DVD-Video Developer's Summary
Programmers and others developing DVD-Video products should know the specific definitions of terms, file structures, and the interrelationships of file types. This section provides such overview information. As noted, the Part 3 DVD-Video format adheres to Parts 1 and 2 of the DVD specification. It employs the UDF file format; Part 3 specifically defines how the user can access disc contents (Navigation) and how the video data itself is structured (Video Objects). Discs can contain multiple titles; for example, there might be a movie and a trailer, or perhaps several short films. The Title is a disc's highest level of navigation, and users select which title they wish to view.
Internally, the title manager contains one or more Video Title Sets (VTSs) and Program Chains (PGCs) that also contain audio and video elements. Within each title, a main menu shows particular contents, possibly leading to submenus. Typically, four directional buttons are used for onscreen selection, and an enter button activates selections within a menu. Other dedicated buttons access specific features such as audio tracks and subtitles. This and other navigation structure is defined in Part 3.
Part 3 defines a video disc for moving pictures. The Presentation data structure complies with the MPEG-1 and MPEG-2 specifications. A Pack is a pack header followed by one or more packets. A Pack is a layer in the system coding that is described in ISO/IEC 13818-1 (the MPEG-2 stream layer specification). MPEG 13818-1 defines disc program stream and broadcast transmission stream; 13818-2 defines video compression; 13818-3 defines audio compression for surround sound. (MPEG-1 is defined in ISO 11172-1, -2, and -3.) A Packet is the elementary data stream following the header; there are five kinds of Packets. A Stream-ID defines the type of packet and is defined in ISO/IEC 13818-1. An ISO/IEC 13818-1 stream contains five packetized elementary streams of video, audio, sub picture, presentation control information (PCI ), and data search information (DSI ). A Cell is a group of MPEG frames of indeterminate length starting and ending with an I -frame. An I -frame is an intra-coded picture without temporal prediction, as opposed to P (forward-predicted) frames and B (bidirectional) frames. Cells are used by PGCs, which are part of the Navigation system. (There are also audio cells.)
A Program Chain (PGC) contains navigation pointers to cells and cell groups. These PGCs can be selected by the viewer. For example, one PGC pointing to cells 1 to 20 and 35 to 50 would show the G-rated version of a movie, and another PGC pointing to cells 1 to 50 would show the complete R-rated version.
The Volume Space of a DVD-Video disc consists of the Volume and File structure, a single DVD-Video zone, and DVD-Other zone (see FIG. 11A). A DVD-Video zone consists of one Video Manager (VMG) and one or more Video Title Sets (VTSs). The VMG is the table of contents for all Video Title Sets; each VTS is a collection of titles.
The VMG contains a main menu for disc title, text data, and so on. A Video Title Set is a collection of titles. A VTS contains a menu for title section, language for audio/sub picture, playback control information (PGCI ), and audio video VOBS data. A Video Object Set (VOBS) is a collection of Video Objects (VOBs) that hold presentation data such as video, audio, or sub-picture data. For example, a VOB might contain all of an MPEG-2 video program. A Title consists of one or more PGCs, each containing Program Chain Information and VOBs. Titles with multiple PGCs permit branching, multiple story lines, etc. The DVD-Video data structure is shown in FIG. 15.
A DVD-Video zone also contains Navigation data (playback control) and Presentation data (the video program to be played back). The Navigation Manager handles navigation data (VMGI , VTSI , PCI , and DSI ) to control the user interface, control playback, interpret user actions, and determine how the Presentation Engine should play back Presentation data. A Button is an onscreen user control; Buttons are defined in PCI . A Menu is an onscreen display that includes Buttons.
FIG. 15 The DVD-Video data structure can be viewed as a disc image with
the DVD-Video zone holding the Video Manager and Video Title Sets. DVD-Audio
follows the same structure.
The Presentation Engine follows instructions issued by the Navigation Manager to play Presentation data from the disc and control the displayed output. Presentation data is divided into cells. Presentation data consists of VOBs. For example, a section may be a VOB. Different VOBs may be used for different scenes, cuts, and so on (for director's cut, angles, parental lockout, and the like). A VOBS consists of one or more Video Object blocks.
