Chapter 2

DVD FORMAT SPECIFICATIONS

The DVD Forum has released separate books to document each of the following DVD specifications (listed with the current version at the time of this writing).

•   DVD-Video v1.11

•   DVD-ROM v1.02

•   DVD-Audio v1.2

•   DVD-R v2.0

•   DVD-RAM v2.1

•   DVD-RW v1.1

•   DVD-Video Recording v1.1

•   DVD Stream Recording v1.0

Each of the listed formats are “official” DVD formats, which means they have gone through a formal submission and review procedure and they have been approved by a vote of DVD Forum member companies. The submission, review, and approval process can take up to two years for a new DVD format. The DVD Forum is currently developing specification for advanced interactive content, also know as WebDVD, which defines an optional mechanism to include links between content stored on DVD-Video titles and content available on the Web. The decision to develop a WebDVD specification was made in May 2001, so we may not see a formal specification approved by the DVD Forum until the end of 2002, if ever.

Sony and Philips have proposed an alternative to the recordable DVD specification called DVD+RW, which was published in 1999 and revised in 2000. Sony and Philips has also proposed an alternative to the DVD-Audio specification that is called Super Audio CD (SACD), which was published in 1999. As shown in Figure 2.1, all of the DVD format books include a physical layer section, which defines the physical properties of the disc, and a file system layer section, which defines how data will be stored on the disc. The DVD-Video and DVD-Audio format books also include an application layer section, which defines how multimedia data will be formatted and stored on the disc and read back by DVD-Video and DVD-Audio players to create high quality home entertainment devices.

The physical layer section for the DVD-ROM, DVD-Video, and DVD-Audio formats are the same, and define the physical properties of a read-only DVD optical-disc. The physical layer section of the DVD-R write-once format and the DVD-RAM and DVD-RW read-write formats are different since these media types are physically different from the mass-produced DVD-ROM, DVD-Video, and DVD-Audio discs.

Each of the format books allows a micro-UDF file system to be used. Micro-UDF is a new optical disc file format specification developed by the Optical Disc Storage Association (OSTA) and is designed to allow optical discs to be compatible with all major operating system software (Windows, Mac OS, Unix, Linux, etc.). The DVD-ROM, DVD-Video, and DVD-Audio format books also allow for a standard ISO 9660 file system to be used in addition to UDF. The DVD-Video and DVD-Audio format books include an application layer section that defines how video, audio, graphic, and textual information will be digitized, compressed, and stored onto the DVD disc, and how the various interactive features of the DVD-Video and DVD-Audio formats will be implemented and used.

A copy of the DVD format books can be purchased for $5,000 from:

Figure 2.1  DVD Format Books Published by the DVD Forum

A signed confidentiality agreement and full payment must be received prior to shipment of the DVD format books. It is generally not necessary for DVD authoring or production companies to purchase a copy of the DVD format books. While the format books provide all of the low level details required to completely understand and implement the DVD-Video specification, they are typically only required for companies that are developing DVD-Video players, DVD-Video decoders, or DVD-Video authoring tools. Some advanced DVD-Video title developers may find access to these format books can be beneficial in understanding nuances of the DVD-Video format, but in general this is not required.

DVD Forum

The DVD Forum is an organization whose goal is to promote broad acceptance of DVD products on a worldwide basis. The DVD Forum has targeted the entertainment, consumer electronics, and information technology industries as potential users of DVD technology. The DVD Forum performs the following functions.

•   Defines the requirements and specifications for all DVD formats including DVD-Audio, DVD-R, DVD-RAM, DVD-ROM, DVD-RW, and DVD-Video

•   Publishes the various DVD format books

•   Licenses the DVD Format and DVD Logo, through the DVD FLLC organization

•   Administers the DVD Verification Labs throughout the world

•   Holds worldwide DVD conferences, promotes DVD through public relations activities, and maintains the DVD Forum web site (http://www.dvdforum.org)

The DVD Forum currently has 64 Principal Members and 235 Associate Members. Principal Members are allowed to participate in defining the DVD formats, and can vote at the DVD Forum general meetings. The annual fee to become a Principal Member of the DVD Forum is approximately $8,000 (1,000,000 Yen). Associate Members are provided access to the DVD Forum Technical Working Group reports. The annual fee to become an Associate Member of the DVD Forum is approximately $2,500 (300,000 Yen). Current members of the DVD Forum Steering Committee include Hitachi, IBM, Intel, ITRI, JVC, LG, Matsushita, Mitsubishi, NEC, Philips, Pioneer, Samsung, Sharp, Sony, Thomson, Time Warner, and Toshiba.

The DVD Forum currently has eight Technical Working Groups.

1.   DVD-Video and Video Recording

2.   DVD-ROM

3.   File Format

4.   DVD-Audio

5.   Rewriteable (DVD-RAM)

6.   Write-Once (DVD-R) and Re-Recordable (DVD-RW)

7.   Copy Protection

8.   Pro-Use Applications

Figure 2.2  DVD Single Layer and Dual Layer Disc Construction Diagram

DVD Physical Specifications

Two of the primary technical goals of DVD are to provide both higher capacity and higher throughput than CD-ROM technology offers. All DVD formats and playback devices support a minimum throughput rate that is at least nine times faster than a conventional CDROM, and many DVD playback devices support even higher transfer rates. The DVD-ROM, DVD-Video, and DVD-Audio formats have storage capacities between 4.7 and 17.0 billion bytes. The variation in total storage capacity depends on the use of up to two data storage layers on each side of a DVD disc.

The DVD physical specification provides for up to four different data recording layers and two different sizes (12cm and 8cm in diameter). A single-layer, single-sided disc is referred to as a DVD-5; a dual-layer, single-sided disc is a DVD-9; a single-layer, dual-sided disc is a DVD-10; and a dual-layer, dual-sided disc is a DVD-18. It is technically possible to have a DVD disc that uses three recording layers, two on one side and one on the other. This is called a DVD-14, but is not very common.

Figure 2.2 shows how a single-layer and dual-layer DVD disc are constructed. Both single-layer and dual-layer discs are made from two distinct pieces of molded plastic that are bonded, or glued, together. For a DVD-5 disc only one recording layer is used so a reflective material is added to the middle of the disc. Then the laser can read the data stored just before the reflective material. For a dual-layer disc two data layers are recorded and separated by a semitransmissive layer. If the laser is focused on the data recorded on Layer 0, which is on the bottom of the disc, then it is reflected to the optical sensor. If the laser is focused in the data recorded on Layer 1, which in on the top part of the disc, then the semitransmissive material allows the laser to pass through and read the data on the top layer. The semitransmissive material used on most dual layer DVD discs is gold.

DVD increases capacity through the use of multiple layers and specialized lasers, which use a shorter wavelength than traditional CD-ROM devices. This means that the pits and tracks used to store data on a DVD disc can be much smaller than those used on a CD-ROM.

A traditional CD-ROM uses pits that are at least 0.83 microns long, and has tracks that are spaced 1.6 microns apart. A DVD disc uses pits that are at least 0.4 microns long, and tracks that are spaced 0.74 microns apart. The pits and tracks used in DVD are less than half the size of the pits and tracks used on CD-ROM discs.

The use of smaller pits and more closely spaced tracks on a DVD optical disc increase the total storage capacity by over 700 percent compared to a traditional CD-ROM. Figure 2.3 shows the difference between the pits and track spacing on a CD-ROM and DVD-ROM, DVD-Video, DVD-Audio, DVD-R, and DVD-RW discs.

Figure 2.3  Comparison of DVD-ROM Vs CD-ROM Pit and Track Sizes

Using multiple layers and multiple sides for data storage has increased total capacity to a maximum of 15.9 Gb on a DVD optical disc compared to just 650 Mb on a standard CDROM — an increase of more than 25 times the capacity.

Table 2.1 provides the relevant physical properties and storage capacities for each type of DVD disc. The DVD format books refer to the storage capacity of each type of DVD disc as Gbytes, but this term has a different meaning than the classic definition for computer Gb. In the field of computer science a byte is defined as 8 bits of data, Kb as 1,024 bytes, Mb as 1,024 Kb, and Gb is 1,024 Mb. In the DVD format books a GByte is simply defined as 1 billion bytes. This is about 7.3 percent less than a computer Gb, which is actually 1,073,741,824 bytes. When working with DVD disc storage capacities it is important to keep this difference in mind.

It is also important to note that the capacity of a dual layer (DVD-9) disc is not simply double the capacity of a single layer (DVD-5) disc. Dual layer discs have a slightly larger mark pitch than single layer discs do, so a dual layer disc can only hold about 82 percent more than a single layer disc. Table 2.2 shows some of the common physical properties of DVD discs.

Table 2.1 DVD Storage Capacity Chart

Table 2.2 DVD Physical Parameter Chart

DVD File System Specifications

The DVD-Video format book requires the use of a general purpose volume and file layout structure so that DVD discs can be read by a variety of consumer and computer electronics devices, regardless of the specific processor or operating system used to access the disc. The DVD-Video format book requires the use of either the ISO-9660 or Micro-UDF (Universal Disc Format) file formats for storing data on a DVD disc. The ISO-9660 format has been in use for a number of years, and most CD-ROM discs that are cross-platform compatible use this format. DVD currently implements a hybrid approach, called UDF-Bridge, that provides both the newer UDF system as well as the older ISO-9660 system used by the CD-ROM format. This allows DVD discs to be used with computer operating systems that do not have any provision for UDF support.

DVD-Video requires that data stored on the disc follow the volume structure shown in Figure 2.4. Lead-in and lead-out areas are provided at the start and end of the disc to facilitate synchronization of DVD players with the data stored on the disc. An ISO-9660 and Micro-UDF file format is used to store all data. Video, audio, subpicture, menu, and still image data elements are stored in the DVD-Video zone area of the disc. The data is logically organized into the Video Manager area, which acts as the table of contents for the disc, and up to 99 Video Title Set areas, which hold individual programs, or collections of multimedia content.

All DVD discs should be mastered to include all required data as specified by ISO 13346 and UDF. This allows the playback of DVD discs on standard computer systems that support either the ISO 13346 or UDF formats. The ISO is the International Standards Organization that sets worldwide standards for a wide variety of industries, including personal computers and consumer electronics devices. Examples of such required data include the time, date, permission bits, and a free space map (indicating no free space if ROM media). While DVD player implementations may ignore these fields, a UDF computer system implementation will not. The UDF format has many features and can be complicated, however much of the information can be ignored in a dedicated DVD player environment. Due to limited computing resources within a DVD consumer player, only a subset of the UDF format is used for storing data on the DVD disc. The following restrictions apply to using the UDF format for DVDVideo discs.

Figure 2.4  DVD-Video Volume Layout Hierarchy

•   DVD-Video files should be stored in a subdirectory directly under the root directory. The directory name should be Video_TS.

•   DVD-Video file names should consist of the characters A-Z (upper case), 0-9 (digits), _ (underscore), and . (period). Not more than one . should be used in a file name.

