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Making Sense of DVD
Chapter 1: Making Sense of DVD
So, what is DVD, and why is it interesting for desktop computer users? The letters in DVD can stand for "Digital Versatile Disc," or "Digital Video Disc", and versatile sums up DVD quite accurately. DVD is an optical disc format that was designed as a "convergence" media, bridging from computer to consumer, from data storage to multimedia playback. DVD spans the needs of Hollywood to computers, from the entertainment industry to the consumer electronics industry to computer manufacturers, and from consumers to business. And DVD has lived up to that original promise, first becoming a huge success as a product for watching movies, and now rolling into personal computers.
This chapter provides an overview of these different dimensions of DVD, and how it is becoming a useful and cost-effective tool for desktop video and data storage. It begins by discussing the motivation for the DVD format, and how it has exploded as a consumer product. It then explores DVD consumer formats and products for playing movies and even recording video. It then discusses the development of DVD on the desktop, including recordable formats, DVD burner drives, and authoring tools.
DVD has been a runaway success as a consumer product for watching movies, and now all the elements are in place for DVD on the desktop, with declining hardware and media prices and the availability of a wide variety of authoring tools.
See Appendix A, DVD Technical Summary, for a more in-depth discussion of the technical details of the DVD formats.
DVD can be thought of in several dimensions -- as a concept, a disc, the basis for a whole new category of consumer products, and a really interesting new capability for digital video on computers:
DVD is many things, and its scope is expanding:
First, DVD is an optical disc format.
The DVD format is the basis of several new lines of consumer electronics products.
DVD is also a computer data format.
Finally, DVD is the fulfillment of the promise of digital media on the desktop.
With a broad range of affordable DVD hardware burners and software-authoring tools, all these aspects combine to make DVD the last piece of the puzzle for digital video on computers. It is now feasible for individual users, from business professionals to consumer hobbyists, to process digital video directly from camcorder to DVD on the desktop. You can capture full-quality video from a DV camcorder on your computer, edit it with inexpensive tools, author video clips into professional-looking DVD productions including interactive menus, and then burn the productions to DVD discs -- all with full digital video and audio quality.
The DVD format has been primarily driven by the DVD Forum (www.dvdforum.com), which is an industry consortium of hardware manufacturers, software firms, and other users of DVD formats that has about 230 participating companies. In cooperation with Hollywood and computer industry organizations, the DVD Forum developed the initial standards for the DVD-Video digital video format for movies and the DVD-ROM format for computer data storage.
Hollywood's needs were for a movie experience with high-quality video supporting widescreen theatre aspect ratios, multichannel surround-sound audio, and content protection technology to prevent wholesale copying. The computer industry's needs were for a family of data storage and recording solutions, compatible for both data and video. The resulting DVD formats available today have fairly successfully satisfied these needs, although, as we will see, there is still too much confusion with competing formats for different applications.
In the past few years, the market has judged how successfully these goals for DVD have been achieved -- in a convincing fashion. The Consumer Electronics Association (CEA) has declared DVD to be "the fastest-selling consumer electronics product of all time," and DVD unit sales actually surpassed VCRs for the first time in September 2001.
Compared to VHS videotapes, movies on DVD discs are great for consumers for several reasons. DVD offers higher quality than VHS, of course, with higher-resolution video and a sharper picture, plus multichannel surround-sound audio with higher sampling rates, and more bits per sample. DVD also offers interactive access, with no more waiting to rewind or to fast-forward through a long tape, so you can jump directly to a chapter to pick up the story, or skip through the movie to see your favorite parts again.
Another important advantage of DVD over videotapes is that the discs can be played over and over again without degrading the quality. As parents with young children know, kids like to watch their favorite movie over and over again, but repeatedly playing a tape eventually starts to damage it. Videotapes will wear out as the tape head spins over the metallic surface of the tape. Over time and multiple viewings, the quality of the video signal will be reduced, and eventually will start having dropouts. With optical discs, such as DVD, however, there is no physical contact. Light from a laser is used to "read" pits in the surface of the disc to extract the digital data, so the data does not wear off, and the digital value is exactly the same each time you read it. In addition, videotapes degrade over time as the metallic particles flake off the tape, so videotapes can become unreadable in 15 years or less, depending on how carefully you store them. By comparison, different formats of CD and DVD discs are predicted to last more than 25 years, and may last up to 100 years.