Navigation data consists of attributes and playback control for the Presentation data. Navigation data allows the user to access disc contents. Content providers can use this data to code branching and interactivity. There are four types: Video Manager Information (VMGI ), Video Title Set Information (VTSI ), Presentation Control Information (PCI ), and Data Search Information (DSI ). VMGI is described in the Video Manager (VMG). It describes information in the VIDEO_TS directory. Data includes a video copy flag, an audio copy flag, number of volumes, disc side identifier, NTSC/PAL, aspect ratio, picture resolution, number of audio streams, audio-coding method, quantization, sampling rate, number of channels, sub picture coding, menu language, and parental management.
Video Title Set Information (VTSI ) is described in the Video Title Set (VTS). It describes information for one or more Video titles and the Video Title Set Menu. Its data is similar to VMGI . PGCI pointers are the Navigation data used to control presentation of the PGC and order of cell playback. PGCI pointers are usually played sequentially, but can be played in random or shuffled sequence. PGC is composed of PGCI and VOBs. For example, PGC may be used to create interactive programs. PGC has data such as presentation time in hours, minutes, seconds, frames, and cell information. PCI is dispersed in the VOBS along with Presentation data. PCI is the Navigation data used to control the presentation of a VOB Unit (VOBU). PCI is used by the playback engine to control what is seen and heard.
PCI has data such as angle information, highlight information, relation between sub-picture and highlight, and buttons.
Data Search Information (DSI ) is dispersed in the VOBS along with Presentation data. DSI is the Navigation information used to search and seamlessly play back the VOBU. DSI is also used for navigation and search control (such as branching). DSI has data such as interleaving, start address, and synchronization. Navigation Commands are used by content providers to allow changes in player operation including branching and interactivity (as opposed to linear playback). Navigation commands appear in PCIs and PGCIs. DVD-Video uses Navigation commands to provide a high degree of interactivity. Linking, looping, jumping, searching, and decision making are built into the specification as navigation commands. Software developers use this standardized command set. There are twenty-four 16-bit System Parameters (SPRMs) registers (such as angle number, video capability, audio capability, parental level, and language code) for player settings and sixteen 16-bit General Parameters (GPRMs) registers (such as go to, jump, link, and compare) to memorize the user's operational history and modify the player's operation.
A hardware splitter/navigator controls DVD playback. It uses PCI information that describes the stream contents, and then splits the data to the appropriate decoders. The navigation engine uses DSI information and user input to control playback. Omitting PCI and DSI , the three remaining stream types have a maximum bit rate of 9.8 Mbps (variable). In practice, the average rate might be 4.7 Mbps.
A VOB contains Presentation data (video data, audio data, sub-picture data, and VBI data) and part of the Navigation data (PCI and DSI ). Video Objects are defined as pack types and have restrictions on data transfer rate.
The video stream (maximum of 1) has a maximum transfer rate of 9.80 Mbps; the PCM audio stream (maximum of 8) has a maximum transfer rate of 6.144 Mbps; the sub picture stream (maximum of 32) has a maximum transfer rate of 3.36 Mbps.
A Video Object Set is a collection of Video Objects, as shown in FIG. 16. Each VOB can be divided into cells (or scenes). Each cell contains Video Object Units that are groups of audio or video blocks; a cell is the smallest addressable data chunk, but may last for a moment or for a movie's entire duration. Each VOBU contains VOB pack types such as V_PCK (video packs), A_PCK (audio packs), and NV_PCK (navigation packs). VOBUs may also contain analog copy-protection data for Macrovision. A pack comprises packets and both comply with ISO/IEC 13818-1 (the MPEG-2 bitstream format, not the MPEG-2 audio or video coding formats). A pack is 2048 bytes total with up to 2034 bytes of user information. FIG. 17 shows the structure of a pack. Navigation Packs (NV_PCK) contain PCI (979 bytes) and DSI (1017 bytes) data. Sub-picture packs (SP_PCK) contain sub-picture data (2024 bytes). Video Blanking Information (data placed in the video blanking period) packs (BVI_PCK) contain VBI (640 bytes). Video packs (V_PCK) contain video data (2025 bytes). Audio packs (A_PCK) contain audio data such as PCM (2013 bytes), AC-3 (2016 bytes), and MPEG (2020 bytes). An audio pack contains data such as audio emphasis, audio mute, audio frame number, quantization word length, audio sampling frequency, number of audio channels, dynamic range control, copyright, and so on.
To summarize, audio and video data as well as presentation and control information are held in packets.
