DVD-Audio Developer's Summary
Programmers and others developing DVD-Audio products should know the specific definitions of terms, file structures, and the interrelationships of file types. This section provides such overview information. Part 4 of the DVD specification describes the DVD-Audio format. It uses all the specifications from Part 1 and Part 2, and many of the specifications from Part 3. In particular, there are strong parallels between DVD-Video and DVD-Audio in terms of file management for navigation and presentation data. For example, instead of a Video Manager and Video Title Sets, an Audio Manager and Audio Title Sets are used. Likewise, many of the same navigation features are used.
As noted, the complexity in the DVD standards is not in the coding itself (UDF, MPEG-2, and AC-3 are complex unto themselves). The DVD standards focus on how data is organized, and how the player should function. However, in some ways, DVD-Audio is somewhat more complex than DVD-Video. Whereas DVD-Video uses one kind of video coding (MPEG-2), DVD-Audio allows for many kinds of coding, with one to six channels. Parenthetically, it is worth noting that the terminology used in DVD-Audio differs from that used in DVD-Video. For example, in DVD-Video we refer to Title, Program, and Cell; whereas, in DVD-Audio we refer to Group, Track, and Index, respectively. DVD-Audio provides stereo and multichannel playback.
A Volume space includes a DVD-Volume zone and DVD Audio zones as well as DVD-Video zones and DVD-Other zones (see FIG. 11B). The DVD-Volume zone complies with the UDF Bridge structure defined in Part 2. The DVD Video zone and DVD-Other zone are defined in Part 3. A DVD-Audio zone is an area to record the audio contents in a volume of a DVD-Audio disc. It contains one Audio Manager (AMG) and one or more (maximum of 99) Audio Title Sets (ATSs). The AMG is the table for all contents in the DVD-Audio zone (and DVD-Video zone if present) and Navigation data. The AMG is composed of Audio Manager Information (AMGI ), optional Video Object Set for AMG Menu (AMGM VOBS) and a backup of AMGI . ATT is a general name given to Audio Only Title (AOTT) and Audio with Video Title (AVTT). An AOTT title has no video data except for still pictures and is defined in the PGCI in the ATS. An AVTT title (otherwise known as AV) has video data and is defined in the PGCI in the VTS. AOTTs are playable by Audio players and Universal players, and AVTTs are playable by Universal players. The DVD-Audio file structure is the same as that used in DVD-Video (see FIG. 15).
The Audio Title Set defines the Audio Only Titles. The ATS contains Audio Objects (AOBs) and can contain visual menus. Generally, one AOB comprises one track on the disc. Further, an AOB can have two streams, such as stereo and multichannel. (AVTTs are defined in the Video Title Set with links from the ATS). An AOB track can also optionally contain still images, stored in Audio Still Video (ASV) files. There are two kinds of ATSs. One kind is composed of Audio Title Set Information (ATSI ), Audio Object Set for Audio Only Title (AOTT AOBS), and a backup of ATSI . The other is composed of ATSI and its backup.
The Presentation hierarchical structure is an Album (one disc side), a Group, an Audio Title (ATT), a Track, and Index. ATT is not accessible by the user. A Group contains one or more Audio Titles. There are several types of ATTs.
AOTT is playable by all Audio players. AVTT is playable by a Video Capable Audio player.
Both an AOTT and AVTT contain a Program Chain (PGC). A Track is a Program (PG) defined in the PGC of ATS. The attribute is the definition of sampling frequency, quantization word length, and so on. An Index is a cell defined for audio contents in the PGC. An index may consist of two or more cells.
Presentation of contents starts from the track (or index) selected by the user. This is the same as the playback of PGC as defined in the ATS. Video data including sub picture in video contents and still picture in audio contents are played by a Video Capable Audio player. Some types of Real-Time information can be recorded within the audio contents, if desired. Real-Time Text Data (RTXTDT) contains text data such as lyrics, and explanations of contents. One Page consists of 4 lines with 30 characters per line or 2 lines with 15 characters per line. Text is presented onscreen one page at a time. Eight languages are available. Two kinds of audio data (such as multichannel or not, or PCM or another coding) may be defined in an ATT; this is also known as a selection. (For AOTTs, they are defined as the PGC block, and for AVTTs, they are defined as two streams of audio in a Video Object.)
The Visual Menu is the menu for the AMG. Presentation of the Visual Menu is the same as playback of one or more PGCs that are defined for the AMG Menu. It is played back by Video Capable Audio players but ignored by Audio-Only players which use a simpler SAPP (Simple Audio Play Pointer) feature.
The AMG is the table of contents for all ATSs that exist in the DVD-Audio zone, and all VTSs for audio titles that exist in the DVD-Video zone. The AMG contains Audio Manager Information that contains Navigation data for every audio title and its backup. It may also contain Video Objects used for the Visual Menu. The AMGI is composed of the Audio Manager Information Management Table, Audio Title Search Pointer Table, Audio Only Title Search Pointer Table, Audio Manager Menu PGCI Unit Table, and optional Audio Text Data Manager. The AMGI describes information in the AUDIO_TS directory. The Audio Manager Information Management Table (AMGI_MAT) is a table that describes the size of the AMG and AMGI , starting addresses of information in the AMG and other attribute information such as number of volumes, disc side where a volume is recorded, video display mode, aspect ratio, audio coding mode, and sampling frequency. The Audio Title Search Pointer Table is a table with search information (starting and ending addresses) for Audio Titles and is used by a Video Capable Audio player.