•   Maximum compatibility will be ensured if the DVD-Video file names consist of no more than eight characters, optionally followed by a ., optionally followed by no more than three characters.

•   There should not be any files in the DVD-Video directory that differ only by case (i.e., Movie and movie cannot coexist).

•   DVD-Video authoring systems should constrain individual files to less than 1 Gb.

All these constraints apply only to the directory and files to which the DVD-Video player needs access. There may be other files and directories on the DVD disc that are not intended for the DVD-Video player and do not meet the listed constraints. Files outside the Video_TS directory, as well as files in the root directory, are ignored by the DVD player.

Copies of the UDF Specification can be obtained from:

Most DVD authors and producers will not need to know the details of how the volume and file information is stored on a DVD disc. The authoring tools you’ll use to create the DVD disc image will handle all the nuances of creating a valid DVD volume and file structure. However it is helpful if DVD authors and producers understand the file naming conventions used on DVD discs, and what each file is supposed to do.

All the files required for a DVD-Video title are stored in a directory called Video_TS in the root of the DVD disc volume. Within this directory there will be a number of files with three different types of extensions. Figure 2.5 shows the directory and file structure of the StarGaze disc.

Figure 2.5  DVD-Video File Structure

Files that end with the .ifo extension are information files that describe the content stored in the DVD-Video zone of the disc and how that content can be accessed directly. Files that end with the .bup extension are backup copies of the .ifo files with the same name. Files that end in the .vob extension are Video Objects that contain all the still images, video streams, audio streams, subtitle streams, and menus that are included on the disc.

DVD-Video

DVD-Video is a read-only optical-disc format that can be used for the interactive playback of high quality video, audio, and graphics content. The DVD-Video format allows consumers to playback full-length motion pictures as well as interactive games with higher quality than traditional VHS, SVHS, CD-i, and Laserdisc playback systems. The DVD-Video format can deliver full screen, full motion video at a resolution of 720 480 pixels per frame and a frame rate of 30 frames per second for NTSC countries, or 720 576 pixels per frame and a frame rate of 25 frames per second for PAL countries. Video quality delivered by a DVD-Video player has the potential to be as good as the original broadcast source tape.

The DVD-Video format supports extremely high quality audio using either Dolby Digital 5.1 channel surround-sound, linear PCM encoded audio, DTS surround sound audio, or Sony SDDS surround sound audio. Each of these digital audio formats provides significantly better quality than traditional Audio-CD devices. The DVD-Video format also provides the capability of storing up to eight different audio tracks that are all synchronized to the digital video stream.

The DVD-Video format supports up to 32 subpicture streams used for subtitles, closed captioning, graphical overlays, and even simple animations. Each subpicture stream is synchronized to the video and audio streams so that a wide variety of multimedia elements (video, audio, graphics, text, and animation) can be delivered to the user in a coherent fashion. The DVD-Video format can also deliver high quality still images that can be displayed for a fixed period of time, or until a user input is received.

The DVD-Video format supports a wide range of functions that enable the user to control and interact with the DVD-Video title. Simple functions such as start, stop, pause, fast forward, and reverse are provided so the user can control the playback of a title in a manner similar to a VHS, SVHS, or Laserdisc system. In addition to these simple interactive features, DVD-Video provides random access to all of the data on the disc, allowing the user to jump to any portion of the title in less than one second. Finally the DVD-Video format provides high-level interactive functions that allow the development of titles that ask the user to respond to questions, or to provide interactive menus to determine how the user wishes to view the title.

Video, audio, subpicture, still image, and control data are all multiplexed together within a DVD-Video title to form a single bit stream that can be decoded by a DVD-Video player in a manner that provides seamless transitions between different video scenes, language tracks, or subpicture streams. DVD-Video data has the following logical structure, as shown in Figure 2.6.

Figure 2.6  DVD-Video Logical Hierarchy

Title The Title area provides the ability to have up to 99 titles or episodes on a single disc. Titles can consist of a single program chain or multiple program chains. A title is typically used to store an entire movie or any items of content that can stand on their own.

Program Chain A collection of programs that are logically grouped together based on the content. Generally a movie is stored in a single program chain, while different episodes of a television series would be stored in separate program chains.

Part_of_Title Links to one or more programs. Part_of_Title can be used to support different versions of the title. For example if you developed a DVD for a movie that had several different endings, you would create a Part_of_Title for each unique ending. The Part_of_Title would call out the specific programs used in each variation of playback.

Program A collection of cells that are logically grouped together based on the content. Programs are usually used to identify different chapters within a movie.

Cell A collection of video or audio data packets that are logically grouped together based on the content. Cells are usually used to identify different scenes within a chapter.

VOBU Video Object Unit that is one or more MPEG Group of Pictures (GOP). A VOBU can be between 0.4 and 1.2 seconds long.

Group Of Pictures (GOP) The smallest granularity of random access to video data on the disc. A GOP typically includes compressed video data from 15 sequential frames of NTSC video, or 12 frames of PAL video.

Packet DVD-Video packets are 2048 bytes large and include only one type of data (video, audio, etc.). A packet is essentially equivalent to a single sector of data on the disc.

Navigation Packet (NAV) Contains optional commands that define the playback behavior of a cell. Navigation packs are used to control playback of the content at a very detailed level, for example you could use a navigation pack to skip over a specific Cell if it had a parental rating level higher than the player was set up to play.

DVD-Video can achieve the lofty goal of providing significantly better quality and more features than conventional VHS, SVHS, or Laserdisc players because it utilizes the latest digital techniques for encoding video, audio, still images, sub-picture information, and animation data.

MPEG Video

The DVD-Video format requires that video data be compressed in either the MPEG-1 or MPEG-2 formats. A compressed format is used to reduce the total data storage requirements for the video elements to a manageable level. “Broadcast” or “CCIR-601” quality video requires approximately 21 Mbytes/second of storage space and throughput. This means that a DVD-5 disc (4.37 GBytes) could hold only about 3.7 minutes of uncompressed, or raw, video.

MPEG-1 compressed video has a resolution of 352 240 pixels per frame and a frame rate of 30 non-interlaced frames per second (for NTSC countries). Most MPEG-1 files are compressed at a constant bit rate of approximately 1.4 Mbits/Second, which is consistent with the recommendations of the Video-CD standard. MPEG-1 compressed video provides quality roughly comparable to VHS tape, and if higher data rates are used the quality can approach SVHS tape. A standard DVD-5 (4.3 Gb) disc can hold approximately 7.5 hours of MPEG-1 video compressed at standard Video-CD rates. Video CD is an extremely popular format in Asia, but has never caught on in either the US or Europe since both areas had large installed bases of VHS players when Video CD first became available. Many DVD-Video players support the Video CD format, and some of the first titles released for DVD players were actually Video CD discs with MPEG-1 data. Despite Video CD’s popularity in Asia, the vast majority of DVD-Video titles have been published using MPEG-2 compressed video in order to provide better overall video quality.

MPEG-2 compressed video has a resolution of 720 480 pixels per frame and a frame rate of 30 frames per second for NTSC countries, or a resolution of 720 576 pixels per frame and a frame rate of 25 frames per second for PAL countries. MPEG-2 files can be created using a constant-bit-rate encoding process or a variable-bit-rate encoding process. If a constant-bit-rate encoding process is used a bit rate of approximately 6 Mbits/Sec or higher is required to provide compressed video that is as good as the original CCIR-601 source. If a variable-bit-rate encoding process is used, an average bit rate of less than 4.0 Mbits/Sec can be used to generate compressed video that looks nearly as good as the original CCIR-601 source.

Figure 2.7 shows the steps required to generate an MPEG-2 compressed digital video file. CCIR-601 component video is fed into a series of pre-filters and temporal and spatial scaling equipment to generate a high quality component digital video signal. The digital signal is then converted from RGB component format into the Y/Cr/Cb component format. Each frame of digital video is compressed using a Discrete Cosine Transform algorithm that removes redundant data (Intraframe Compression). Next each frame is compared to previous and future frames to eliminate redundant data between frames (Interframe Compression). Finally the compressed video data is formatted to comply with the MPEG-2 file format standards.

Figure 2.7  MPEG Video Compression Process Block Diagram

An MPEG-2 bit stream, as shown in Figure 2.8, is composed of a sequence of Slices, Pictures, and Group Of Pictures. An MPEG-2 Picture corresponds to a single full resolution frame, with two Slices that correspond to each field of the interlaced frame. There are three types of encoded frames in MPEG-2. An I frame includes all of the information required to fully reconstruct the source frame. Subsequent Pictures within the Group Of Pictures will be P or B frames. P and B frames are predictive frames, which means they only store the changes from the previous or next frame. A Group Of Pictures is a sequence of compressed frames that starts with a Picture that is an MPEG-2 I frame. The DVD-Video format book requires that the MPEG-2 compressed digital video stream include no more than 18 Pictures in each Group Of Pictures. The number of Pictures in a Group Of Pictures is also called the GOP size. The DVD-Video format book also requires that the MPEG-2 video data be multiplexed with any associated audio, sub-picture, still image, and control data.

Figure 2.8  MPEG-2 Bit Stream Syntax

When variable bit rate encoding is used, the actual number of bits dedicated to the MPEG encoding process is varied depending on the content of the video stream. If the video content is a scene of someone speaking, with a relatively static background, then fewer bits can be used to accurately describe the static scene. If the video content is a high action scene with both foreground and background motion, or a scene with a lot of fine detail, a higher bit rate must be used to avoid introducing digital artifacts into the compressed digital video file.

Lossy digital video compression techniques, including MPEG-1 and MPEG-2, can create digital artifacts during the compression process. Digital artifacts can include Color Distortion, Color Bleeding, Hue and Tint Degradation, Motion Degradation, Noise Pumping, Frame Duplication, Frame Drops, Aliasing, Blocking, Fringing, and Ringing. The most common digital artifacts generated in MPEG compressed video streams are Blocking, Color Bleeding, and Fringing. Blocking is the presence of 8 8 pixel pattern blocks in the compressed video stream that were not part of the original source. Blocking is caused by the use of the Discrete Cosine Transform algorithm, which operates on an 8 8 pixel block. Color Bleeding occurs when colors from one area of a frame migrate into neighboring areas of the same frame. Color Bleeding occurs more often with “hot” colors such as red, yellow or orange. Ringing is the presence of a blurring, or out of focus effect around the edges of an object that is moving from frame to frame. Ringing occurs more often when there is a large amount of motion between frames of the video.

Digital video artifacts can be eliminated using a variety of techniques. Most artifacts can be removed by increasing the average bit rate used to compress the content. Filtering the input video stream to eliminate high frequency noise is also a common technique for reducing artifacts. Artifacts that occur in only a single frame of the digital video can be removed by touching-up the pixels that have been distorted, although this is a very labor-intensive process.