Usually, one MPEG Group of Pictures (GOP) occupies one VOBU. VOBUs are collected into cells. Sequences of cells comprise a program that is stored in a VOB. Sequences of programs comprise a Presentation Control Block (PCB).
This, along with command information, creates a Program Chain. Its audio and video content is stored in a VOBS.
Titles are grouped to form a VTS.
FIG. 16 A Video Object Set (VOBS) is a collection of Video Objects, which
in turn contain cells, and Video Object Units, which contain pack data.
FIG. 17 The structure of packs and packets used in DVD-Video adheres to
the MPEG-2 standard. Presentation data is contained in packets.
In the DVD-Video player, packs in the program stream are received from the disc and transferred to the appropriate decoder. A buffer is used to ensure a continuous supply of data to the decoders. DSI data is treated separately. Video presentation data complies with ISO/IEC 13818-2 (MPEG-2 video standard) or ISO/IEC 11172-2 (MPEG-1 video standard). MPEG places constraints on the picture coding. Video data is split into VOBUs. Video data in a VOBU consists of one or more GOP. Audio presentation data comprises PCM or compression coded data such as AC-3, DTS, or MPEG.
The audio stream is divided into packs and recorded on the disc. Sub-picture presentation data comprises the sub picture header unit, pixel data, and display control sequence table. Video Blanking Information Unit presentation data is placed in the blanking period.
DVD-Audio
The DVD-Audio portion of the DVD specification describes a high-quality audio storage format that provides a wide variety of channels, sampling frequencies, word lengths, and other features. Although primarily an audio specification, it also provides for incorporation of video and other elements. In many ways, DVD-Audio is based on the DVD-Video specification. Development of DVD-Audio began in December 1995, with the formation of the DVD Forum's Working Group 4 (WG-4). Its first meeting was held in January 1996, and Version 0.9 of the specification was released in June 1998. The DVD-Audio Version 1.0 specification was finalized in February 1999, and was the last of the original DVD formats to be ratified by the DVD Forum. DVD-Audio products were introduced in early 2000. WG-4 received input from the International Steering Committee (ISC) representing the interests of the major record labels through trade associations (RIAA, IFPI , and RIAJ). The ISC established 15 criteria for DVD-Audio such as high-quality sound, multichannel audio, scalable parameters, CD compatibility, long playing time, optional video content, simple or menu-based disc navigation, and copy protection.
Although the DVD-Video format can provide high-quality audio (such as six channels of 48-kHz/20-bit audio) its maximum audio bit rate of 6.144 Mbps cannot support the highest quality levels. DVD-Audio's maximum bit rate of 9.6 Mbps increases its abilities. For example, with PCM coding, six channels of 96-kHz/16-bit audio is allowed.
However, six channels of 96 kHz/24-bit PCM audio exceeds the maximum bit rate. In any case, high bit-rate PCM streams reduce playing time. Thus lossless and lossy compression algorithms can be optionally employed to reduce bit rate demands, and increase playing time.
The primary intent of the developers was to create an audio format that would retain compatibility with other DVD disc formats, some backward compatibility with the CD format, and introduce improved sound quality and multichannel playback. In addition, DVD-Audio would protect its content with stringent anti-piracy measures. To augment the already large capacity of DVD, DVD-Audio also provides for lossless data compression of audio. This option allows storage of over 74 minutes of high-quality multichannel music on a single data layer. DVD-Audio discs must contain an uncompressed or MLP-compressed PCM version of the DVD-Audio portion of the program. For further flexibility and added compatibility with existing DVD Video players, DVD-Audio discs may also include video programs with Dolby Digital, DTS and/or PCM tracks. In most cases, in addition to high-resolution PCM tracks, DVD-Audio discs also contain Dolby Digital tracks, so that discs are playable in both DVD-Audio and DVD-Video players. Dolby Digital tracks are mandatory on discs that contain associated video tracks.
Two types of DVD-Audio discs are defined. An Audio Only disc (see FIG. 11B) contains only music information.
An Audio-Only disc can optionally include still pictures (one per track), text information, and a visual menu. In addition, an Audio with Video (AV) disc is defined (see FIG. 11C); it can contain motion video information formatted as a subset of the DVD-Video format.
DVD-Audio Coding and Channel Options
The DVD-Audio format supports a variety of coding methods and recording parameters, as shown in Table 4.