The Audio Only Title Search Pointer Table is a table that contains search information (addresses) of AOTTs and is used by Audio-Only players; this is part of the SAPP feature. The Audio Manager Menu PGCI Unit Table is a table that describes the audio menu. The optional Audio Text Data Manager contains information such as album, group, and track names.
The Video Object for Audio Manager Menu (AMGM_VOB) contains Presentation data (video, audio, and sub-picture data) and some of the Navigation data (PCI and DSI ). The AMGM_VOB is the same as the Video Object, with the same contents, same pack structure, and same data transfer rate. The Presentation data is essentially the same as in Part 3. Its PCI and DSI data are essentially the same, with some added restrictions. The AMGM_VOB contains the ISRC code.
The Audio Title Set defines the Audio Only Titles that are defined by the Navigation data and the Audio Objects in the ATS, or by the Navigation data in the ATS and the audio part of Video Objects in the VTS. The ATSs are recorded in the DVD-Audio zone along with the Audio Manager, and the VTSs to be used for the audio title are recorded in the DVD-Video zone along with the Video Manager. The ATSs contain Audio Title Set Information (ATSI ), an Audio Object Set for Audio Only Title (AOTT_AOBS), and a backup. The ATSI contains the Navigation data needed to play back every ATT in the ATS and provides information to support User Operation. ATSI contains the Audio Title Set Information Management Table (ATSI_MAT), and Audio Title Set PCI Table (ATS_PGCIT). The AOTT_AOBS is a collection of Audio Objects for Audio Only Title that contains Presentation data such as audio data, optional still picture data, and some kinds of optional Real-Time Information (RTI ).
The Audio Title Set Information Management Table (ATSI_MAT) describes the size and starting addresses of ATS and ATSI , as well as attributes. It describes the audio coding method, downmix mode, quantization word length, and sampling frequency of two channel groups. The ATSI_MAT also describes the coefficients to mix down the audio data from multichannel to two-channel. An area containing 16 coefficient tables is provided. The ATS also contains Audio Title Set PCI (ATS_PGCIT), which is the Navigation data to control the presentation of the Audio Title Set Program Chain (ATS_PGC). This information describes the addresses of data, as well as the presentation order of programs and cells.
The Audio Object for Audio Only Title (AOTT_AOB) contains the Presentation data that are audio data, Real Time Information (RTI ) data and still picture data. The AOTT_ AOB is an elementary program stream described by the ISO/IEC 13818-1 standard. The AOTT_AOB uses three types of packs: Audio pack, Real-Time Information pack, and Still Picture pack. The maximum length of a pack is 2048 bytes. The maximum transfer rate of the audio stream is 9.6 Mbps. The maximum video transfer rate for still pictures is 9.8 Mbps.
The AOTT_AOBS Structure is a collection of AOTT_AOB files whose attributes are the same or different up to eight. It is composed of one or more cells that are made up of packs. The pack structure of the AOTT_AOB follows the general 2048-byte DVD pack layout (see Fig. 10) with 14 bytes of pack header and 2034 bytes of packets. In many ways, the AOTT_AOB is the core of a DVD-Audio disc. It contains the Presentation data (mainly audio). It adheres to the ISO/IEC 13818-1 standard (the MPEG-2 stream layer specification). As noted, 13818-1 compliance does not mean that audio is coded as MPEG-2. Rather, the format of the bitstream itself adheres to MPEG-2. Linear PCM data is held in A_PKT packets. As in Part 3, a Pack is a header, followed by packets. A Pack adheres to ISO/IEC 13818-1; a Packet is the elementary data stream following the header. An AOTT_AOB Audio pack (A_PCK) has up to 2013 bytes of user data. A LPCM packet (A_PKT) comprises a packet header, the private header, and the audio data. The private header has information such as ISRC, audio emphasis, downmix code, quantization word length, sampling frequency, multichannel type, and dynamic range control.
An AOTT_AOB Real-Time Information pack (RTI_PCK) contains up to 2015 user bytes. An RTI packet (RTI_PKT) comprises a packet header, the private header and RTI data. RTI data (such as real-time text, and ISRC) is used synchronously with audio data. An AOTT_AOB Still Picture pack (SPCT_PCK) contains up to 2025 user bytes. A Still Picture pack (SPCT_PKT) comprises a packet header and video data for the still picture. The still picture is one GOP (with one I -frame), which complies with ISO/IEC 13818-2 (MEG-2 video). The following audio data is mandatory in an AOTT: PCM of one or two audio channels or PCM for three to six audio channels with downmix coefficients, or PCM data of three to six channels without downmix coefficients.
(In some cases, an Audio player may not play back this PCM data.) Other types of audio data (such as compressed and lossless compressed) may be contained in an AOTT_AOB as an option. The audio stream is divided into packs of 2048 bytes.