Multiple Screen Aspect Ratios

In the early days of film all movies were shot in a 4:3 aspect ratio. As movie theatres got larger filmmakers started shooting in wide screen formats so that the movie would fill the available screen size on the stage. When television came along it was decided that all video displayed on a television would have a 4:3 aspect ratio. Today we have a number of different aspect ratios in used by filmmakers and television producers, and all of this content may eventually be transferred to DVD. Thus the DVD-Video format needs a method of handling content with different aspect ratios.

The DVD-Video Format supports the use of normal, pan-scan and letterbox formats when displayed on either 4:3 standard or 16:9 wide-screen monitors. Figure 2.9 shows how a video image created for 4:3 or 16:9 displays will look when the normal, pan-scan, letterbox, and 16:9 formats are used. Obviously a video that has been generated in the 4:3 format will look correct on a standard 4:3 monitor, and a video that has been generated in the 16:9 format will look correct on a wide-screen monitor. However, when a 4:3 formatted video is displayed on a 16:9 monitor, or a 16:9 formatted video is displayed on a 4:3 monitor, the original image will not be reproduced accurately. There are several techniques used to avoid this problem including Pan/Scan to convert a 16:9 image to a 4:3 resolution and letterboxing to display a 16:9 image on a 4:3 display in its entirety.

Figure 2.9  DVD-Video Multiple Aspect Ratio Comparison (See color insert for color version of this figure.)

Multiple Camera Angles

Up to nine different camera angles are supported by the DVD-Video format. The viewer can seamlessly switch between viewing angles by using the “Angle” button on the DVD-Video player’s remote control. There are some restrictions on the use of multiple video angles, such as the length and average bit rate of each unique video angle must be approximately the same. Multiple camera angles can be used to provide different perspectives, or to provide alternative content. For example multiple camera angles have been used to provide both a finished animated video sequence as well as the wire frame animation so the viewer can understand the process used to create the video sequence, or for a sporting event where one camera angle could provide a wide angle view of the entire playing field, another could have a close up view following the soccer ball, while a third angle could provide a close up of the goal keeper.

High Quality, Multiple Channel Audio

The DVD-Video Format provides for the incorporation of high-quality, multiple channel audio using one of the following formats: Dolby Digital Stereo, Dolby Digital 5.1 Channel Surround Sound, Linear PCM Stereo, MPEG-2 Stereo, MPEG-2 Surround Sound, DTS Surround Sound and Sony SDDS Surround Sound. The Dolby Digital and Linear PCM formats are required to be supported by DVD-Video players, with MPEG-2 (stereo and surround), DTS and SDDS audio optional. The vast majority of DVD-Video players throughout the world support Linear PCM and Dolby Digital audio. Many players support the DTS audio format as well. MPEG-2 audio is supported on some European model DVD-Video players, but in general it is not supported on US player models. Most of the DVD-Video players on the market today, and sold over the past five years will not support playback of DVD-Audio discs, which generally included linear PCM or Meridian Lossless Packing (MLP) data. Consumers will need to purchase a DVD-Audio player or upgrade their DVD-Video player to a Universal player in order to play back DVD-Audio titles.

DVD-Video supports up to eight simultaneous tracks for audio, in any of the formats listed above. Each audio track is multiplexed into the overall DVD-Video bit stream so that they are synchronized with the video stream. DVD-Video players are designed so that the user can switch between the available audio tracks at any time during playback of the title. Switching audio tracks is a seamless operation that requires less than a second to complete. Video playback will continue without interruption during an audio track change.

Most DVD-Video titles include Dolby Digital stereo, or Dolby Digital 5.1 Channel Surround Sound audio tracks. Dolby Digital is a perceptual digital audio coding technique that has been used in movie theaters since 1992. Dolby Digital divides the audio spectrum of each channel into narrow frequency bands of different sizes optimized with respect to the frequency selectivity of human hearing. This makes it possible to sharply filter coding noise so that it is forced to stay very close in frequency to the frequency components of the audio signal being coded. Reducing or eliminating coding noise wherever there are no audio signals to mask it can subjectively preserve the sound quality of the original signal.

In Dolby Digital, bits are distributed among the filter bands as needed by the particular frequency spectrum or dynamic nature of the program. A built-in model of auditory masking allows the coder to alter its frequency selectivity (as well as time resolution) to make sure that a sufficient number of bits are used to describe the audio signal in each band, thus ensuring noise is fully masked. Dolby Digital also decides how the bits are distributed among the various channels from a common bit pool. This technique allows channels with greater frequency content to demand more data than sparsely occupied channels, for example, or strong sounds in one channel to provide masking for noise in other channels.

Dolby Digital can process at least 20-bit dynamic range digital audio signals over a frequency range from 20 Hz to 20kHz x 0.5dB (-3dB at 3Hz and 20.3 kHz). The bass effects channel covers 20 to 120 Hz x0.5 dB (-3 dB at 3 and 121 Hz). For DVD-Video applications a sampling rate of 48 kHz is used. Data rates range from as low as 32 kb/s for a single mono channel to as high as 640 kb/s, thereby covering a wide range of requirements. Typical applications include 448 kb/s for 5.1-channel Dolby Digital consumer format, and 192 kb/s for two-channel audio distribution.

As shown in Figure 2.10, Dolby Digital 5.1 Channel Surround Sound delivers six totally separate (discrete) channels of sound including Left, Center and Right channels across the front of the room, and left surround and right surround channels located behind or to the side of the listener, for more precise localization of sounds. All five main channels are full range (3 Hz to 20,000 Hz) and a subwoofer can be added to each channel, if desired.

Figure 2.10  5.1 Channel Surround Sound Speaker Placement

The sixth channel, called the Low Frequency Effects Channel, will, at times, contain additional bass information to maximize the impact of scenes such as explosions, crashes, etc. Because this channel has only a limited frequency response (3 Hz to 120 Hz), it is sometimes referred to as the “.1” channel. When added to the 5 full range channels, the Dolby Digital system is usually referred to as having “5.1” channels.

For Linear PCM and DTS audio the sixth channel includes the same frequency response as the other five channels so it is capable of carrying sound other than low frequency effects. Very few DVD-Video titles have been developed using six channel Linear PCM audio as it uses over 60% of the available DVD-Video bit rate for just a single track of audio, leaving an inadequate amount of bandwidth for video, subpictures or additional audio tracks. DVDVideo titles with six channel DTS audio tracks are quite common, although in the vast majority of cases the sixth channel is used to carry low frequency effects sound.

Multiple Subpicture Streams

The DVD-Video format supports up to thirty-two (32) simultaneous subpicture streams for use as subtitles, closed captions, graphical overlays or simple animation. Each subpicture stream is multiplexed into the overall DVD-Video bit stream so that they are synchronized with the video and audio data. Subpicture streams are stored as Run Length Coded Bit Maps with 2 bits allocated per pixel of data. For countries that use the NTSC television standard Sub-pictures have a resolution of 720 478 pixels, while in countries using the PAL standard have Sub-pictures with a resolution of 720 573 pixels. A subpicture is created using only four colors from a 16-color palette, and four unique contrast levels. Special effects such as scroll up, scroll down, fade in, and fade out can be applied over a sequence of video frames. The sub-picture color palette can be changed for each program chain.

The use of subpicture streams on DVD-Video titles is quite common. Subpictures are routinely used for foreign language subtitles, closed caption, and captions for the hearing impaired. Innovative uses of subpictures have included an animated director commentary where the silhouette of the directors was displayed in the bottom corner of the video display while the director’s commentary is played on a supplemental audio track. Subpicture streams have even been used to provide alien language translations in the Klingon language.

High Quality Still Images

The DVD-Video format supports the use of high quality still images that can be displayed for a fixed length of time, or until a defined user input is received. Still images are stored as either MPEG-1 or MPEG-2 I frames (full reference frames). When a still image is encountered in the DVD-Video bit stream the video and sub-picture streams are frozen, and the audio is muted. MPEG-1 still images have a resolution of 352 240 pixels for NTSC, and 352 288 for PAL. MPEG-2 still images have a resolution of 720 480 pixels for NTSC, and 720 576 for PAL. The size of each compressed still image is dependent on its content, and the degree of compression that can be applied without creating digital artifacts.

Navigation & Search Functions

DVD-Video supports a wide variety of navigation and search functions that allow users to control and interact with titles. User controlled search functions include:

Title Search The user can select a specific title from the list of available titles on the DVDVideo disc.

Part_of_Title Search The user can select a specific chapter available on the DVD-Video disk.

Program Search The user can select a specific scene within a program chain.

Time Search User can select a specific time code location within a program chain.

Scan The user can scan either forward or backward in time through the current title.

GoUp The user can jump to the start of the next program chain. Many DVD-Video players include this feature as the Return button on the remote control.

The DVD-Video title author can disable the Part_of_Title, Program, Time, Scan, and GoUp search functions.

Navigation commands allow the DVD-Video author to control the playback of the Title, Part_of_Title, or Program that has been selected by the user. Navigation commands can be used in four different command areas within a DVD-Video title. These are the Button, Cell, Pre, and Post command areas. Navigation commands are all eight bytes, and include Single Instruction Commands and Composite Instruction Commands. Single Instruction Commands include a single instruction while Composite Instruction Commands can include two or three instructions. There are six different types of Navigation Commands.

GoTo Branch between commands

Link Transfer between the same domain

Jump Transfer between different domains

Compare Recognition of parameter value

SetSystem DVD-Video player system settings

Set: Calculate DVD-Video general parameter values

Additional details on the use of Navigation Commands are provided in Chapter 6, Section “Professional DVD Authoring” on page 183.

System Parameter Registers (SPRM)

There are 24 unique player SPRM, as shown in Table 2.3 (page 26). SPRMs store a fixed length, 16-bit numerical value, and are used to keep track of user preferences as well as player capabilities information. For example if the viewer prefers to see French language subtitles if they are available, then SPRM 17 and 18 will be set up to store that information. Some SPRM registers are set up by the player manufacturer and others are configured by the viewer when the use the DVD-Video players on-screen configuration menus. All SPRM registers can be read during playback of a DVD-Video title using standard navigation commands. DVDVideo titles can be designed to read the SPRM registers and take appropriate action based on the user preferences and player capabilities.

There are also 16 general parameter registers (GPRM) that can be used by the DVD-Video title author to control playback of the title. GPRMs can be used to stored fixed length, 16-bit numerical values, which are treated as unsigned integers. There are two modes of operation for GPRMs, register mode and counter mode. In counter mode the value of a GPRM is automatically increased by one every second. All GPRMs are set to zero and placed in register mode when a DVD-Video title is first started. Chapter 6 provides an in-depth discussion on how to use SPRM and GPRM registers to create highly complex or interactive DVD-Video titles.

Regional Coding

In order to gain the support of the major motion picture studios, the DVD Forum had to modify the original DVD-Video specification to include Region Coding. Region Coding is designed to allow the major motion picture studios to control the release of their titles throughout the world. The world was broken up into eight regions and if a studio only wanted to release a title in the United States, then they would create a DVD-Video title where only Region 1 (North America) playback was enabled. Consumers in other regions of the world would be unable to play back the title since their player’s internal region code would not match the titles region code.