PCM tracks are mandatory on all discs. Optional disc coding methods include MLP, Dolby Digital, MPEG-1, or MPEG-2 without extension bitstream, MPEG-2 with extension bitstream, DTS, DSD, and SDDS. DVD-Audio is said to be extensible; it is open-ended and can be adapted to future coding technologies. All DVD-Audio players must support MLP decoding. DVD-Audio is a "scalable" format; that is, its specification provides considerable flexibility for content providers. When PCM coding is used, the number of channels (1 to 6), the word length (16, 20, 24 bit), and the sampling frequency (44.1, 48, 88.2, 96, 176.4, or 192 kHz) can be interchanged. At the highest sampling frequencies of 176.4 kHz and 192 kHz, only two-channel playback is possible. To limit the output bit rate to the 9.6-Mbps maximum, other restrictions may apply to lower sampling frequencies. Audio attributes such as sampling frequency and word length can be set differently for each track.
The coding options, range of sampling frequencies and word lengths, and number of titles (stereo and/or multichannel) create a range of playback times. In addition, the number of disc layers determines playing times. For example, depending on its recording parameters, a stereo PCM program on a data layer might play for 422 or 65 minutes. Similarly, different configurations of multichannel recordings will yield a range of playing times, as shown in Table 5. MLP lossless compression can effectively almost double the disc capacity, thus increasing playing times. The compression achieved by MLP depends on the music being coded. Very approximately, it gives about a 1.85:1 compression ratio; thus, it can almost halve bit rate, and double playing time with no loss of audio quality.
Similarly, lossy compression increases playing time. Dolby Similarly, lossy compression increases playing time. Dolby Digital, DTS, MPEG, MLP, and other audio codecs are discussed in more detail in Section 11.
Table 4 The DVD-Audio specification supports a variety of coding methods,
each with many possible recording parameters. Some examples are shown here;
this table is not inclusive of all possibilities.
Table 5 Examples of coding methods and recording parameters and resulting
playing times per disc layer (DVD-5).
The use of high sampling frequencies such as 96 kHz and 192 kHz may seem unnecessary. In rare cases, a person may be able to hear frequencies of 24 kHz or 26 kHz, far below the cutoff frequencies of 48 kHz and 96 kHz.
In most cases, high-frequency hearing response is below 20 kHz. Thus, for steady-state tones, the higher frequency response may not be useful. However, it can be argued that high sampling frequencies improve the binaural time response, leading to improved imaging. For example, if short pulses are applied to each ear, a 15-ms difference between the pulses can be heard, and that time difference is shorter than the time between two samples at 48 kHz.
Some people can hear a 5-ms difference, and that corresponds to the time difference between two samples at 192 kHz. In theory, this high sampling frequency may improve spatial imaging. Thus, it may take two ears to distinguish between a recording at 48 kHz, and one at 192 kHz. Its designers hoped that the DVD-Audio specification would offer improvements in fidelity and in any case its specifications would not be a limiting factor.
Various channel assignments can be made by placing the channels into two Channel Groups (CGs); examples of channel assignments are shown in Table 6. This prioritizes mixes that use the front L and R channels; front L, R, and C channels; and the corner L, R, Ls, and Rs channels. The sampling frequency and word length of CG1 is always greater than or equal to those of CG2, as shown in Table 7. Generally, CG1 assignments are for the front channels, and CG2 assignments are for the rear channels.
There are numerous ways to assign channels, ranging from monaural to six channels, and different word lengths and sampling frequencies can be employed on the front and rear channels. For example, front channels could be coded at 24/96 with the rear channels coded at 16/48. Coding the rear channels at a lower bit rate, for example, would allow longer playing times, or would allow disc capacity to be budgeted to other content such as videos or stereo mixes.
Table 6 DVD-Audio channel assignments are made with two Channel Groups (CG1
and CG2). Assignments enable front mixes, front mixes with center channel,
and four channel corner mixes. There are other possible assignments beyond
the 21 examples shown here.
Sampling frequencies in channel groups must be in the same family, that is, related by a simple integer such as 48/96/192 kHz or 44.1/88.2/176.4 kHz. Table 8 shows examples of different channel configurations for 5.0- and 5.1-channel playback using PCM coding. Unlike some 5.1 channel systems (Dolby Digital, DTS, MPEG), the PCM coding used in DVD-Audio does not bandlimit the LFE channel, it is a full-bandwidth channel. The choice of sampling frequency family is probably best determined by the sampling frequency of the original recording; noninteger sample rate conversion might introduce audible artifacts.