At the same time, the digital DVD format fits well into similar trends with the adoption of digital (DV) camcorders and the growth of CD recording on personal computers. DV provides high-quality video input so desktop machines can become video workstations, and DVD goes beyond CDs to provide the capability to burn video productions to a removable disc, which can be played on both consumer and computer equipment.
Consumer DVD Movies: DVD-Video
The first consumer DVD products were DVD video players: set-top units that play DVD movies on your television. These products are based on the DVD-Video format, which was designed specifically for showing Hollywood movies that last more than two hours, with high-quality picture and sound:
Besides high-quality digital video and sound, and interactive menus, the DVD-Video format also provides advanced features to enhance your viewing experience with multiple tracks of video, audio, and subtitles.
For example, with multiple video tracks, you can watch a music performance, and switch between different camera angles to see individual performers and their different instruments.
With multiple audio tracks, you can watch the same movie dubbed in different languages, or listen to a director's commentary discussing how the movie was made.
And by combining multiple audio and subtitle tracks, you can practice your language skills by watching a movie dubbed in one language with the corresponding subtitles in the same or even a different language. Or you can turn a movie video into a karaoke experience, listening to the music while watching the subtitles to sing along with the lyrics.
Like audio CDs, DVD-Video movies are mastered; the disc contents are designed and authored at a production house, and the final disc image is then sent to a mastering facility so that the disc can be manufactured in large quantities. Unlike videotape, which needs to be recorded from beginning to end, CD and DVD discs can be manufactured -- essentially "stamped out" at the factory, which lowers the manufacturing cost.
The definition of the DVD-Video format includes both the physical structure of the disc, in terms of how the data is stored on it, and the logical organization of the audio and video material and control information found on the disc. A set-top DVD player product, or a computer DVD player software application, can then read the raw data off the DVD disc, search through the disc file structure to find the menus, jump to the chapter points, and play the audio and video streams from the disc.
Movies are converted to DVD by first digitizing the frames of film and associated channels of sound into digital format. The digital data is then compressed, typically into MPEG-2 video format and Dolby Digital (AC-3) or linear PCM audio format (see Chapter 2, Consumer DVD Players: DVD Video and Audio). The movie is then authored into DVD format by adding alternate tracks and subtitles; and then building in the navigational structure to the movie with chapters, menus, and links. Finally, all the DVD material, content and navigation, is combined and multiplexed together into the final DVD image, the exact data that will be written to the DVD. For making single copies of a DVD, the disc image can be burned to the DVD using a DVD recordable drive.
Consumer DVD on CD: Video CD / SVCD
Although DVD is thought of in the United States as the disc format for video, the CD format is also used for premastered material (especially CD Audio discs), and there is nothing preventing the distribution of video on CD as well. In fact, the Video CD (VCD) and Super Video CD (SVCD) formats have become very popular, especially in Asia, as an inexpensive medium for distributing shorts, such as music videos and even full-length movies . Many current set-top DVD players, and most DVD player software applications, will play discs in VCD format, and sometimes the SVCD format as well.
VCD uses the older MPEG-1 compression format, and has lower video resolution than DVD, but it can fit 74 minutes of "VHS-quality" video on a CD disc. The newer SVCD format uses the same MPEG-2 video compression format as DVD, although at a lower resolution, to fit around 35 minutes of "near-DVD" quality material on a CD. SVCD also supports interactive menu navigation like DVD. See the VCD Help website (www.vcdhelp.com) for more information on VCD and SVCD.
Another approach to sharing DVD content on CD discs is to simply do exactly that: Author DVD productions that are short enough to fit onto a CD (around 18 minutes at reasonable quality). These discs typically do not play on set-top DVD players, but they can be played on a computer with DVD player software. To make these discs more universally playable on any computer, some DVD authoring-software tools provide the option to include a DVD player software application on the CD disc.
DVD Video Camcorders and Recorders
DVD-Video can be used for more than just video playback. Just like CDs, DVD discs are available in both DVD-R recordable (write-one) and DVD-RW rerecordable (rewritable) formats. As a result, it is feasible to use DVD media to replace tape or hard disks in digital video recorders and videotape in digital camcorders.