The general DVD-Audio specification for linear PCM describes the number of channels, sampling frequency, quantization, and emphasis. Total maximum bit rate is 9.6 Mbps. Coding is two's complement. When there are three or more audio channels, they are classified into two groups:
Channel Group 1 (CG1) and Channel Group 2 (CG2). The data in each group may use different sampling frequencies and word lengths. The word length is identical in every channel of the same CG, but each CG may have different word lengths (16, 20, 24). Sampling frequencies of 176.4 kHz and 192 kHz are only used when there are two channels (L and R) or less. CG1 generally defines stereo and front channels, and CG2 defines rear channels.
When an ATS has AOTT_AOBS, the structure of CG1 and CG2 and the relation between the audio channel and audio signal is described in the ATS Multi Channel Type area (it must be Type 1) according to an Assignment for Audio Object table. When an ATS has no AOTT_AOBS, the relation between the audio channel and audio signal and the number of audio channels is described in the ATS Multi Channel Type area (it must be Type 1) according to an Assignment for Video Object table. The channels supported are: Left Front, Right Front, Center, Low Frequency Effects, Surround, Left Surround, and Right Surround.
The downmix procedure outputs channel signals from input signals that have more channels than outputs. Mixing phase and mixing coefficients are used to produce a two channel output from six-channel input signals. In this way, it is not necessary to place a separate two-channel mix on a multichannel disc. Each gain controller is programmed with a coefficient value. It also manages the phase (polarity) of the signal. The downmix coefficient (DM_COEFT) is defined in the disc ATS and SAPP lead-in area. It is used by the player to control the downmix procedure. The decimal coefficient value is 0 to 255. It is calculated according to a formula for a specific gain control curve.
The video contents of an Audio with Video Title (AVTT) (also known as AV) are recorded in the DVD-Video zone (one with one VMG and one or more VTSs). VMG is not used by Audio players but may be used by DVD-Video players, which cannot recognize AMG. The inclusion of a VMG allows DVD-Video players to play video tracks on a DVD-Audio disc that may include PCM or Dolby Digital content. VTS is used to define the AVTT of a DVD-Audio disc. Titles defined by VTS are pointed to by the Audio Manager. Various restrictions apply to the VMG of DVD Audio; for example, a DVD-Audio disc has no region management or parental management. Restrictions also apply to the VTS of DVD-Audio.
DVD-Audio provides a degree of navigation interactivity, such as branching. However, these features are operational only for Video Capable Audio players.
Audio-Only players may ignore these features. The navigation features for DVD-Audio are a subset of those specified for DVD-Video. Some special navigation features are added to the reserved areas of the Part 3 specification to support specific audio needs. Part 4 navigation parameters are classified as General Parameters (GPRM) and System Parameters (SPRM).
There are sixteen 16-bit GPRMs (such as go to, jump, link, and compare) to memorize the user's operational history and modify operation of Video Capable Audio players. In addition, there are twenty-four 16-bit SPRMs (such as audio selection number, sub-picture stream number, highlighted button number, audio player configuration, and track number) for player settings.
The Simple Audio Play Pointer (SAPP) provides TOC like data for simple Audio-Only players that may use a simple alphanumeric readout instead of a video display.
The SAPPT is a table (a subset of navigation) recorded in the control data in the disc lead-in area and consists of one or more SAPPs. Each SAPP is information for the track presented by a simple Audio player that plays back only PCM not using the Program Chain defined in the Audio Title Set. Every audio program defined in the ATS_PGC that satisfies certain conditions is a SAPP. The conditions are: audio coding mode of PCM, and stereo or monaural output. A SAPPT specifically describes the number of SAPPs and the end address of the SAPPT. The size of an SAPPT must be less than 16,384 bytes. A SAPP describes address information and playback information for a track such as track number, start time of the first audio cell, playback time, track attributes such as word length and sampling frequency of CG, downmix coefficient, and end address.
At the hardware player, packs in the program stream are received from the disc and transferred to the appropriate decoder. A buffer is used to ensure continuous supply of data to the decoders. In a Video Capable Audio player, DSI data (navigation used to search and seamlessly play back branching) in AVTT is treated separately. The audio stream may include the Audio Gap that is the discontinuous period of the audio stream during the presentation of a Still Picture. During the Audio Gap, the player's audio output is muted.
Alternative DVD Formats
In addition to the DVD-Video format defined in Book B and the DVD-Audio format defined in Book C, the DVD family includes DVD-ROM (Read-Only Memory) defined in Book A, DVD-R (Recordable) defined in Book D, DVD-RAM (Random-Access Memory) defined in Book E, and DVD RW (ReWritable) defined in Book F. DVD Books A, B, and C use a UDF Bridge file format (M-UDF + ISO 9660) and Books D, E, and F use the UDF format. The DVD-ROM, DVD-R, DVD-RAM, DVD-RW, and DVD + RW formats are employed as computer peripherals, in professional authoring environments, or in consumer applications.
Single-sided and double-sided recordable discs are available. DVD-ROM is a read-only format, DVD-R is a write-once format, while the others are rewritable. The specifications for DVD-R, DVD-RW, and DVD-RAM are supported by the DVD Forum (www.dvdforum.org). The DVD + R and DVD + RW specifications are supported by the DVD + RW Alliance (www.dvdrw.com). The family of recordable DVD formats is summarized in Table 10.