The frame rate is defined to be 1/600 second at sampling frequencies of 48, 96, and 192 kHz, and 1/551.25 second at 44.1, 88.2, and 176.4 kHz.
Table 7. The Channel Groups are scalable. The sampling frequency and word
lengths of CG1 must be greater than or equal to those of CG2.
Table 8 Examples of multichannel PCM channel configurations with multiple
sampling rates, showing bit rate and playing time (on single-layer/dual-layer
discs). A. 5.1 channels coded at 48 kHz/96 kHz. B. 5.0-channels coded at 48
kHz/96 kHz.
PCM coding also provides for an emphasis characteristic (zero at 50 ms and pole at 15 ms, for sampling frequencies of 48 kHz and 44.1 kHz); this boosts high frequencies during encoding and correspondingly cuts high frequencies during decoding to reduce the noise floor.
This can be applied when all channels use the same sampling frequency. Use of pre-emphasis is optional on discs, but provision for de-emphasis is mandatory in players. PCM coding can also employ a dynamic range control (the same provision as in the DVD-Video specification). This is a disc option and player requirement.
A DVD-Audio disc can contain one or several selections, as provided by a content provider. For example, a disc might contain one selection coded as PCM; every player could play back this selection. Another disc might contain two selections, one coded as PCM multichannel and the other coded as PCM stereo; the provider can choose the order of the selections; only players with multichannel capability could play the multichannel selection. Another disc might contain two selections, one coded as PCM stereo and the other coded in an optional format such as Dolby Digital; the optional selection could be played by players equipped with that circuitry. It is advantageous to place Dolby Digital tracks on a DVD Audio disc so they can be played in a DVD-Video player. A single-inventory disc may include: DVD-Audio stream of up to six channels of MLP at 96/24, stereo PCM stream, Dolby Digital 5.1-channel stream on the DVD-Video portion, and possibly even a Red Book layer at 44.1/16.
DVD-Audio discs can employ the SMART (System Managed Audio Resource Technique) feature with PCM tracks. SMART provides automatic downmixing so that a multichannel audio program can be mixed down to two channels by the player during playback and thus replayed over a stereo playback system. The content provider can program how the downmixing will occur, by selecting one of 16 coefficient tables, stored along with the audio data on the disc. Each coefficient table defines level, pan position, and phase. The level mixing ratio can vary from 0 to -60 dB. Coefficient tables can be varied on a track-by-track basis in each Audio Title Set. The SMART feature eliminates the need to include a separate stereo mix on a multichannel disc, thus wasting disc space. However, SMART may not allow the creative flexibility demanded by some content providers. When a separate stereo mix is coded along with a multichannel mix, the separate mix is automatically selected instead of a folded-down mix. Use of SMART downmixing is optional on discs, but its support is mandatory in players.
MLP supports the downmix feature. The player first decodes the multichannel signal and then accesses the coefficients to provide a two-channel playback. Optionally, the downmix can be created by the MLP encoder rather than the player so both two-channel and multichannel mixes can be conveyed separately by MLP sub-streams. The MLP decoder in the player reads the two-channel substream and outputs two channels. This reduces the computation required in stereo-only players. However, the two-channel mix increases the bit rate by about one bit per sample. For multichannel playback, the player extracts both sub-streams and the MLP decoder decodes all channels prior to possible downmixing.
Other "value-added" content on DVD-Audio discs may include artist names, song titles, liner notes, artist commentary, biographies, discographies, music videos, and Internet URLs. Non-real-time information (such as content) is recorded in Information areas while real-time information (such as lyrics) is recorded in Data areas. Two character sets are supported: ISO 8859-1 for European languages and Music Shift JIS for Japanese. Multiple languages may be supported. Still images may be tagged to individual tracks; they may be displayed like a slide show (manual or automatic) while the music plays. Likewise, text and sound effects may be played in real time. This extra information is a disc option (track names are mandatory if there is any text information), but decoding must be supported by Universal players (described below). In some cases, the player uses the text information to construct a text menu.