Table 2.3 DVD-Video SPRM Descriptions
# System Parameter Description	# System Parameter Description
0 Menu Description Language Code	12 Country Code for Parental Management
1 Audio Stream Number	13 Parental Level
2 Sub-picture Stream Number	14 Player Configuration for Video
3 Angle Number	15 Player Configuration for Audio
4 Title Number	16 Initial Language Code for Audio
5 VTS Title Number	17 Initial Language Extension for Sub-pictures
6 Title PGC Number	18 Initial Language Extension for Audio
7 Part_of_Title Number for one sequential_PGC_Title	19 Initial Language Extension for Sub-picture
8 Highlighted Button Number	20 Player Region Code Mask
9 Navigation Timer	21 Reserved
10 Title PGC Number for Navigation Timer	22 Reserved
11 Audio Mixing Mode for Karaoke	23 Reserved

When a DVD title is manufactured one or more regional codes can be stored on the disc. Similarly, when DVD players and DVD-ROM drives are manufactured, a regional code is stored within the player hardware. The DVD player performs a comparison of its own internal regional code with the code stored on a DVD disc loaded into the player. If the regional codes match, then the DVD player will display the menu of available titles, or will start playing the default title. If the regional codes do not match the DVD player will not provide the user with access to the titles stored on the disc. Regional coding methods have been used for many years by the movie industry to control distribution of their content throughout the world.

For DVD players and titles there are 7 regions that have been defined. A region number superimposed on a world globe is used to identify players and discs. If a disc plays in more than one region it will have more than one number on the globe. DVD-Video regional codes are defined as follows:

1.   North America

2.   Japan, Europe, Middle East, South Africa

3.   Southeast Asia (including Hong Kong)

4.   Australia, New Zealand, Central/South America

5.   Northwest Asia (including Korea), North Africa

6.   China

7.   Reserved

8.   Airplanes (In-Flight Entertainment)

The use of DVD regional coding is optional for content owners, but mandatory for DVD hardware manufacturers. Content owners can publish their titles using any combination of regional codes that they choose, or none at all. DVD hardware vendors must design their equipment to support the Region Coding system.

Parental Lock Out

The DVD-Video format supports up to eight levels of parental management, also called parental lockout. Viewers can configure DVD-Video players to require a password when titles above a specific rating level (G, PG, PG-13, R, etc.) are inserted into the player. DVDVideo titles include the rating levels associated with each Title stored on the disc. The player performs a comparison of the rating levels of the content stored on the disc to the parental management level programmed into its memory by the user, and will only provide access to content that is rated equal to or lower than that value. Parental management levels vary depending on the country code of the DVD-Video player.

During the DVD-Video authoring process, only the differences between the various rating levels are encoded and stored on the disc. As an example take a title that has two different ratings, G and PG, based on the presence of a single scene that has some violence. The “G” version of the title substitutes a different, non-violent scene to preserve its G rating, while the PG version will include this scene. Both versions of the scene are encoded and stored on the DVD-Video disc. The DVD-Video author constructs two unique Program Chains, one for the “G” version and the other for the “PG” version. If the user has selected to view the “G” version, the DVD-Video control stream will play the substitute scene at the correct time. If the user has selected to view the “PG” version the original scene with some violence will be displayed.

Copy Protection

The issue of how to protect content once it is distributed on a DVD-Video disc was a major topic of discussion between members of the DVD Forum and representatives from the motion picture and software industries. The launch of the DVD-Video format in the United States was delayed almost a year in order to improve the copy protection features of DVD-Video so that it would satisfy the major motion picture studios. In late June of 1996 representatives from the computer, consumer-electronics and movie industries signed off on a technical working group report that recommended encrypting all data stored on DVD-Video discs and including decryption hardware in DVD Video players. Later that year proposals from the computer industry recommending an alternative method of encrypting portions of the video content were considered and accepted by the Technical Working Group. Finally in November of 1996 all parties agreed to a specific set of analog and digital copy protection methods.

There are currently three forms of copy protection used by the DVD-Video format, Analog Copy Protection (ACP), Copy Guard Management System (CGMS), and Content Scrambling System (CSS).

Analog Copy Protection

The analog copy protection feature of DVD-Video utilizes a proprietary copy protection process developed by Macrovision. Macrovision’s DVD copy protection system utilizes two separate copy protection technologies: Automatic Gain Control (AGC) and Colorstripe. The AGC technology for DVD is virtually identical to the Macrovision protection system that has been used to protect prerecorded VHS titles against consumer copying since 1985. The AGC system adds bipolar pulse pairs to the output video signal causing a recording VCR to record a weak, noisy and unstable signal level. The AGC system takes advantage of the difference in the way television and VCR automatic gain circuits work.

The Colorstripe^TM technology for DVD is similar to a protection method that Macrovision has implemented in digital set top boxes and digital video networks since 1994. This technology modulates the phase of the colorburst signal in a rapid, controlled manner, which causes annoying horizontal stripes on an unauthorized copy. The Colorstripe^TM technology exploits the chroma processing necessary to record and replay the color signals within the limitations of the consumer videocassette formats.

The combination of the Macrovision AGC and Colorstripe^TM copy protection technologies will degrade copies made on approximately 95% of consumer VCRs in the market. These copy protection technologies are designed to stop consumers, not professional pirates. Video engineers and others with access to sophisticated professional video equipment, such as time base correctors, can make unauthorized copies of Macrovision copy protected DVD titles.

Additional information on the Macrovision ACG and Colorstripe technologies can be obtained from:

Copy Guard Management System (CGMS)

Digital copying is controlled by information on each disc specifying if the data can be copied. This is a “serial” CGMS designed to prevent copies, or copies from copies. Of course, the equipment making the copy has to abide by the rules. Each sector of data on a DVD-Video disc includes CGMS data that defines how many times the data can be copied. The possible values are zero copies, one copy or infinite copies. If CGMS is set to zero copies then recording devices or computer operating systems should prevent that data from being copied. If CGMS is set to one copy then recording devices or computer operating systems will allow the data to be copied, but the CGMS values of the copied data will be set to zero copies so that additional copies can not be made from the first copy. Finally if CGMS is set to infinite copies then computer operating systems will allow the data to be copied, and the CGMS values will remain unchanged. CGMS information is also encoded into the analog video signal, on NTSC line 21, so that digital recorders with analog inputs can recognize it.

Content Scrambling System (CSS)

CSS uses data encryption techniques to prevent copying media files directly from the disc. All DVD-Video players have a decryption circuit that decodes the encrypted data before displaying it. DVD-ROM drives and MPEG-2 playback boards or software decoders that can be used to play DVD-Video titles exchange encryption keys so that the video is decrypted just before display by the encoder. During 1999 the Content Scrambling System was broken by a group of Linux programmers who wanted to watch DVD-Video titles on their personal computers. DeCSS, a simple hacking program to break CSS, has been published on the Internet, and several motion picture studios and the MPAA have sued these web sites in order to have these programs withdrawn. The MPAA has already been granted several preliminary injunctions directing various web sites to remove DeCSS from their servers. Unfortunately the MPAA and the courts can’t possibly keep up with the speed of the Internet, so as soon as DeCSS is removed from one web site it then appears on several new sites. In this day an age of the Wild, Wild Web it will be virtually impossible to keep copies of DeCSS, or any other program that rips or hacks DVD-Video titles off the Internet.

The DVD Forum is currently developing more secure versions of CSS, dubbed CPPM and CPRM that will be used in DVD-Audio, Universal DVD players, and DVD recording devices. Figure 2.11 shows how the current DVD-Video Content Scrambling System works.

All three methods of copy protection are optional for the producer of a disc. These copy protection schemes are designed to guard against casual copying. Professional pirates who have access to high-end video and DVD disc replication equipment will be able to defeat each of these copy protection methods easily.

Figure 2.11  DVD-Video Content Scrambling System Block Diagram

DVD-Video Video Object Format

The DVD-Video Video Object (VOB) format is an extremely powerful publishing medium. The VOB format lets you use advanced multimedia features, such as multiple video angles, multiple audio streams, multiple subpicture streams, and seamless interactive branching. While the VOB format is an essential part of the DVD-Video specification, there is a significant potential for its use outside of DVD-Video players. A number of DVD-ROM title developers will store their multimedia content in the VOB format even though their titles will not be designed to work in DVD-Video players. In the past year a number of DVD authoring tool vendors have released DVD-on-CD products that allow data stored in the VOB format to be transferred to CD-ROM, and then played back on any personal computer, even if it does not have a DVD-ROM drive or DVD-Video decoding software. As more and more companies create development and authoring tools for the VOB format, I predict that it will become a popular publishing format in its own right, independent of DVD-Video playback.

DVD Volume, Directory & File Structure

Figure 2.12 shows the volume, directory, and file structure of a DVD-Video disc. Note that the directory and filenames for a DVD-Video disc are defined in the specification. The Video_TS directory on a DVD-Video disc holds all the files that are used for the disc, and it includes three types of files. Information (.ifo) files provide all the details on how to access the content stored on the DVD disc. Backup (.bup) files are copies of an .ifo file stored in a different part of the disc for error recovery. Multimedia content to be delivered by the disc is stored in .vob files. The video_ts.ifo file contains information required to access content stored in the Video Manager area of the disc.

Figure 2.12  DVD-Video Volume, Directory and File Structure Hierarchy

The Video Manager area can include static menus or menus with video and audio content. This multimedia data is stored in the video_ts.vob file, which is accessed on a DVD-Video player through the TITLE MENU button on the remote control. A DVD-Video disc can hold up to 99 titles, each of which has its own information file. The information file for the first title on a DVD-Video disc is vts01_0.ifo, thus vts_99_0.ifo is the information file for the ninety-ninth title. Each title can include static menus or menus with video and/or audio content. This multimedia data is stored in the vts_xx_0.vob file, where xx is the title number. These title menus are usually accessed on a DVD-Video player through the MENU button on the remote control.

The main video, audio, and graphics used in a DVD-Video title are stored in the vts_xx_y.vob files, where xx is the title number and y is a number between one and nine. .vob files are limited to 1 Gb or less in size, so a title with a lot of video and audio content will require a number of .vob files. For example, a full-length movie published on a DVD-5 disc will typically have five .vob files within the main title — vts_01_1.vob, vts_01_2.vob, vts_01_3.vob, vts_01_4.vob, and vts_01_5.vob. The first four .vob files would each be 1Gb, while the last file would be less than 1Gb. If the title developer includes additional content or trailers these are normally stored in a separate video title set and thus would have require a different set of .vob files.

DVD Video Manager

The Video Manager, shown in Figure 2.13, acts like a table of contents for all the data stored in the DVD-Video area of the disc. It includes up to eight different data tables stored in the video_ts.ifo file. Three of these tables are mandatory, two are optional, and three are required only if the Video Manager area includes a static or dynamic menu. The order of the data in the tables is typically as shown in Figure 2.13. Each table in the Video Manager file performs the following function.

