For more detailed information on how DVD-Video works, check out the excellent summary at www.dvd-replica.com/DVD/index.php.

The development of DVD-Audio went far less smoothly than that of DVD-Video. A group of members of the DVD Forum interested in audio was relegated to work on the DVD-Audio format definition. Lacking the focus and motivation of the group that hammered out the video spec, the DVD-Audio group spent far too much time wrangling over competing agendas.

By the time a draft of the DVD-Audio spec was ready, downloading MP3 music files had rocked the music industry, and the DVD-Audio group had to rework its draft to beef up copy protection. When the full spec was finally released, interest at the major record labels had cooled, and titles (as well as the players to play them) were slow to arrive. In addition, consumers clearly valued the convenience and economy of CD over the superior fidelity of DVD. Furthermore, a competitor had emerged - Super Audio CD (SACD). (See the table "Feature Comparison of DVD-Audio and SACD" as well as the description of SACD later in this article.)

DVD RECORDABLE FORMATS

With recordable DVD, things get a bit confusing. The DVD Forum supports three variants of the DVD-R Write-Once format as well as two mutually incompatible rewritable formats, DVD-RW and DVD-RAM. To further confuse matters, the Sony-Philips rewritable disc format is named DVD+RW, even though it is not a DVD Forum format. I'll start with the write-once formats.

DVD Write-Once (DVD-R) is similar in principle and use to CD-R. Originally a professional medium for production houses and data-storage companies, DVD-R initially carried a high price tag - roughly $5,000 for the recorder and $20 or more for media. When the technology matured enough to lower prices, conflicting agendas emerged. The manufacturers of pro DVD-R drives and media were eager to keep their high profit margins, and copyright holders worried about rampant home copying of DVD-Video titles. That resulted in two DVD-R formats - one having two variants, and each differing in its compatibility with existing players.

The first DVD-R for Authoring format released to the professional market offered a capacity of 3.9 GB, compared with 4.7 GB for replicated discs. Although the capacity was less than they wanted, DVD-title producers were ready to pony up for any form of DVD-R they could get. When 4.7 GB recordable media became available, there were problems with player compatibility. As a result, both 3.9 GB and 4.7 GB versions of DVDR are used today.

DVD-R for Authoring still commands a premium price. It offers better player compatibility than formats available to the mass market, and it is free of copy restrictions. The default standard for holding capacity is 4.7 GB, but there are some older players that can't read the 4.7 GB discs. Media offering 3.9 GB remains available and is generally used for testing because it allows the latest features to be tested on the earliest DVD players. That is of particular importance for high-end Hollywood producers, who strive to obtain the broadest possible compatibility.

DVD-R for General has different reflectivity from DVD-R for Authoring and has reduced compatibility with older DVD players. When you record on a consumer-grade, write-once DVD, your discs should play on newer players but not necessarily on older ones.

DVD-R for General also uses the Serial Copy Management System (SCMS). With SCMS, a copy thus can be made of an original DVD, but during the copying process the DVD-R drive flips a bit in a special area of the disc. Trying to make a copy of the copy results in an error. Support of SCMS is mandated by the DVD Forum in all DVD-R drives that record to the General media.

DVD RERECORDABLE FORMATS