Table 10 Specifications for recordable DVD disc formats (4.7-Gbyte capacity).
The recordable DVD formats can store diverse types of data; however, several specifications for specific data types have been defined: DVD Video Recording (DVD VR), DVD Audio Recording (DVD-AR), and DVD Stream Recording (DVD-SR). The DVD-VR recording format is borrowed from DVD-Video. DVD-VR recorders allow real time recording of video, stereo PCM audio, as well as still pictures, and users can create custom play lists. A new VOBU map, located in the VOBI area, stores time stamps; when a recording is completed, users can create menus to easily access programs. DVD-AR is derived from the DVD-Video and DVD-Audio formats; it supports real-time audio recording, as well as still pictures and text. The various DVD-Audio sampling frequencies are supported as is PCM, Dolby Digital, and MPEG formats. Users can create custom play lists to access disc contents. The DVD SR format is derived from the DVD-Video format. It acts as a bit bucket to allow recording of streaming data from digital sources such as camcorders, cable boxes, and satellite receivers. An IEEE 1394 interface can be used.
DVD-ROM
At their base level, all DVD discs are DVD-ROM (Read Only Memory) discs. That is, all DVD discs use the UDF format. Different DVD applications, such as DVD-Video, place specialized material in a specific place, such as the DVD-Video zone. Content contained in the DVD-Other zone may be quite varied, and DVD-ROM uses that opportunity for open-ended storage. In that respect, DVD ROM is a large capacity bit bucket formatted as UDF.
DVD-ROM discs are playback-only media used for high capacity storage of data, software, games, and so on.
DVD-ROM drives are connected to personal computers and function much like CD-ROM drives. With appropriate software, DVD-ROM drives can play DVD-Video and DVD-Audio discs. As with other DVD players, to play back CD-R discs at a 780-nm wavelength and DVD discs at a 635-nm or 650-nm wavelength, DVD-ROM drives must use pickups with dual lasers and other appropriate optical design. DVD-ROM drives support DVD-Video regional coding as well as CSS copy protection. The various recordable formats are not mutually compatible, and there is variability in disc-to-drive compatibility.
DVD-R and DVD+R
DVD-R (Recordable) discs, like CD-R, offer write-once capability to permanently record data. The DVD-R(A) Authoring format is often used for professional authoring and testing of DVD titles. The DVD-R(G) General format is used for business and consumer applications. Because DVD-R(A) uses a 635-nm laser for writing and DVD-R(G) uses a 650-nm laser, the two media are not write incompatible. However, discs are playable in both types of drives. DVD-R(A) has a Cutting Master Format (CMF) functionality that allows a Disc Description Protocol (DDP) file to be written in the lead-in area for mastering applications. Replication plants can use these discs directly. DVD-R(G) discs include measures to limit piracy; for example, some decryption keys are blanked out. It is thus impossible to copy CSS-encrypted data to a disc. Also, DDP data cannot be written to DVD-R(G) discs.
FIG. 21 DVD-R discs contain a dye recording layer backed by a reflective
metal and protective layer, all sandwiched between two substrates. DVD-R discs
comprise two substrates bonded together.
A single-sided disc uses one pregrooved substrate bonded to one pregrooved dummy substrate. The recording side of a single-sided disc comprises a polycarbonate substrate, organic dye recording layer, reflective layer, and protective lacquer overcoat, as shown in FIG. 21. The dummy side comprises a substrate, cosmetic reflective layer, and protective lacquer overcoat.
The CLV wobbled pregroove generates a carrier signal used for motor control, tracking, and focus. However, whereas CD-R discs use a physical frequency modulation of the pregroove carrier signal to encode the Absolute Time In Pregroove address and prerecorded signal, DVD R discs use pits and land (known as land pre-pits) molded into land areas between grooves. Placed at the beginning of each sector, the pre-pits contain addressing, laser writing power, and synchronization information. The reading laser tracks the pregroove, but the light shines on the pre pits peripherally to create a secondary signal that can be extracted from the main signal. As with CD-R, DVD-R uses a pulsed laser to create marks in the organic dye, controlling the duration and intensity of the laser bursts.
However, whereas the CD-R write strategy typically simply turns the laser on and off, during DVD-R writing the laser is modulated between a recording and reading bias power to create a multi-pulse train to write one mark. This efficiently controls heat, and creates smaller and more accurate marks. Disc manufacturers can optionally place a write strategy code in the lead-in pre-pits to modify the player's write strategy. Reflectivity for DVD-R and DVD + R discs is about 45 to 85%.
DVD-R discs contain a power calibration area (PCA) for testing laser power. A recording management area (RMA) stores calibration information, disc contents and recording locations, remaining capacity information, and recorder and disc identifiers for copy protection. Recorders perform an optimum power calibration (OPC) procedure to determine the correct laser writing power for particular discs. The PCA can hold 7088 different calibrations, and the RMA can hold OPC information for as many as four different recorders. The remainder of the disc comprises the Information Area. It contains the lead-in, data recordable area, and lead-out. The lead-in contains information on disc format, specification version, physical size and structure, minimum readout rate, recording density, and pointers to the location of the data recordable area where user data is recorded. The lead-out marks the end of the recording area.