1.   The Video Manager Information Management Table (VMGI_MAT) provides information on the size of the video manager file, the start address of each table in the Video Manager file, and information about the DVD-Video title such as the number of titles, a volume set identifier, etc.

2.   The Title Search Pointer Table (TT_SRPT) provides information on each title included on the DVD disc, such as the type of title (sequential or random), the number of video angles, the number of chapters, the parental ID code, and the start address of the video title set.

3.   The Video Manager Menu Program Chain Information Unit Table (VMGM_PGCI_UT) provides information on the different menu languages used in the title menu (if it exists).

4.   The Parental Management Information Table (PTL_MAIT) provides information on the parental levels defined for the Video Manager and each title (if parental levels are used).

5.   The Video Title Set Attribute Table (VTS_ATRT) provides information on the attributes and start address of each video title set.

6.   The Text Data Manager (TXTDT_MG) provides information such as volume name, title name, producer’s name, and textual descriptions for each title.

7.   The Video Manager Menu Cell Address Table (VMGM_C_ADT) provides the start and ending address of all cells used in the video manager .vob files, if they exist.

8.   The Video Manager Menu Video Object Unit Address map (VMGM_VOBU_ADMAP) provides the start address of all video object units used in the video manager VOB files, if they exist.

Video Title Set Information

The Video Title Set Information (vts_xx_y.ifo) file contains information required to access and play each of the video titles stored on the disc. This file includes up to nine tables, as shown in Figure 2.14. The order of the data in the tables is typically as shown in Figure 2.14. Each table in the Video Title Set Information file performs the following function.

1.   The Video Title Set Information Management Table (VTSI_MAT) provides the start address of each of the tables in the vts_xx_y.ifo file, as well as information about the title such as the number of audio and subpicture streams.

2.   The Video Title Set Part of Tide Search Pointer Table (VTS_PTT_SRPT) provides the start address of each chapter within the title.

3.   The Video Title Set Program Chain Information Table (VTS_PGCIT) provides information for each of the program chains in the title.

4.   The Video Title Set Menu Program Chain Information Unit Table (VTSM_PGCI_UT) provides information on the existence of Root, Subpicture, Audio, Video Angle, and Chapter menus, and the start addresses, if they exist, for each title.

5.   The Video Title Set Time Map Table (VTS_TMAFT) provides the start address for each title’s timetable, the units of measurement for the time map entries, and up to 2,048 time-map entries to allow searching through the title based on time.

6.   The Video Title Set Menu Cell Address Table (VTSM_C_ADT) provides the start and end address of each cell in the vts_xx_0.vob file (if it exists).

7.   The Video Title Set Menu Video Object Unit Address Map (VTSM_VOBU_ADMAP) provides the start address of each video object unit in the vts_xx_0.vob file (if it exists).

8.   The Video Title Set Cell Address Table (VTS_VOBU_ADT) provides the start and end address of each cell in the vts_xx_y.vob file.

9.   The video title set video object unit address map (VTS_VOBU_ADMAP) provides the start address for each video object unit in the vts_xx_y.vob file.

Figure 2.13  DVD Video Manager (VMG) Structure (See color insert for color version of this figure.)

Video Object Set

Video Objects are the basic multimedia data type for the DVD format. A VOB includes one video stream, up to eight audio streams, up to 32 subpicture streams, and the navigation information required to connect video objects into program chains, titles, and title sets. Figure 2.15 shows the basic construction of a Video Object Set (VOBS). There are some restrictions on the data rate requirements of a Video Object Set and each of its component multimedia data types.

•   The total data rate of a Video Object Set can’t exceed 10.08Mbps.

•   The maximum data rate of the video stream within a Video Object Set is 9.8Mbps.

•   The maximum data rate for a single audio stream in a Video Object Set is 6.144Mbps.

•   The maximum total data rate for all eight audio streams is 9.8Mbps.

•   The maximum data rate for a single subpicture stream within a Video Object Set is 3.36Mbps

•   The maximum total data rate for all subpicture streams is 9.8Mbps.

Figure 2.14  DVD Video Title Set Information (VTSI) File Structure (See color insert for color version of this figure.)

As discussed previously and shown in Figure 2.6, a Video Object Set is a collection of VOBs. Video Objects may be divided into cells, each of which is made up of a collection of Video Object units. A Video Object Unit (VOBU) is a sequence of packs, roughly equivalent to a sector on the DVD disc, and will include approximately 0.4 to 1.2 seconds of content. Video Object Units consist of a stream of navigation packs (NV PCK), video packs (V PCK), audio packs (A PCK), and subpicture packs (SP PCK). Video Object Units start with one navigation pack followed by a series of video, audio, and subpicture packs, if required. The Video Object Unit ends immediately before the next navigation pack, or at the end of the Video Object Set.

Figure 2.15  DVD Video Object Set Structure – The basic building block of DVD-Video

Why Is It So Complicated?

By now you re probably thinking that using the DVD Video Object format would be a big mistake. Why is it so complicated? Why are there so many different levels of structure, and why are there so many different terms? The DVD Video Object format is designed to deliver an unprecedented combination of video, audio, and graphics data types, at broadcast quality, with near-real-time switching between data streams. As you can see from Figure 2.15, the Video Object Unit, which is the basic building block of DVD-Video, is actually a multiplexed combination of video, audio, subpicture, and navigation data streams. The individual data packs are small enough so that a DVD-Video player, or a DVD-ROM computer system, can switch playback streams in real time, providing seamless playback from a multitude of video, audio, and subpicture streams.

The advantages of using the VOB format are tremendous: nine broadcast-quality video streams, eight theatre-quality audio streams, 32 high-resolution graphics overlay streams, and seamless branching between any of these streams. Perhaps the biggest advantage is that every DVD-ROM computer system available today has built-in software that handles the VOB format. The disadvantages of using the VOB format are not insignificant. You’re required to use directory and file naming conventions of the DVD-Video specification, a complicated hierarchy that is not easy to understand, and it costs more to create your multimedia data files in the VOB format. These disadvantages will be minimized as new, low-cost tools come to market. Authoring tools will hide the complexities of the DVD-Video specification, and the tools you use to generate DVD-Video-compliant files can be expected to drop in price.

DVD-ROM

DVD-ROM is a high capacity, high throughput read-only optical-disc format that can be used as a general-purpose computer storage device. The DVD-ROM format book does not discuss the application programs or content that may be published in the DVD-ROM format. This means that the DVD-ROM format can be used for a wide variety of purposes within a personal computer environment.

The vast majority of DVD-ROM enabled personal computers sold today include hardware or software for playback of DVD-Video titles. In general a personal computer with a 400 MHz or faster CPU can play DVD-Video titles with a “software-only” DVD decoder, while slower systems will need an add-in card to help the CPU decode the MPEG-2 video and Dolby Digital audio streams in real time. Figure 2.16 illustrates the configuration of a DVDROM enabled PC with an add-in card for hardware DVD decoding. Personal computers that use software decoding will have the same basic configuration, except the add-in card will not be required to deliver acceptable playback performance.

Figure 2.16  DVD-ROM Enabled Personal Computer Diagram

DVD-Audio

DVD-Audio is designed to replace CD-Audio as the primary prerecorded music format. Like DVD-Video, DVD-Audio is built on the foundation of DVD-ROM. So a DVD-Audio disc is actually a DVD-ROM that includes a zone of material supported by the DVD-Audio specification, and may or may not also contain a zone of DVD-Video material. These zones are held in the Audio_TS and Video_TS directories on the DVD disc.

DVD-Audio incorporates many DVD-Video navigational and architectural features, but it also includes several new interactive and playback features, such as still graphics slide shows. It also supports higher audio fidelity and more flexible multi-channel playback options than DVD-Video. Thus, while the two formats are closely related, DVD-Audio extends DVDVideo to create a truly distinct product tailored for audio-centric applications.

DVD-Audio Features

In developing the DVD-Audio format, the DVD Forum began with a specific set of desired features. The most important of these were:

•   High Quality Audio — DVD-Audio is designed to support the very highest quality audio possible.

•   Multi-Channel Audio — DVD-Audio is designed to permit extensive multi-channel capabilities, and recognizes that multi-channel programs might be played back in venues where only stereo monitoring is available.

•   Additional data — DVD-Audio is designed to support synchronized text data, still images and video.

•   Navigation — DVD-Audio is designed to support navigation similar to the DVD-Video format.

•   Simple Interface — DVD-Audio is designed to support a simple CD player-like interface for playback settings.

•   DVD-Video Compatibility — DVD-Audio is designed to be broadly compatible with DVD-Video and permits utilization of DVD-Video features, where appropriate.

•   Copyright — DVD-Audio is designed to support effective anti-copying and anti-piracy measures.

DVD-Audio Players

To ensure DVD-Audio’s flexibility across a wide range of applications, the DVD Forum decided not to define a mandatory set of features for all DVD-Audio players. Instead, a DVDAudio disc can include a variety of different content types, each of which will play back on one or more of several different players. The primary distinction between different players is the availability of a video display device. For a new audio format, it is essential to support playback without a video display, such as in a car, or with a portable player.

The DVD Forum defined five player types that might possibly be used to play back content from a disc in DVD-Audio format. These include:

•   A “simple” Audio-only player that has no video output, and navigates the disc linearly using a list of tracks similar to the Table of Contents on a CD.

•   A “smart” Audio-only player that gives the user more choices of how to navigate the material on the disc, and may include an LCD display to show song titles and other textual information such as lyrics, but does not include a video display.

•   An “Audio-with-Video” player that supports navigational choice and includes video outputs to support multimedia, including visual menus, album artwork, “slide show” graphics and motion video.

•   A “Universal” player that offers the same audio and multimedia support as the Audio-with-Video DVD-Audio player, but also plays DVD-Video discs.

•   A DVD-Video player, which could be used to play optional video content that has been included on a DVD-Audio disc. Note that DVD-Video players will not be able to play the content stored in the DVD-Audio zone on the disc.

Figure 2.17 illustrates the type of DVD discs that most common DVD player types (DVD-Audio, Universal DVD, DVD-Video, and DVD-ROM) can accept. At the time this book was published most DVD-ROM enabled personal computers can’t play DVD-Audio discs since neither Microsoft nor Apple has released DVD-Audio drivers for their consumer operating systems.

Most industry experts agree that the most common type of DVD-Audio players will be the “Audio-Only” and “Universal” player described above. A summary of the major features of DVD-Audio is shown in Table 2.4.