DVD discs can be used in digital video recorders to provide digital recording on removable discs. You can use DVD recorders like a VCR to record TV shows. Unlike digital recorders that use built-in hard discs, DVD is a removable medium, so you do not have to worry about running out of disc space -- and you can save lots of shows to watch later. In addition, you can use a DVD recorder to transfer analog video sources directly to DVD. You can connect your 8mm camcorder or VHS VCR to convert old videotapes to DVD format so that they are saved in digital format (and are much more accessible and convenient to watch).
A roughly half-size mini DVD format (80mm versus 120mm for full-size DVD and CD discs) is being used for small devices, such as camcorders. Replacing tape with DVD provides the capability to easily review the material that you have recorded on your camcorder, as well as the instant gratification of popping the disc into a set-top DVD player to watch it on a TV.
Unfortunately, there are several different, and incompatible, recordable DVD formats currently available -- and some recordable formats may not play reliably on standard DVD-Video step-top players or computers. See Chapter 2 and Chapter 3, Consumer DVD Recorders: Recordable Formats for more on compatibility issues between different DVD formats.
Consumer DVD Music: DVD-Audio
More recently, the DVD Forum has defined a digital audio format, DVD-Audio, which was designed as a higher-quality upgrade from CDs. Like DVD-Video, the audio format supports multichannel surround sound, with higher quality than CD Audio. Some higher-end or "universal" DVD players now support playback of DVD-Audio format discs, but the market for audio-only DVD-Audio players is still developing.
The DVD-Audio format supports menus and navigation, such as DVD-Video. However, DVD-Audio is designed to support a wide range of player devices and capabilities. DVD-Audio discs can be used even in a simple CD-like car player that can simply jump from track to track, or on a smarter player with a text display that can display track information, or on a universal DVD player with a full graphical display on a TV screen with menus, slide-show graphics, and even video.
The DVD-Audio format was defined only recently (in 2000), so the market for the format is still developing. Many consumers are happy with CD audio, and even with compressed MP3 audio on their computers and portable audio players. Audiophiles are interested in CD-Audio for the higher quality and surround-sound experience, and the record companies like it because it provides the kind of content-protection and copy-prevention features that are totally missing from CD. The CD-Audio format is becoming more accessible as CD-Audio playback capability is built in to some set-top DVD players and DVD player software. However, the audiophile market is also fragmented by a competitive format: Super Audio CD (SACD), developed by Sony and Philips.
With the success of DVD as a consumer electronics product for watching movies, DVD-ROM drives for computers also have been catching on as standard equipment on new machines. DVD on computers provide a fun way to explore movies on your desktop, or, even better, to watch the movie of your choice on your laptop during a long airplane trip.
DVD player software applications can make the experience of watching a movie even more interesting because they provide more control than set-top players -- with features including direct access to the navigational structure of the disc, the capability to display multiple subtitles at the same time, fast scanning while still being able to listen to the audio, and Dolby Headphone processing to hear surround-sound effects from standard headphones.
Just this popularity of watching DVD movies has been enough to drive the sales of DVD drives on computers, becoming a common option on desktop and laptop computers, especially with new combination DVD-ROM readers and CD-R/RW read/write drives. However, the goal of being able to write DVDs on the desktop really became achievable only in 2001, with the breakout success of DVD-Video plus the convergence of stable formats, affordable burners, and usable software.
The basic DVD disc formats, and even the storage capacity, has taken several years to settle down. Even at the end of 2001, there was a surprising variety of formats for different uses (that is, write-once versus rewritable; data versus multimedia) and an ongoing marketing battle between two different formats designed for the same purposes. But the good news is that the market has settled on a standard basic capacity, and it is now feasible to burn DVD discs on your desktop and expect them to reliably play back on the vast majority of set-top DVD players.
The basic physical design decision for DVD discs was to use the same form factor as CD, a 12cm (120mm) diameter disc. Through advances in lasers and disc materials, however, DVD discs can cram more information onto the same surface area, or 4.7GB (billion bytes), versus 650 to 700 million bytes on a CD disc.
Unlike CDs, prerecorded DVD discs are available in double-sided formats, with twice the storage capacity (9.4GB) on a single disc. Some movies on DVD take advantage of this format to provide two copies of the same movie, widescreen on one side and cropped for television displays on the other; or to provide additional material, such as promotional trailers and "making of" documentaries, on the second side.