DVD-R discs can use the same reference velocity and track pitch as molded discs to achieve the same unformatted storage capacity; user capacity of a "4.7 Gbyte" Version 2.0 disc holds 4.7 billion bytes, or 4.35 Gbytes of user data per side. A cyanine, phthalocyanine or azo dye recording layer may be used, with a 635-nm or 650-nm laser. Both sequential (disc-at-once) and incremental writing can be performed. Once recorded, DVD-R discs are highly compatible and can be played in many DVD-ROM, DVD-Video, and DVD-Audio players.
Longevity of a recorded disc is similar to that of a CD-R disc; estimates range from 50 to 300 years. On the other hand, as with most recordable media, the shelf life of unrecorded discs might be only 10 years. Single-sided, dual-layer discs (using the same physical parameters as DVD-ROM discs) hold 8.5 billion bytes. Most drives can read both layers; however, a dual-layer (DL) recorder is needed to write to the second layer.
FIG. 22 DVD-RW discs contain a phase-change recording layer backed by
a reflective metal layer. The recording layer is sandwiched between two dielectric
layers to control thermal properties. Two substrates are bonded together. DVD
+ RW discs use the same physical construction.
The DVD + R format is another write-once format. It is not officially a part of the DVD specification written by the DVD Forum. It uses a dye recording layer and CLV rotation. Discs are available in a 4.7- and 8.5-Gbyte (DL) capacity. DVD + R discs are highly compatible and can be played in many DVD-ROM, DVD-Video, and DVD-Audio players. However, DL recorders are needed to record to the added layer.
DVD-RW and DVD + RW
DVD-RW (ReWritable) allows rewriting of data; the specification is essentially an extension to the DVD-R format. It is similar to the CD-RW format. DVD-RW is used for both professional authoring and consumer applications.
Discs use a phase-change recording mechanism and a multilayer disc structure shown in FIG. 22. The recording layer may use a silver, indium, antimony, and tellurium compounded layer, and perhaps 1000 read/erase cycles are possible. Unlike dye-polymer technologies, phase change recording is not wavelength-specific. Reflectivity for DVD-RW discs (and other phase-change discs) is about 18 to 30%. The disc uses a wobbled pregroove, and pre pits with addressing and synchronization information. Data is recorded inside the pregroove, and in relatively large blocks. As with DVD-R, there are PMA and RMA zones. A DVD-RW disc may hold 4.37 Gbytes per side. DVD-RW uses CLV rotation; thus, it is particularly used for sequential writing, as in mastering applications. Because it has less robust error protection and a relatively small number of rewrite cycles, DVD-RW is not intended for general purpose data storage and distribution. Although not required, some players use a protective disc caddy. DVD RW was previously known as DVD-R/W. DVD-RW discs are highly compatible and can be played in many DVD drives. As with other recordable DVD media, the longevity of a DVD-RW disc might be as long as 100 years.
DVD + RW is another rewritable format. It is not officially a part of the DVD specification written by the DVD Forum.
It uses phase-change media and a wobbled pregroove; the frequency modulation in the wobble provides address in pregroove (ADIP) addressing information. Data is written inside the groove and there is no pre-embossed addressing data. Disc layer construction is the same as in the DVD RW format (see FIG. 22). Data is written and read in relatively large blocks compared to DVD-RAM. CLV or CAV rotation is allowed for recording, for either sequential data transfer (as in audio/video recording) or faster random access (as in computer data), respectively. Optional defect management features, similar to those found on DVD RAM, are available. One thousand rewrite cycles are possible. Nominal capacity of a CLV disc is 4.7 Gbytes, and a double-layer (DL) disc holds 8.5 Gbytes. DVD + RW discs recorded with CLV can be played in some DVD drives.
DVD-RAM
DVD-RAM (Random-Access Memory) is a rewritable format. It uses a phase-change recording mechanism and a wobbled land and groove disc design. Using this structure, data may be recorded on both planar surfaces of the groove and land, as shown in the upper part of Fig. 23. This technique doubles disc capacity, but deep grooves with steep walls are needed to avoid crosstalk interference between adjacent data. In addition, servos must be employed to switch the pickup's focus between the groove and land area on each revolution. In addition, the tracking signal is inverted when the switch occurs.
However, designers contend that the wider groove pitch provided by the groove/land recording technique allows easier tracking and faster recovery from physical shock.
Discs also contain pre-embossed pit areas (for every 2k sector) to provide addressing header information, as shown in the lower part of FIG. 23. A zoned constant linear velocity (ZCLV) rotational control is used. This technique divides the disc surface into a number of zones, each with a different CLV, but with the same CAV within each zone. There are a total of 35 recording zones across a 120-mm Version 2.0 disc. Successive zones contain more sectors, with 39,200 sectors in the first zone and 105,728 sectors in the last zone. The ZCLV feature enables DVD-RAM to be used as a true random-access, non-sequential medium. Thus, DVD-RAM is well-suited for writing and reading chores done from computer drives.
FIG. 23 DVD-RAM discs use a land and groove recording technique. As seen
in the upper portion of the figure, phase change data may be placed on planar
surfaces of both the wobbled pregroove and land. As shown in the lower part
of the figure, rewritable areas are separated by pre-embossed sector headers
holding addressing information. (Parker, 1998)
DVD-RAM provides advanced error correction and defect management features. In the latter feature, defective sectors are identified during manufacture or formatting (or reformatting) and pre-allocated spare sectors can substitute for them. To reduce wear and tear on specific portions of the disc that are repeatedly written to, the system automatically shifts data placement on the disc surface.