Figure 2.17  DVD-Audio Player and DVD Disc Type Matrix

Table 2.4 DVD-Audio Feature Chart
DVD-Audio Parameter	Audio Objects	Video Objects
Coding Mode	LPCM or MLP	LPCM or Dolby Digital
Sampling frequency (kHz)	44.1/48/88.2/96/176.4/192	48/96
Bits per Sample	16/20/24	16/20/24
Maximum # of Channels	6 (up to 96 kHz) or 2 (176.4/192 kHz)	8
Maximum Bit Rate	9.6 Mbps	6.144 Mbps

DVD-Audio Formats

DVD-Audio’s primary media content is audio so the specification attempts to deliver the highest possible audio fidelity, and thus focuses primarily on uncompressed PCM audio. PCM audio may be stored in either of two forms: linear (LPCM) or “packed” using MLP. DVD-Audio Players are required to support both LPCM and MLP audio in either stereo, or multi-channel configurations. DVD-Audio Players may also, at the manufacturer’s discretion, support optional audio formats such as Dolby Digital, or DTS. A DVD-Audio disc may offer up to two audio streams in any given program. The first stream is required to be PCM (stereo or multi-channel), while the second stream may be one of the optional audio types. It is likely that Universal players will support LPCM, MLP, Dolby Digital and DTS, as these will be commonly used for both DVD-Audio and DVD-Video titles.

DVD-Audio’s PCM support covers two “families” of sample-rates. One family is based on the 44.1 kHz rate of CD-Audio, and also includes frequency multiples of 88.2 kHz and 176.4 kHz. The other family starts with the 48 kHz rate required in the DVD-Video format, and adds 96 kHz and 192 kHz. DVD-Audio also includes support for several word-lengths, including not only the 16-bit samples used in CD-Audio, but also 20-bit and 24-bit samples as well.

Of all of DVD-Audio’s features, the one that consumers are generally expected to find most appealing is the format’s ability to deliver multi-channel sound. In each sample-rate family, the highest sample-rate (176.4 kHz or 192.0 kHz) is supported only for mono or stereo playback. The rest of the rates (44.1 kHz, 48 kHz, 88.2 kHz, and 96 kHz) are supported for mono up through six channels.

DVD-Audio’s maximum data-rate that can be used for audio is 9.6 Megabits per second. This places limits on the total data bandwidth available to spread among the channels. Six channels of 20-bit audio at either 88.2 kHz or 96 kHz, for instance, would substantially exceed the format’s data-rate. The specification offers two strategies for dealing with this bandwidth limitation. One is MLP, and the other is called mixed resolutions.

Mixed resolutions allow the producer to prioritize the allocation of bits among channels in a given audio track. Each channel is assigned to one of two “Channel Groups,” with the resolution of Group 1 always equal to or better than that of Group 2. Within a given track, the sample-rates used for all channels in both groups must be from the same family. Assignment of channels to groups, and selection of attributes within each group, may be changed on a track-by-track basis. To regularize the use of mixed resolutions among channels, most—but not all—of the reasonably foreseeable possibilities for varying the resolution of up to six channels are defined in the DVD-Audio format’s 21 supported channel configurations.

As shown in Table 2.5, DVD-Audio is capable of delivering longer playing times than CD-Audio’s 74 minutes. But even with DVD-Audio’s greater data rate and data capacity, full support for high-fidelity surround sound (six channels of 24-bit/96 kHz audio, for instance) would exceed the format’s maximum bit-rate and quickly use up the available storage. To address this issue, the DVD Forum adopted the MLP compression system. Because it is a completely Lossless system, a decoded MLP datastream is bit-for-bit identical to the pre-encoded PCM source stream. Table 2.5 assumes an average compression ratio from the MLP codec.

MLP permits substantial reduction in the bandwidth required to store high-quality multichannel PCM audio. The efficiency of the algorithm varies with the program content, but in many cases MLP has reliably achieved a 45% reduction in bandwidth requirements. This allows a DVD-5 disc to be used for presentation of up to 74 minutes of audio content using six channels of 24-bit, 96 kHz audio. DVD-Audio discs are not required to use MLP, but decoding capability for MLP is mandated for all DVD-Audio players.

To ensure that a DVD-Audio disc will always play, regardless of the available monitoring configuration, the DVD Forum defined how a player should present multi-channel programs in situations where only stereo playback is available. Many programs mixed for surround presentation will not sound correctly balanced in stereo. Thus DVD-Audio allows both stereo and multi-channel mixes of the same music to be delivered on one disc. Additionally the DVD-Audio specification requires that all players support an approach called “SMART Content” (System Managed Audio Resource Technique).

Table 2.5 Sample Playback Times for Various DVD-Audio Configurations

SMART uses a set of “coefficients” defining the relative level, panning and phase that will be applied to each channel of a multi-channel mix if it is combined into stereo. A SMART “downmix” will only be played if a discrete 2-channel mix of a given program has not been included on the disc. This provides a simple method to control the sound of the music in cases where the multi-channel mix is downmixed by the player.

While audio playback is at the heart of DVD-Audio, the format is also intended to offer a playback platform for the kinds of value-added multimedia features that have proven difficult to deliver to the mass market on formats such as CD-ROM and Enhanced CD. These features include graphical accompaniment for the music, textual information about the music and the artist, and motion video such as music videos or interviews. The DVD-Audio specification supports the display of still pictures during audio playback, and offers a wide range of options as to when and how the pictures are shown. Still images in DVD-Audio are encoded in MPEG-2. The basic graphical unit is an ASV (Audio Still Video), composed of an MPEG encoded still image; a subpicture overlay (SPU), and Highlight Information (HLI). The subpicture and highlight layers are optional.

ASVs are grouped into sets of graphics referred to as ASVUs (Audio Still Video Units), each of which may contain up to 99 ASVs (individual images). While the data size of an individual ASV may vary greatly, typical ASVs may be expected to average about 100 Kbytes. The total size of an ASVU may not exceed 2 Mbytes, which is the size of the buffer that player manufacturers are required to provide to allow ASVUs to be preloaded into player memory, so you should plan on having about 20 ASVs per ASVU. This preloading process ensures that players will not interrupt audio playback in order to read graphical data from the disc. This will allow the listener to browse a series of still graphics without affecting the currently playing song. For each ASVU, the producer defines a playback mode that determines the order and duration of graphical display. “Browseable” graphics have a defined minimum and maximum on-screen duration, but allow the user to skip forward through the set of images by using the remote control. “Slideshow” graphics, on the other hand, are displayed for a predetermined amount of time.

Within each of these modes the order in which the images is displayed is defined as “sequential”, “random,” or “shuffle”. The DVD-Audio format supports a variety of start and end effects (wipes and dissolves) as transitions between images. The specification also allows the highlights within a given ASV to change over time. This is useful for content such as song lists, lyrics or libretto. Links allowing listeners to navigate to different parts of a song by clicking on lyrics are expected to be a common feature of DVD-Audio titles.

The DVD-Audio specification provides for storage of textual information on disc, though inclusion of text is not mandatory. Text support is provided for multiple “language units,” with up to eight languages available on any given disc, and two character types are supported. For languages such as English that use single-byte characters (ISO8859-1), text is structured for presentation as “pages” of four lines of up to 30 characters each. Japanese and other languages using double-byte characters are organized into pages of two lines of up to 15 characters each.

The DVD-Audio specification defines two distinct types of text. Audio Text Data is intended for display of static information that is not synchronized to the audio program. If Audio Text Data is used at all, it must include the Album title, “Group” name and Track name. It may also include optional information such as the name(s) of the artist and composer. Up to 64 Kb of data may be included for each language unit.

Real Time Text is stored on disc as part of the audio stream, and may be synchronized to audio playback. Ideal for lyrics and libretto, Real Time Text may also be used for context-dependent commentary such as running liner notes. The extent to which a given player supports Real Time Text or Audio Text Data is up to the hardware manufacturer.

Video on DVD-Audio

DVD-Audio’s support for video is similar to that of DVD-Video, using VOBs comprised of MPEG-2 video plus audio and optional subtitles. However, some advanced features that are supported in DVD-Video, such as parental control and complex interactivity, are not supported in all DVD-Audio settings.

DVD-Audio includes a feature called the SAMG (Simple Audio Manager). Containing a list of up to 314 tracks, it serves the same function as the table of contents on a CD-Audio disc. Simple Audio-only players look at the SAMG to find the information they need for linear, track-based navigation of the disc. “Smart” Audio-only players, Audio-with-Video players and Universal players all support more sophisticated navigation than do simple Audio-only players. The directory information these players need is found in the AMG (Audio Manager). Smart Audio-only players use a section of AMG designated as AOTT, while Audio-with-Video players and Universal players use the AVTT section. Simple Audio-only players, meanwhile, ignore AMG completely.

DVD-Audio titles include two domains: AMG and Audio Title (ATT). The presentation data referenced from AMG is contained in a VOBS. The presentation data referenced from ATT is contained in one or more Audio Object Sets (AOBS). Each AOBS is comprised of some number of Audio Objects (AOBs). AOBs are made up of one or more tracks of audio, optionally accompanied by still images and/or Real Time Text.

DVD-Audio players that read AMG are able to take advantage of DVD-Audio’s capacity to organize material hierarchically. This logical hierarchy exists in parallel to the format’s data structure. It is based on five different levels: album, group, title, track and index. Each side of a DVD-Audio disc contains one album. Each album may contain up to nine groups, essentially a play list specifying the playback order of a number of titles. While any title may contain up to 99 tracks, there may be no more than 99 tracks total within a single group.

As on a CD, a track may be thought of as a single audio program. Audio attributes such as channel configuration, sample-rate, and word-length may be changed on track boundaries. An index is a reference point to a portion of an audio track, and there may be up to 99 indices within a single track. Because a group is simply a play list, more than one group may reference an individual track. On an album with twenty audio tracks, for instance, one group might be a sequence of all the songs, another could be a play list of just acoustic numbers, and a third might be a play list of just dance tracks. Groups thus allow up to nine different listening experiences drawn from one underlying set of material.

DVD-Audio discs are required to include three different content directories to facilitate navigation on different types of players. Simple Audio-only players use SAMG. SMART Audio-only players use AMG/AOTT. Players with a video output use AMG/AVTT. In players that use AVTT, navigation is supported via a visual menu like those used in DVD-Video. AOTT machines can’t use visual menus, but the underlying method of enabling navigation is the same. As with DVD-Video players, navigation of the content referenced in both AVTT and AOTT is based on program-chains that are instructions to tell the player what to play and when to play it.

The DVD-Audio specification includes a set of Navigation Commands, as well as General and System parameters that are stored in player memory. As with DVD-Video, the commands are broken into various categories (Link, Jump, GoTo, SetSystem, Set and Compare), but the navigation commands supported in DVD-Audio are a subset of the DVD-Video set. The availability of nine groups allows navigation that is far more varied than that of CD-Audio, but the possibilities are more limited than in DVD-Video.

Among the most important navigational constraints in DVD-Audio are those relating to movement within a Group. A user may enter a Group at any point by selecting a specific track. But once playback has started within a given Group, that group will continue playing in order through to the end, unless the user exits playback by using the Menu or Group button on the remote to go to the album’s main menu. The specification makes no provision for linking directly from a given Group to content outside that Group.