DVD discs also can be manufactured with two layers on the same side. By refocusing the laser beam, DVD players can "see through" the top layer of a dual-layer disc, to read the data on the second layer. Dual-layer discs (but single-sided) provide somewhat less than twice the storage capacity (8.5GB). Dual-layer discs are particularly useful for storing longer movies on a single side because the disc does not need to be turned over to access the additional capacity. However, there is a slight glitch when refocusing between layers, so the DVD needs to be designed to disguise the transition (for example, during a scene change in the movie with a fade to black).
In another example of fuzzy mathematics in the industry, single-sized 4.7GB discs are called "DVD-5," dual-layer 8.5GB discs are called "DVD-9," and double-sided 9.4GB discs are called "DVD-10," -- all through creative rounding up.
In addition, like CDs, DVD discs can be manufactured a smaller size. Smaller CD discs are particularly useful as computer-readable business cards and promotional items because they can contain contact information, and even product demos and brochures. The smaller DVD disc was designed for use in portable consumer electronics devices, such as digital camcorders. These "mini DVD" discs provide convenient and quick access for recording, viewing, and editing video right on the camcorder. They can then be removed and played back in a set-top DVD player, or read directly on a PC to view and edit. These smaller DVD discs are roughly half-size, or 8cm (80mm), and can store 1.4GB (or 2.8GB on both sides).
DVD Formats: Physical and Logical Discs
Defining a DVD disc format includes two aspects: the physical composition of the disc and the logical structure of the data stored on the disc. The physical disc format includes the surface material, the cylindrical groove structure and pits used to store data around the surface, and the type and wavelength of the laser used to read the data. The logical data format includes disc header information used to identify the type of disc, file structure, and data layout information used to find the different types of data on the disc (that is, audio and video, and chapter points), and the actual data formats (such as MPEG-2 video).
The physical disc format and surface composition also determine whether the disc can be modified to record new data, that is, by having the laser "burn" new data pits onto the disc, or even "melt" the material to erase data and then burn new information. The disc format may be prerecorded, manufactured with permanent read-only information; recordable, a blank surface than can be written to once; or rewritable, with a surface that can be written and then erased and rewritten.
As with CDs, various logical data formats can be stored on different physical disc formats. You can buy software on prerecorded CD-ROM data discs, or burn your own data files and directories to CD-R (Recordable, or write-one) or CD-RW (ReWritable, or re-recordable) physical discs. You can also buy music on a prerecorded CD, or burn your own music in CD-Audio logical format to CD-R or CD-RW discs.
The DVD Forum originally defined the basic formats for prerecorded discs, starting with DVD-Video for movies and DVD-ROM for computer data, and then recently adding DVD-Audio for music.
The DVD Forum also defined three recordable formats: DVD-R, DVD-RW, and DVD-RAM. The DVD-R/RW formats are recordable / write-once and rewritable / rerecordable formats, in the same spirit as the now-familiar CD-R/RW formats.
The DVD-RAM format, championed especially by Panasonic, was designed for data storage applications, with the capability to read and write randomly (instead of writing in long streams and bulk erasing), and with built-in error correction and defect management. Although DVD-RW discs can be overwritten 1000 times, DVD-RAM is designed to be written more than 100,000 times. For archival purposes, these kinds of DVD discs also can be expected to last 30 to 50 years.
In addition, the DVD-R format was split into two versions in early 2001 to help bring down prices for non-professional uses. The original format, now called DVD-R for Authoring, still provides the capability to make full DVD-Video discs, including the content protection and copy-protection features. Drives for professional use also continue to support the old 3.95GB authoring format as well. A new lower-cost format, called DVD-R for General, was introduced without the content-protection features, but still permitting desktop DVD authoring systems to create DVD-Video discs that play back on most set-top DVD players.
However, the DVD Forum is an industry coalition, not an international standards body, so the success of these formats depends on the support of its members in creating products, and ultimately on their acceptance in the professional and consumer markets.
DVD Forum Recordable Formats
Meanwhile, a second industry group, the DVD+RW Alliance (www.dvdrw.com), developed an alternate rewritable format, DVD+RW, ("plus RW"). The DVD+RW format was intended to provide much of the advantages of DVD-RW and RVD-RAM, and also be more compatible with existing set-top DVD players. After a long development period, products based on DVD+RW started to be released in the second half of 2001. A second related format, DVD+R, was also defined to compete with the DVD-R recordable format. DVD+RW is backed by a core group of companies, including Hewlett-Packard, Mitsubishi/Verbatim, Philips, Ricoh, Sony, and Yamaha; and has received support from Dell and Thomson/RCA.