Full motion video can be added to a DVD-Audio AV disc as an independent video portion; it is defined as a subset of the DVD-Video specification. Several restrictions apply: there is a maximum of two audio streams, at least one of which must be PCM and the PCM stream is limited to six channels with restricted channel assignments. In addition, there is no multi-story, multi-angle, parental control, or region control features. There is no mandatory PCM audio in the DVD-Video portion of disc (there is already a PCM version in the DVD-Audio part). Dolby Digital is mandatory in the DVD-Video portion (PCM is optional). DVD-Audio also defines a DVD-ROM zone that can contain compressed audio files. These files can be moved, for example, to portable music players. MPEG-4 High-Efficiency AAC (HE AAC), also known as aacPlus, files can be placed in this compressed audio zone.
DVD-Audio Disc Contents
DVD-Audio disc contents are arranged hierarchically as shown in FIG. 18. One album (or volume) describes the entire contents of one disc side. An album can contain up to nine groups. A group can contain up to 99 tracks. A track may contain up to 99 indices (in an Audio-Only disc).
FIG. 19 shows an example of the contents of a DVD Audio Audio-Only disc. This disc contains two groups; in this case, Group 1 holds five main tracks and Group 2 holds two alternate remixed tracks. In addition, each group has two selections (labeled #1 and #2); for example, tracks 1 and 2 in Group 1 have two selections. In track 1, selection #1 is a multichannel mix and selection #2 is a stereo mix (downmixing is not used). Tracks 3, 4, and 5 may use downmixing. In this example, Group 2 selection #2 tracks use optional coding. Each group has one or more Audio Title Sets, and the tracks are objects within the Audio Title Sets.
FIG. 18 Contents of DVD-Audio discs are arranged hierarchically. Any track
in an album is accessible using a group number and track number.
FIG. 19 An example of the contents of a DVD-Audio Audio-Only disc, showing
two groups with a total of seven tracks.
FIG. 20 An example of the contents of a DVD-Audio AV disc, showing one
group with seven tracks.
Table 9 Compatibility between DVD-Video and DVD Audio discs, and four types
of players: Audio-Only player, Video Capable Audio player, Universal player,
and Video player.
An example of the contents of a DVD-Audio AV disc is shown in FIG. 20. There is one group in this album. It has five audio-only tracks and two AV tracks. Tracks 1 and 2 have two selections; for example, in track 1, selection #1 is a stereo mix and selection #2 is a multichannel mix. Tracks 6 and 7 have video components (not playable on an Audio Only player). The group has three Titles (two Audio Title Sets and one Video Title Set). The tracks are objects within the ATS and VTS.
DVD-Audio players (without video capability) can play back the audio contents and audio components of video contents of DVD-Audio AV discs. They can play selected audio components on DVD-Video VAN discs. Disc and player compatibility is illustrated in Table 9. DVD-Video players cannot play the high-resolution PCM tracks in the DVD-Audio zone. However, the video zone in DVD-Audio discs adheres to the DVD-Video format. Thus, for partial compatibility with DVD-Video players, many DVD-Audio discs contain a stereo PCM or Dolby Digital version of the album in their video zone. DVD-Audio players can also play hybrid DVD-Audio discs that contain both a DVD-Audio data layer and a Red Book CD layer. The DVD-Audio format also supports a SACD-like disc (Super Audio CD) as an optional format, thus some players can play both DVD and SACD discs. Universal DVD players can play the spectrum of DVD-Audio and DVD-Video discs. Mandatory player functions include user transport controls, selection of groups and tracks, and track searches. Optional features include group search, index search, visual menu, random play, and highlight selection. The visual menu is a subset of the DVD-Video menu specification; it is used to select groups and tracks, view multiple languages, and view still information such as liner notes and images. The visual menu is optional for Audio players but mandatory for Universal players.
The Simple Audio Play Pointer (SAPP) facilitates user navigation of the disc contents. SAPP information is contained in a table located in the disc lead-in area (it is similar to the TOC in the Red Book specification). SAPP is a subset of the more sophisticated and general Audio Navigation table; SAPP provides basic information for monaural and stereo PCM playback only, usually in simple players.
As with other DVD discs, DVD-Audio uses a robust RS PC error correction system that includes a wide interleave.
Local disc damage can cause unreadable data; the player's response depends on how the navigator is implemented. If the navigator attempts to reread the damaged sector, its success partly depends on the data rate. If the rate is low, the player may have time to reread without an interruption in the output data; if the rate is high and especially near the maximum rate of 9.6 Mbps, there may not be time for a reread, and the data output may be interrupted. cont.>>