One important aspect of DVD-Audio Groups is that they may include audio tracks drawn from AOBS, as well as Video Title Sets (VTS) from a disc’s optional Video zone. A VTS on a DVD-Audio disc is similar to a VTS on a DVD-Video disc, but there are a number of important distinctions in the video capabilities of the two formats. First, video title sets on a DVDAudio disc do not include an individual menu (VTSM); the only menu in the Video zone on a DVD-Audio disc is the VMGM.

Second, the DVD-Audio specification requires that every audio program include a PCM stream, even content in the DVD-Video zone of the disc if they are to be played on Audio Only DVD-Audio Player (AOTT). If the DVD-Video soundtrack is not intended for playback on Audio-only players, a PCM stream is not required.

Like DVD-Video menus, DVD-Audio menus may use motion video backgrounds. The only domain on a DVD-Audio disc from which motion video is never referenced is ATT. Therefore video may be used in the AMG menu (AMGM), the VMG menu, or a Video Title. The domain in which the DVD-Audio specification is most restrictive with video is VTS. Also, DVD-Audio does not support pre-commands or post-commands, as well as the use of dummy PGCs that are used to transition between domains in DVD-Video titles. Thus video title sets on DVD-Audio discs are less capable of complex interactivity than those on DVDVideo discs.

DVD-R

DVD-R is a high capacity, high throughput write-once/read-many (WORM) optical-disc format that can be used as a general-purpose computer storage device. The DVD-R standards have been approved and are now at Revision 2.0, which introduced DVD-R for Authoring and DVD-R for General media types. Initially DVD-R devices had a storage capacity of approximately 3.68 GBytes per side. Total capacity was increased to 4.37 GBytes per side within a year of the initial shipment of DVD-R devices.

Recording on DVD-R discs is accomplished through the use of a dye-polymer recording layer that is permanently transformed by a highly focused red laser beam. This dye polymer substance is spin-coated onto a clear polycarbonate substrate that forms one side of the “body” of a complete DVD-R disc. The substrate is injection molded, and has a “pre-groove” spiral track formed onto its surface. This “pre-groove” is used by a DVD-R drive to guide the recording laser beam during the writing process, and also contains recorded information after writing is completed. A thin layer of metal is then sputtered onto the recording layer so that a reading laser can be reflected off the disc during playback. A protective layer is then applied to the metal surface, which prepares the side for bonding into a complete DVD-R disc.

These steps are done for each side of a disc that is required for recording. If only a single recording side is required, the opposite side can contain a label or some other visible information such as pit art. If both sides are needed for recording, then two recordable sides can be bonded together. In this case each side must be read directly (by flipping over the disc) as dual layer technology is currently not supported for DVD-R discs.

The recording action takes place by momentarily exposing the recording layer to a high power (approximately 10 milliwatt) laser beam that is tightly focused onto its surface. As the dye polymer is heated, it is permanently altered such that microscopic marks are formed in the pre-groove. These recorded marks differ in length depending on how long the write laser is turned on and off, which is how information is stored on the disc. The light sensitivity of the recording layer has been tuned to an appropriate wavelength of light so that exposure to ambient light or playback lasers will not damage the recorded information.

Using the first generation Pioneer drive (DVR-S101) a full capacity 3.68 GByte disc can be written in approximately 50 minutes in a disc-at-once recording, regardless of the data that will be contained. Using the second generation Pioneer drive (DVR-S201) a full capacity 4.37 GByte disc can be written in approximately one hour. Using the third generation Pioneer drive (DVR-A03) a full capacity 4.37 GByte disc can be written in approximately 30 minutes. Recorded DVD-R discs support “UDF Bridge” file system.

DVD-R discs can be played on almost all DVD-Video players, as well as the vast majority of personal computers equipped with a DVD-ROM drive. There are a number of older DVDVideo players that will not recognize a DVD-R disc when it is inserted into the player. Newer DVD-Video players have better DVD-R compatibility, but there are still some players on the market today that can’t reliably read DVD-R discs. There is no fundamental requirement for a DVD-Video player to support the playback of any discs other than those in the DVD-Video format. Recently the DVD Forum has undertaken a new initiative called DVD Multi-Read, which is designed to encourage player manufacturers to design their hardware so that it will read all CD and DVD optical disc formats. Player that comply with the DVD Multi-Read initiative will be able to display a logo which will help consumers to identify which players can read all DVD formats.

There are three fundamental applications for DVD-R: Testing and development, Distribution, and Storage and archival.

Testing and Development Many DVD applications utilize replicated read-only discs that are mass-produced and distributed to a large number of users. Preparation of the content to be published can be a complex and time consuming process that must be completed accurately to avoid errors or functional defects. Mastering and set-up efforts required for replication of a DVD disc range from $1,000 for DVD-5 discs to $4,000 for DVD-9 discs. Thus DVD-R provides a more cost effective method of testing content prior to mass production. A single low cost disc can be quickly written and tested in a DVD-Video player or DVD-ROM enabled personal computer. While it is not possible to create a dual layer DVD-R at this time, many developers simply split their DVD titles into two sections in order to test the entire title on two DVD-R discs.

Distribution DVD-R’s low-cost media and relatively portable recording equipment can aid small-scale distribution of DVD content. DVD mastering and replication expenses can be prohibitive when only a single disc or very small quantity is required. DVD-R allows discs to be recorded at the desktop level, which can result in very quick turnaround and significantly lower cost. Some users may not be comfortable with sending sensitive data files or other work in progress to an outside facility for replication, so the ability to maintain continuous inhouse control of this information can be crucial. This is particularly true with classified data maintained by Government agencies. Complete confidentiality is afforded by DVD-R because it can be maintained as a completely in-house process.

Storage and Archival DVD-R media provides archival lifetimes equal to or better than CD-R, which has been calculated to be 100 years. Thus, DVD-R is suitable for long-term archival of information that can be stored digitally. This includes image data, film and video archives, or any other media that need to be retrieved more easily by users. DVD-R’s high capacity makes it especially suitable for storing large files that do not fit onto a single CD-R volume, thus creating new opportunities for inexpensive storage of these assets. Since DVD discs are dimensionally identical to the CD family of discs, they have the advantage of being compatible with existing CD-based jukebox and changer mechanisms. This allows automated retrieval of recorded DVD-R volumes in networked environments, with a seven-fold increase in storage density as compared with CD-R technology.

In 1998 Pioneer released the DVR-S101 external SCSI-2 DVD-R device that is capable of storing up to 3.68 GBytes of data on a single layer, single sided DVD-R disc. The unit was available for a retail price of $17,000. Blank DVD-R discs were originally priced at $50 per disc. In 1999 Pioneer released the DVR-S201 external SCSI-2 DVD-R device that is capable of storing up to 4.37 GBytes of data on a single layer, single sided DVD-R disc. The unit was available for a retail price of $5,400. Blank DVD-R discs were then priced at $35 per disc. In early 2001 Pioneer released the DVR-A03 (an OEM product) and the DVR-103 (an after market product) internal IDE DVD-R and DVD-RW device that is capable of storing up to 4.37 GBytes of data on a single layer, single side DVD-R or DVD-RW disc. The unit is currently available for a retail price of less than $1,000 and blank discs are priced below $10 per disc.

DVD-R Media Types

In early 2001 a second type of DVD-R media was released, called DVD-R for General. The original DVD-R media was renamed DVD-R for Authoring. The two types of DVD-R media have the same storage capacities, and in general work in the same DVD-Video players and DVD-ROM PC drives.

The most significant technical difference between the two types of media is the wavelength of the laser used to record data on the disc. The main reason that the DVD-R for General format was introduced is for copy protection. DVD-R for General media is designed in a way that prevents a bit for bit copy of data from a CSS encrypted DVD-Video title onto a blank DVD-R for General disc. Additionally the DVD-R for Authoring media has been enhanced through the addition of a new Cutting Master Format that will allow DVD-R for Authoring media to be used by DVD replication facilities for mastering. Thus DVD-R for Authoring media will become an acceptable alternative to DLT tape for delivering the master disc image to a DVD replication facility. A portion of the lead-in area of a DVD-R for Authoring disc is used to store the Disc Description Protocol (DDP) data required by disc replication facilities.

DVD-R for General discs are recorded using a 650 nm laser, while DVD-R for Authoring discs are recorded using a 635 nm laser. Essentially this means that only certain types of DVD-R drives can be used to record each DVD-R media type. The Pioneer DVR-S101 and DVR-S201 DVD-R drives must be used to record DVD-R for Authoring Media. The Pioneer DVR-A03, DVR-103 drives and the DVR-2000 set top recorder must be used to record DVD-R for General Media.

DVD-RAM

DVD-RAM is a high-capacity, high-performance optical disc that allows data to be read, written and erased. It is designed to work exactly like other writeable removable media such as floppy or Zip disks. DVD-RAM allows users to copy and delete files, and run programs. DVD-RAM offers all of the benefits of DVD, including high capacity, compatibility with CD formats, and enhanced rewriteability. Panasonic and Toshiba released the first DVD-RAM drive in 1998, and a number of additional companies have released both DVD-RAM computer and home entertainment products in the last several years. A sample DVD-RAM drive and media are shown in Figure 2.18.

With capacities of 2.40 GBytes to 8.75 GBytes per disk, DVD-RAM offers up to eight times the storage of a rewriteable CD. DVD-RAM is cheaper than a conventional magneto-optical disc drive; at less than one penny per megabyte it is the one of the most economical rewriteable mediums available today. DVD-RAM drives can read all of the CD and DVD formats including CD-ROM, CD-Audio, CD-R, CD-RW, DVD-ROM, DVD-R, and DVD-RW, making it an ideal choice for high-density data storage and exchange.

DVD-RAM drives use phase-change technology in which a laser heats the inner surface of the disc to magnetically charge it. This allows the data to be rewritten hundreds of thousands of times. A “wobble-land-groove” format, shown in Figure 2.19, provides clocking data, with marks written on both the grooves and the lands between grooves. The grooves and pre-embossed sector headers are molded into the disc during manufacturing. The DVD-RAM wobble-land-groove format or track structure makes DVD-RAM technology reliable, and the constant linear velocity format provides high access speed and capacity.

Figure 2.18  DVD-RAM Drive and Media

DVD-RAM discs consist of double layers of metallic film embedded in hard plastic. The drive motor constantly changes the disc’s rotational speed to compensate for the location of data on the disc. A laser uses light of varying intensities to write and erase data. The metallic layers in the disc are made of a crystalline material that reflects light. To write data, the laser heats a metallic layer to 900 to 1,300 degrees Fahrenheit and creates pits in the surface. To erase or change data, a weaker laser beam heats the pits to approximately 400 degrees Fahrenheit.

Single-sided DVD-RAM discs, shown in Figure 2.18, come with or without cartridges and can be read by some “newer generation” DVD-ROM drives. There are two types of cartridges: type 1 is sealed and type 2 allows the disc to be removed. The transfer rate for DVD-RAM is determined by the media specification. The 2.40 GBytes disc has a 1,385KB/sec. transfer rate, and the 4.37 GByte disc will have a 2,770KB/sec. transfer rate. Access times will also evolve with an increase in disc rotational speed, reducing drive latency. Further reductions in access time will come from mechanical improvements, a more robust servo technology and mass reductions in the optical pickup.