Unfortunately, these competing formats will result in continued confusion in the marketplace and frustration with incompatibilities. The competition between them is based on technical, usability, and marketing factors, including competing claims of compatibility, consumer preferences for using rewritable media, and corporate partnerships to introduce broad ranges of products that support these formats. The result for consumers, we can hope, will include rapid reductions in hardware and media prices, and better compatibility with set-top players, if not between different PC drives. The results for the companies defining these formats will be better market share and a share of the income from the patent licensing pool.
DVD Formats: Compatibility
Given all these different formats and the ongoing marketing battle that may mean some of them may become obsolete, how can we choose which formats to use? Or is it better to delay getting into DVD in the hopes that things will get clearer in the near future?
The answer is actually pretty clear: If you are ready to use DVD on your desktop, then go ahead and get started now. You can use DVD as a large data disc to archive and share your computer files. You can use DVD to burn video productions that can be played on set-top players and PCs. You also can use DVD to create digital archives of your home recordings.
In particular, the DVD-R format is very well-established, so DVD-R discs that you burn at the desktop can be expected to play on almost all recent set-top DVD players and computer DVD-ROM drives. The DVD-RW format is physically similar, but some older drives were not designed to recognize the format, and may reject the discs. The new DVD+RW and DVD+R formats were designed to provide good compatibility, but they are still being established in the market, and will be verified over time. Finally, the DVD-RAM format is physically quite different from the DVD-R baseline, and can be used only in players and drives that are explicitly designed to support it.
But no matter the format, the DVD discs that you burn today will be just as compatible tomorrow, no matter what happens with the popularity of that specific medium for recording in the future. In fact, the whole competition over rewritable (RW) formats may become somewhat moot, at least for desktop uses. After all, write-once recordable (R) formats will always be popular for burning permanent copies of material to share and archive. In addition, as seen with the dramatic drop in CD-R media prices, if the price of recordable media is low enough, it is cheaper and more convenient to just use the same recordable media for everything, even if you expect that you could reuse the disc later.
However, with DVD, unlike CD, there is an additional large potential market for rewritable media in consumer electronics products, such as digital video recorders and digital camcorders. This is the key area of competition between the different rewritable formats, to provide a removable digital medium that provides the capability to quickly record, rerecord, edit, and play back video in recorders and camcorders. But the trade-off with these formats is that the discs they create may be less compatible with existing set-top players and PC drives.
DVD for Computers:
The Blu-Ray format replaces the red laser used for DVD with a shorter wavelength blue laser, squeezing the tracking pitch in half and permitting higher-density recording. With the increased capacity, Blu-Ray can continue to use the same MPEG-2 format used in DVD and high-definition television.
This group also aims to develop even large capacity formats, such as over 30BB on a single-sided disc and over 50-BB on a single-sided double-layer disc.
The desire for these new formats is being driven by the development of high-definition television around the world. The DVD Forum approach provides the capability to used more advanced compression to squeeze HD programs onto red-laser DVDs -- at least for pre-mastered videos. The Blu-Ray approach sticks with MPEG-2 to provide the possibility of real-time home recording of HD material, but this requires new technology and increased costs for new equipment.
Although the pace of new technology development, and the corresponding threat of quick obsolesce, can make buying into a new technology a sometimes uncomfortable prospect. The tremendous success of DVD says that it is here to stay, with its widespread adoption within the consumer electronics and computers industries, and across the consumer and professional markets.
Although set-top DVD players have already become a blowout success as a consumer electronics product, 2001 was a watershed year for DVD on the desktop, with the convergence of lower hardware prices and consumer-friendly DVD authoring tools. DVD became accessible as the final link for desktop digital video processing.
These days, on a standard desktop machine, you can now process full-quality video end to end: capture from DV camcorder, process with video editors and DVD authoring tools, and then burned to DVD disc, to play not only on other computers, but also on set-top DVD players.
As the result of the tremendous activity and competition in DVD software, you can get started with DVD authoring for under $150. Some of these all-in-one tools can work fine for both simple editing and automated DVD authoring, and the basic DVD tools are great for quickly banging out a collection of clips or a copy of a videotape onto DVD with minimal fuss. But as you get familiar with these tools, you will probably want to step up to some of the more professional dedicated DVD authoring tools, to give you more flexibility and control to make a more polished and customized presentation.