DVD-RAM Version 2.0 discs marketed with capacities of 4.7 and 9.4 billion bytes hold 4.37 Gbytes (single-sided) and 8.74 Gbytes (double-sided), respectively. A recording rate of 22.16 Mbps is possible. A disc allows perhaps 100,000 rewrite cycles, and offers a high degree of stability for archiving integrity. DVD-RAM is designed primarily for professional DVD authoring and other post-production work but some consumers use DVD-RAM discs. DVD RAM discs may be played in many DVD-ROM drives and in some DVD-Video and DVD-Audio players. Higher capacity discs are usually held in protective cartridges that require slot-loading drives. Some discs can be removed from their cartridges for playback in tray-loading drives.
Because of its relatively unique design features it is not as compatible as other recordable DVD formats.
DVD Multi is not a disc format; rather, it is a specification that promotes compatibility within the DVD family. A read-only drive denoted as DVD Multi is capable of reading DVD-ROM, DVD-R, DVD-RW, and DVD-RAM media. Likewise, a writeable drive denoted as a DVD Multi can read all of these media, and can also write on DVD-R, DVD-RW, and DVD-RAM media.
DVD Content Protection
The intellectual property potentially stored on DVD discs has a monetary value that is almost incalculable.
Prerecorded formats such as DVD-Video and DVD-Audio provide content owners with the option of securing and monitoring their data in a variety of ways including encryption and watermarking. Likewise, recordable media such as DVD-R, DVD-RW, DVD-RAM, and DVD + RW can employ content protection to prohibit or limit copying. A delicate balance is required so that while content is secured, the user is not unnecessarily inconvenienced; these requirements are mutually contradictory in any content protection system. A number of copy-protection mechanisms, summarized in Table 11, are optionally available to content owners.
Table 11 Summary of copy-protection systems.
DVD-Video Copy Protection
A group known as the 4C entity, comprising Intel, IBM, Matsushita, and Toshiba, developed the Content Protection System Architecture (CPSA) that encompasses security issues for DVD formats. In all, eight different security features are used in DVD formats.
In cooperation with 4C, the Copy Protection Technical Working Group (CPTWG) representing 60 companies and interest groups developed the Content Scrambling System (CSS) copy-protection system that is standard in DVD Video discs. The CPTWG also established an independent, nonprofit group to oversee nominal cost based licensing of the CSS technology. Data encryption is used so that content is self-protecting, but use of the technology is voluntary; discs can be distributed with or without copy protection. Likewise, manufacturers could offer a player without decryption hardware; however, it could only play non-encrypted discs. To obtain the algorithms and keys needed to decrypt data in their players, manufacturers must first obtain a DVD license. The data stream is flagged so computer programs can properly interpret the encryption. A Matsushita proposal is the basis for the CSS system. With CSS, content is self-protecting; that is, content cannot be digitally copied because software keys needed to decrypt the data are missing in any copy.
Although it is a different technology, regional coding must be implemented in any CSS device.
When encrypted data is decoded in software (as opposed to a dedicated hardware chip) care must be taken so that excessive demands are not placed on the microprocessor. CSS is designed to minimize the burden, allowing efficient decryption (descrambling) without compromising integrity. Moreover, CSS limits the processor overhead required to perform decryption. In the variable-rate MPEG-2 video coding algorithm, video frames are stored as data sectors. There are 2048 bytes/sector. At a fast data rate of 10 Mbps, there might be 600 sectors/second or 20 sectors/frame; at a slow data ate of 2 Mbps, there might be 120 sectors/second or 4 sectors/frame. Instead of encrypting all video sectors, the CPTWG sets an upper limit (and lower limit) on the rate of sectors encrypted by CSS. For example, 10 or 15% of sectors might be encrypted. Even with a low rate, the picture will be unviewable, but the limit minimizes microprocessor overhead.
The proprietary CSS system encrypts data during encoding and then uses authentication to verify that the player's decoder is authorized to decrypt the data.
Moreover, communication within the system is encrypted to maintain security over keys. Most DVD-Video players have dedicated authentication hardware. CSS decoding can be performed in hardware or software and every decoder has a 40-bit player key used to decrypt a disc key, and uses the esult with the title key to decrypt the movie contents.
CSS features two copy-protection methods. The first, he "Content Scrambled DVD" method, is designed for DVD-Video players. Sectors containing audio and video signals are encrypted; navigation data in sector headers is not encrypted. Content providers must select two encryption keys-one disc key and one title key-jointly used to encrypt the data prior to storage on a DVD-Video disc. The title key is placed in a disc sector header, and the disc key is concealed in a control area of a disc that cannot be read by a DVD-ROM drive unless instructed by authentication commands. Each licensed manufacturer is assigned one of 400 unique player keys; all 400 keys are stored in every disc using CSS encryption. If a license lapses, that manufacturer's key can be omitted from future disc pressings.