DVD-RAM is designed to meet the requirements of mass commercial and consumer audiences, differing from the other writeable DVD standards in several ways. First, it provides random access rewriteability, like a floppy disc drive, making it suited for use and re-use by consumers. The low cost of both the drive and media make it a good choice for a wide audience of users, even those that are value-conscious. DVD-RAM drive shipments began in 1998, and more than 100,000 units were shipped that year.

DVD-RAM is designed to playback all DVD-ROM applications and is intended for use in desktop storage, data exchange, backup and archiving applications. Because of the wide variety of suitable applications, a DVD-RAM drive could be used as a viable replacement to do the job of several other devices, such as CD-ROM, CD-R, optical disc, tape, removable hard drive and floppy drive storage. DVD-RAM is an excellent choice for backup and archiving. At less than a penny per megabyte, cartridges are extremely inexpensive. Given the well-established durability of optical media, they are also far more reliable than tape, the only cost-competitive alternative. Since cartridges can be stored anywhere in a home or business environment, adding to archives or retrieving files from backup is infinitely easier than doing so from tape.

Figure 2.19  DVD-RAM Wobble Land Groove Format

With their high capacity and rewriteability, DVD-RAM discs have excellent potential for many markets, such as education and entertainment. They also can be used for personal multimedia publishing, in applications such as presentations, sales tools, training and corporate communications. Future set-top box applications will give users the capacity and bandwidth to download or record their favorite movies. Research firm Disk/Trend expects traditional magneto-optical drives to be displaced by DVD-RAM drives after 1999, and DVD-RAM to begin its run as the dominant product in 1999. Disk/Trend predicts that DVD-RAM will remain the dominant DVD rewriteable format due to its current market predominance, with major growth beginning in 2000. It is difficult to say what the future holds for DVD-RAM. There are so many options for consumers who need recordable storage, including CD-R, CD-RW, Zip, Jazz, DVD-R, DVD-RAM, DVD-RW and DVD+RW to name a few. For the next few years DVD-RAM will compete directly with CD-R and CD-RW, which are extremely popular with consumers due to their low cost and almost universal playback compatibility.

DVD-RW

DVD-RW is a Rewriteable medium that allows users to record, erase and re-record their own DVD discs. The DVD-RW format was added to the original five DVD formats (DVD-ROM, DVD-Video, DVD-Audio, DVD-R and DVD-RAM) several years after their initial release. Despite DVD-RW’s late arrival it has been designed to merge with the previous DVD formats. As with DVD-R, DVD-RW’s primary goal is to provide a user-recordable medium that is physically compatible with existing DVD-Video players and DVD-ROM enabled personal computer systems. DVD-RW discs can hold up to 4.37 GBytes bytes of data per side, and can be used to store video, audio or any other type of data. Pioneer is the current leader in developing DVD-RW products although several other companies have announced their intent to release DVD-RW products during the second half of 2001.

DVD-RW uses a phase change technology for reading, writing and erasing information. Phase change technology takes advantage of materials that exhibit different reflectivity characteristics in the crystalline and non-crystalline (amorphous) states. A 650-nanometer wavelength laser beam heats a phase change material to change it between a crystalline (reflective) and amorphous (non-reflective) state. The resulting difference between the reflectivity of the two states of the phase change material is how a player or drive can read the stored information. There are two distinct power levels used for writing and erasing data on a DVD-RW disc. The highest power level causes the surface of the phase change material to become less reflective, while a lower, or intermediate, power level will cause the material to become more reflective. Since the intermediate power level must be reached before the writing power, direct overwriting of the phase change media can be achieved. This is a critical advantage of phase change technology.

Phase change technology can achieve a relatively high disc reflectivity ratio, making it suitable for use with traditional DVD players or DVD-ROM drives. The DVD-RW specification requires a reflectivity ratio of 18% to 30%, which is identical to the DVD-ROM, DVD-Video and DVD-Audio disc specifications. Thus DVD-RW discs can in theory be played back on all DVD players and DVD-ROM enabled personal computers. However in the real world there are some exceptions to achieving full compatibility between existing DVD playback equipment and DVD-RW discs. Some DVD players incorrectly detect that a DVD-RW disc is actually a manufactured dual layer (DVD-9) disc, causing the player to try to locate a second data layer which does not exist on DVD-RW discs. Another potential compatibility problem is that some players detect the disc type by reading an identification code that is present on all DVD media types. Since DVD-RW is a new format, some older players or ROM drives will not recognize the new DVD-RW identification code, and thus reject the disc. In most cases these problems can be corrected by having the DVD-ROM drive or DVD-Video player firmware updated to a version that supports DVD-RW.

DVD-RW media can provide more than 1,000 rewrite cycles without any signal degradation. The result is a useable life better than magnetic tape, but not as good as a traditional computer hard drive. Beyond 1,000 rewrite cycles the phase change media begins to lose its efficiency and the recorded data can begin to exceed the tolerances specified by the various DVD format specifications.

The DVD-RW specification includes support for Content Protection for Recorded Media (CPRM). CPRM is designed to prevent illegal copying of content that has been encrypted using the DVD-Video CSS. CPRM also provides a mechanism for copying and subsequently protecting “copy-once” content. The major features of CPRM include:

•   Media type identification that allows a player or ROM drive to recognize that the disc is DVD-RW media. If copy protected data has been recorded onto DVD-RW media then the player or ROM drive should refuse to play back the disc.

•   A pre-embossed area on the DVD-RW disc will prevent copying of the decryption key information stored in the disc’s control data zone in the lead-in area. This is to prevent bit-for-bit copying of protected content to a DVD-RW disc.

•   DVD-RW media will have a unique serial number written in the Narrow Burst Cutting Area (NBCA). An authorized DVD-RW media manufacturer places a unique serial number on each disc. This serial number can be used in conjunction with other protective measures to allow copy protected content to be stored on a DVD-RW disc.

•   A media block key is used to allow a “copy-once” content to be stored on DVD-RW media. The media block key provides an encryption element that allows a CPRM compliant recorder to re-encrypt content that allows one legal copy to be made. A CPRM compliant player will be required to play back the newly encrypted data stored on the DVD-RW disc.

DVD+RW

DVD+RW, which is not an “official” DVD format, has been designed to be compatible with existing DVD-ROM and DVD-Video formats. The DVD+RW format allows both Constant Angular Velocity (CAV) and Constant Linear Velocity (CLV) recording. In CAV recording the disc is rotated at a constant speed. In CLV recording the rotation speed of the disc is varied based on the position of the laser relative to the inner data ring. As the laser moves away from the center of the disc the rotation speed is slowed to maintain a constant write throughput rate. Due to the constant rotation speed of the disc, CAV recording allows for fast random access. Two other benefits of the DVD+RW format are the incorporation of defect management, especially designed for reliability of the data, and quick formatting, enabling instant use of blank discs. DVD+RW includes the following features:

•   Single-sided disc has 4.37 Gb capacity

•   Double-sided disc has 8.75 Gb capacity

•   Uses a bare disc - no cartridge required

•   650 nm laser

•   CLV and CAV recording

•   Write speeds from 1x to 2.4

•   Defect management handled by the drive

•   Quick formatting

•   Uses same 8-16 Modulation and Reed-Solomon Error Correction Code as DVD-ROM

The recording layer of a DVD+RW disc is polycrystalline. When the DVD is recorded, a laser beam selectively heats areas of the phase-change material above the melting temperature (500-700°C), so all the atoms in this area can move rapidly in the liquid state. Then, when cooled sufficiently quickly, the random liquid state is frozen-in and a so-called amorphous state is obtained. If the phase-change layer is heated below the melting temperature but above the crystallization temperature (200°C) for a sufficient time, the atoms revert back to an ordered state, i.e. the crystalline state. The amorphous and crystalline states have different refractive indexes, and can therefore be optically distinguished.

In the DVD+RW system, the amorphous state has a lower reflectance than the crystalline state and, during read out, this produces a signal identical to that of a dual layer DVD-ROM disc. An important feature of the DVD+RW disc is its compatibility with existing DVD-Video and DVD-ROM drives. All physical parameters fit within the DVD-ROM specification. The reflectivity is in the same range as the dual-layer reflectivity specification of a read-only disc and the density is the same as for the single layer specification.

In summary there are three official recordable DVD formats (DVD-R, DVD-RAM and DVD-RW) and one unofficial recordable format (DVD+RW). Each of these formats has their own particular strengths and weaknesses, as shown in Table 2.6.

Table 2.6 Comparison of Writeable DVD formats

Super Audio CD

Philips and Sony have developed an alternative to DVD-Audio, called Super Audio CD that uses a different audio coding method, Direct Stream Digital (DSD) and the use of a hybrid disc format. This hybrid format combines a traditional 650 MB CD-Audio data layer with a 4.37 GB DVD data layer onto a single disc. SACD offers high quality, multi-channel audio, CD compatibility, copy protection and added features. The main features of SACD are:

•   Up to 100kHz bandwidth

•   120 dB dynamic range

•   Full quality for all channels

•   Hybrid disc (CD and DVD)

•   Watermarking and copy protection

•   Text, graphics and video

DSD was chosen as the encoding format because it avoids using PCM, which is a high quality, but uncompressed format. Sony and Philips believe that DSD offers high quality audio with lossless compression, and is more future proof than PCM. Watermarking for copy protection uses pit signal processing (PSP) which known piracy processes can’t copy. SACD also includes a visible watermark. The SACD specification is contained in the Scarlet Book. SACD discs use the same sector size, error correction, modulation, and file system (UDF plus ISO 9660) as DVD discs.

The hybrid CD/DVD disc format allows the same disc to play on existing audio players as well as Super Audio CD players. This is possible by molding the CD-Audio pits on the outside of the otherwise blank DVD substrate and using a semi-reflective layer for the DVD, thus allowing the CD-Audio layer to be read by a conventional CD player.

This means that SACD discs can be played on existing CD players, easing consumer fears of obsolescence. However these DVD/CD hybrid discs are more difficult and therefore more expensive to manufacture than CDs. Since it’s initial product launch in 2000 over 500 titles have been published in the SACD format. Suggested retail prices for most single album SACD titles are $19.98, making them about 33% more expensive than CD-Audio titles. SACD players were priced around $5,000 at product launch, but have come down to about $500 when this book was published, in 2001.

It remains to be seen if the SACD format can compete effectively with the DVD-Audio formats. Some manufacturers will include both SACD and DVD-Audio playback features on their new models, offering a Universal player that supports DVD-Video, DVD-Audio and SACD. It is also possible that consumers will prefer DVD-Audio to SACD, or SACD over DVD-Audio, and thus the less popular format will be relegated to the lengthy list of new consumer home entertainment formats that never achieved mass-market status.