The DVD-Video player's hardware decrypting chip is placed in the bitstream between the source data, and the internal Dolby Digital and MPEG-2 decoders. The person viewing the program via an analog output will not know that decryption is taking place. However, if the player contains a digital output, that output will be tapped off prior to decrypting. Copies made from the output digital stream cannot be decrypted because any subsequent decoders will not be able to retrieve the encryption keys and use them to decrypt the data.
The second, the "Bus Authentication and Encryption" method, is designed for use in the computer environment, where encrypted 128-bit keys must be transmitted from a DVD-Video disc across a computer bus to decryption software or hardware. An authentication key is used in addition to the disc and title keys, and each key is checked by elaborately sending data between the disc and the decrypter. This method is more sophisticated because during playback it performs additional encryption on the keys themselves.
In addition, CSS requires that an analog protection system (APS) be employed. Macrovision copy protection, similar to that used in set-top boxes and video networks (which in turn is similar to that protection used in analog videocassettes) is typically used. The Macrovision system can prevent digital-to-analog copying, for example, attempting to use the analog output from a DVD-Video player to make a VHS tape copy. This system uses automatic gain control (AGC) and Colorstripe methods.
The AGC portion is virtually identical to that used in prerecorded videocassettes; bipolar pulse signals are added to the video vertical blanking signal causing a VCR to record a weak, noisy, and unstable signal. Because the AGC of a television works quite differently from the AGC of a VCR, VCR playback is disrupted, whereas television display is not. The Colorstripe method is similar to that used in digital set-top boxes; it modulates the phase of the colorburst signal in a rapid, controlled manner, creating horizontal stripes in a copy. A recording VCR recognizes the colorburst phase changes as timebase errors and acts to correct them, thus inducing color errors in the picture. An unauthorized copy shows stripes of color, distortion, rolling, a black and white picture, and dark/light cycling. Colorburst is not present in a component video signal. Use of Macrovision is optional and per-disc licensing fees are paid. The disc identifies its Macrovision protection to the player. A player or drive that does not contain APS would not play DVD-Video discs encrypted with CSS. Likewise, video cards may use APS.
CSS technology is used primarily by the motion picture industry (but its use on a disc is optional). Many computer software providers do not use CSS, even for their audio/video content. Importantly, CSS does not protect other types of data such as software programs.
Manufacturers who want to accommodate playback of CSS-coded titles may apply for a license and place CSS decoders in their products. Products without CSS decoding would not play back CSS-coded titles. For example, a DVD-ROM drive might not contain a CSS descrambler; the drive could be used to play back non scrambled data, but could not be used to watch scrambled movies on a computer. Some professional pirates use DVD replication lines to produce bit-for-bit accurate DVD Video discs-complete with CSS encryption. Another piracy method rips a DVD-Video disc into its component video and audio contents and re-codes them to Video CD.
Both methods violate copyright law. The Data Hiding Sub Group (DHSG) of the CPTWG is charged with the development and evaluation of watermarks. Encryption and water-marking are also discussed in Section 15.
DVD-Audio Copy Protection
To protect against unauthorized copying, the DVD-Audio format uses an optional CPPM content protection framework employing encryption and embedded watermark technology. Copy-protected DVD-Audio discs can only be played on licensed players. The Content Protection for Prerecorded Media (CPPM) was devised in March 1999, by IBM, Intel, Matsushita, and Toshiba in conjunction with music industry companies such as BMG, EMI , Sony Music, Universal Music Group, and Warner Music Group. WG-9 is charged with copy-protection issues. CPPM is similar in intent to the CSS system used in the DVD-Video format and CPPM uses the same authentication measures as CSS. However, CPPM's protection is more sophisticated.
The CPPM encryption code is stronger than that used in the DVD-Video format. A secret album identifier is placed in a control area of the disc that cannot be read by recordable drives, and so cannot be copied to a blank media. Each player or drive has 16 device keys. A media key block is placed on every disc, and the player's device keys interact with the media key block to generate a media key. It is used with the album identifier to decrypt encrypted portions of the disc contents. In the event of hacking, there is capability to revoke, expire, or recover encryption keys.
The CPPM content protection system provides a number of options to content providers of prerecorded media; for example, consumers can make one CD-quality digital copy, per recorder, of the original content. Related content such as supporting text and images is not copied.
Content providers can also allow additional copies at various quality levels, up to and including the full quality of the DVD-Audio multichannel original. The encryption used in DVD-Audio can allow two-channel CD-quality, real-time copying along the IEC-958 interface. It also allows both two-channel and multichannel, CD-quality and higher quality, high speed copying along the IEEE 1394 interface.
The recorder receives ISRC data that identifies the original recording along with copy permission information describing, for example, how many copies are permitted.
The CPPM watermark is designed to identify content through unencrypted digital (and analog) links. It is not used in high-speed encrypted links and instead verifies copy status of unencrypted signals. The watermark is embedded in the audio signal and is robust over analog and data compressed transmission links. The watermark operates similarly to SCMS in the digital domain, but it operates in the analog domain or unencrypted digital domain. A copy permit is the default status; when a copy is made, the embedded watermark signal is updated to mark the copy as a second-generation source. Watermark-compliant recorders will check this mark prior to recording. The watermark can also identify the manufacturer, artist, copyright holder, and other characteristics. The encryption and watermarking technologies are independent; for example, watermarking is optional in encrypted discs.
Content Protection for Recordable Media
Recordable media are protected by the Content Protection for Recordable Media (CPRM) protocol. CPRM links content to the media it is recorded to, so that the recording is playable but copies of the recording are not. CPRM is similar to the CPPM system used specifically for the DVD Audio format. All blank DVD media have a 64-bit media identifier placed in the burst cutting area at the time of manufacture that uniquely identifies each disc. With CPRM, when protected content is recorded to the disc, the media identifier is used to encrypt a title key, which in turn encrypts content. When the disk is played, the media identifier is again used along with other keys to decrypt a title key, which in turn is used to decode the contents. If the content is moved to another disc, its media identifier will not correctly decode the content. Only audio/video sectors are encrypted; navigation and other data is not encrypted.
The Copy Generation Management System (CGMS) controls the copying of digital and analog video signals.
Discs can specify whether any copying is permitted; this is conveyed in data in the output analog and digital signal and interpreted by recorders. Copy instructions in analog signals are placed in the XDS section of the NTSC signal, and in digital signals it is conveyed via DTCP and HDCP protocols. Copy control information (CCI ) includes no copies, one copy, and unlimited copies. When one copy is permitted, the second-generation copy then contains a no copy instruction; however, multiple copies may be made from the original copy. When a disc carries CSS, CPPM, or CPRM, then a "no copy" condition is assumed.
Furthermore, when copying to unprotected media such as CD-R, DVD-Audio limits authorized copies to no more than two channels, 48 kHz and 16 bits.
Secure Digital Transmission
Many applications require a secure link between two devices, such as a computer video card and a display. Two principal systems have been developed. DVD data can be conveyed along these paths, but the disc itself does not participate; the player and display perform the necessary operations independent of the disc contents. The High Band-width Digital Content Protection (HDCP) system defines a secure digital interface for players and displays designed according to the Digital Visual Interface (DVI ) specification. DVI can support transmission at 4.95 Gbps; this provides 1600 × 1200 resolution that encompasses HDTV formats. Twin links can support even higher resolution. HDCP for DVI makes DVI a secure interface.
Connected devices, such as a video display card and a monitor, exchange keys to authenticate the devices; the system uses forty 56-bit device keys and 40-bit key selection. Data is encrypted at the transmitting device and decrypted at the receiving device. If the receiving device is not HDCP equipped, the transmitting device may send a lower resolution version of the content. HDCP was proposed by Intel and ratified by the Digital Display Working Group in 1998.
The Digital Transmission Content Protection (DTCP) system provides secure transmission over bidirectional digital lines such as the IEEE 1394 bus. For example, a DVD player could be digitally and securely connected to an LCD display, and DTCP would resist unauthorized copying by another connected device. DTCP is described in Section 14 in the context of IEEE 1394.
DVD Watermarking
Watermarking can be used to intertwine data into DVD contents so that the watermark can later be retrieved to identify the contents on the disc. Furthermore, most watermarks resist tampering or removal. Watermarking does not prevent copying; it merely identifies the content. In some cases, a fragile watermark is used; analog copying degrades the watermark and thus identifies the content as a copy. A watermark is only useful if downstream equipment recognizes it. In the case of DVD, a license agreement needed to play encrypted contents may also legally bind the manufacturer to detect watermarks. DVD Audio uses a watermark system developed by Verance.
The license that enables the drive to play CPPM or CPRM discs obligates the manufacturer to detect the watermark.
DVD-Audio recorders recognize CCI copy-generation watermarks.
FIG. 24 The abandoned HD DVD format provided greater storage capacity
and higher output bit rate than DVD. HD DVD discs use two 0.6-mm substrates.
A single sided disc is shown, but the specification also supports double-sided
discs.
HD DVD
The HD DVD format was envisioned as the successor to the DVD-Video format. This high-density disc format was designed primarily to deliver high-definition playback of motion pictures. Players and discs were introduced in March and April 2006, but the HD DVD format ultimately did not find commercial success against the competing Blu-ray system. In February 2008, its principal backer, Toshiba, announced that it would no longer develop or manufacture HD DVD players or drives. Soon thereafter, the format was abandoned in the marketplace.
The HD DVD format (High Density) uses a 405-nm blue light laser and NA of 0.65 to achieve high storage capacity.
An HD DVD-ROM disc holds 15 Gbytes on a single-layer disc and 30 Gbytes on a dual-layer disc. The structure of the HD disc is shown in FIG. 24. The VC-9 video codec used in Microsoft Windows Media 9 (WM9), MPEG-4 H.264 Advanced Video Codec (AVC), and MPEG-2 are mandatory video codecs for all licensed HD DVD players.
Dolby Digital Plus and DTS are mandatory audio-coding formats. Lossless MLP 2-channel coding is mandatory and lossless DTS coding is optional. AES encryption is used to copy-protect contents. In addition, rewritable HD DVD discs have been developed. A single-sided, single-layer HD DVD-RW disc holds 20 Gbytes and a double-sided, single-layer disc holds 40 Gbytes. A single-sided, single layer HD DVD-R disc holds 15 Gbytes. HD DVD was supported by the DVD Forum.
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