Recording Process Methods of writing a DVD-R CD-R Versus DVD-R
DVD-RAM DVD Phase-Change Rewritable, called DVD+RW DVD-R/W
Applications of Recordable DVD
DVD Mastering The Players The Features of DVD-Video Video Details
MPEG2 Video Compression Interactivity Aspect Support: MPAA Rating Control and Multiple Film Versions
Linear PCM Dolby Digital (AC-3) MPEG Audio
Comparison to The Other Media
DVD production Benefits of DVD
What Is DVD?
DVD is the next generation of digital optical disc technology. A DVD is the same size as a Compact Disc but holds up to 25 times more and is faster than 12X CD-ROM drives. The way information is stored on the disc has been improved, allowing 8-channel surround sound, 8 language tracks, 32 subtitle and karaoke tracks, automatic branching of video (so G, PG-13, and R versions of a movie can be viewed from a single disc), multiple camera angles, and other exciting features.
During introduction of CD, consumer electronic companies have been developing new techniques to increase the density of the standard CD. Digital coding and compression algorithms have become vastly more sophisticated. Moreover, integrated circuits and drive mechanisms have made impressive advances.
All of these advances came into play when companies began to work on the next generation of optical media. The goal: vastly increased capacity, with the ability to feature an entire movie in high-quality digital video on a single side of a disc.
This was the start of DVD.
We can say that DVD is two separate things:
A computer data storage medium.
An audio/video storage medium.
The primary "flavours" of DVD:
DVD-ROM -- the disc media that holds computer data, to be read by a computer's DVD-ROM drive.
DVD-WO (also known as DVD-R) -- a variation of DVD-ROM that supports one-time recording.
DVD-RAM, DVD-RW, DVD-R/E -- rewritable DVD.
DVD-Video (also known as DVD-Movie) -- which is a disc that holds video and or audio programs such as feature films that can be played back by either a DVD-Video player or a DVD-ROM enabled computer, on a large screen display such as a TV.
Features of DVD
As with Compact Disc, DVD will be durable, and tolerant of dust, dirt and fingerprints. Not susceptible to magnetic fields or RF interference. Resistant to heat. (Limited exposure to the sun does not melt the media). Data can be stored on both side in a duble Layer form
Configurations of DVD data layers
The basic configuration of Single Side, Single Layer is 4.7 GB of data capacity
The Single Side, Dual Layer configuration provides a total of 8.5 GB on one side using an additional 3.8 GB on the second layer.
The Double Side, Single Layer configuration provides total of 9.4 GB (4.7 on each side).
The Double Side, Dual Layer configuration provides the maximum capacity of 17 GB.
The focusing mechanism is the technology that allows data to be recorded on two layers. The lens system in some drives utilizes a holographic lens which allows two focal lengths allowing silver CDs and DVDs to be read without a separate laser or lens system. A limitation of first generation PC-DVD drives was their inability to read CD-Recordable media (CD-R). Second-generation PC-DVD drive uses a dual laser, single lens design that can read CD-R media.
Connectivity is similar to that of CD-ROM drives: EIDE (ATAPI), SCSI-2, etc. All DVD-ROM drives have audio connections for playing audio CDs.
DVD-ROMs use a MicroUDF/ISO 9660 bridge file system. The UDF file system will eventually replace the ISO 9660 system of CD-ROMs, but the bridge format provides backwards compatibility until operating systems support UDF.
UDF Features :
Enables operating system independent interchange on optical media
Designed to support the massive capacities of optical jukeboxes
Only ISO standard file system for WORM media
Industry selected file system for 2nd generation CD-ROM or for DVD.
Enables full interchange between computer-based and entertainment-based media
Compared to CD, DVD uses smaller pits and a more closely spaced track. The result is a significant increase in data density. The higher Numerical Aperture (NA) lens of DVD helps the laser focus on the smaller pits. The increase in capacity from CD-ROM is due to:
smaller pit length (~2.08x)
tighter tracks (~2.16x)
slightly larger data area (~1.02x)
more efficient channel bit modulation (~1.06x)
more efficient error correction (~1.32x)
less sector overhead (~1.06x).
DVD's digital modulation and error correction schemes have been specifically designed to support the increase in capacity. The 8 to 16 (EFM PLUS) modulation scheme is highly efficient and ensures backward compatibility. And the RS-PC (Reed Solomon Product Code) error correction system is approximately 10 times more robust than the current CD system. Most DVD-ROM drives have a seek time of 150-200 ms, access time of 200-250 ms, and data transfer rate of 1.3 MB/s (11.08*10^6/8/2^20) with burst transfer rates of up to 12 MB/s or higher. The data transfer rate from DVD-ROM discs is roughly equivalent to a 9x CD-ROM drive. DVD spin rate is about 3 times faster than CD, and a few DVD-ROM drives read CD-ROM data at 3x speed, most of first generation DVD-ROM drives read CD-ROMs at 12x, second generation drives read up to 24x speeds.
While it is possible to obtain 30x speeds from CD-ROM drives, often compromise in hardware configuration or software will limit that speed and sharply diminish the actual speed obtained.
Mainly there are two versions of recordable DVD : Record Once (DVD-R) and Rewritable (DVD-RAM, DVD-RW, DVD-R/W).
DVD-R is a write-once format, like CD-R, uses a constant linear velocity rotation technique to maximize the storage density on the disc surface. Recording begins at the inner radius and ends at the outer. Rotation of the disc therefore varies from 1,648 RPM to 648, depending on a record/playback head's position over the surface.
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 disc. The substrate is injection molded, and has a microscopic, "pre-groove" spiral track formed onto its surface. This 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 the bonding process.
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 layer 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 a recording. Playback occurs by focusing a lower power laser of the same approximate wavelength (635 or 650 nm) onto the surface of the disc. The "land" areas between marks are reflective, meaning that most of the light is returned to the player's optical head. Conversely, recorded marks are not very reflective, meaning that very little of the light is returned. This "on-off" pattern is thereby interpreted as the modulated signal, which is then decoded into the original user data by the playback device.
Blank DVD-R discs are recorded in a special drive that is controlled by a host computer. The recording process is orchestrated by application software that allows a user to specify which files will be transferred to the disc as well as controlling the actual recording itself.
All DVD discs, recordable or not, must have three basic areas recorded on them: lead-in, user data and lead-out. The lead-in and lead-out areas are boundaries that indicate to a playback device where the inner and outer limits of a recording are respectively. They contain no user accessible information, but are critical to the proper functioning of a disc.
There are two methods of writing a DVD-R disc: disc-at-once and incremental writing.
Disc-at-once, as its name implies, is the process of writing an entire disc's worth of data at one time. Data must be consistently provided by a host computer at a full 11.08 megabits per second during any recording to avoid buffer underrun errors. The occurrences of underruns can be minimized by the use of a large writing buffer memory in a DVD-R drive. DVD-R disc-at-once writing is performed such that the lead-in, data area and lead-out areas are all written sequentially. This differs from CD-R disc-at-once writing, where the data area is written first, followed by the lead-in and lead out areas.
Incremental writing allows a user to add files directly to a DVD-R disc one recording at a time instead of requiring that all files be accumulated on a hard disk prior to writing as with the disc-at-once method. The minimum recording size must be at least 32 kilobytes, (even if the file to be recorded is smaller) as this is the minimum error correction code (ECC) block size for DVD. Obviously, a disc that is being written to incrementally cannot be considered a complete volume until the final information has been stored or the disc capacity has been reached. The lead-in and lead-out boundary areas therefore cannot be written until either of these two events occur. Such an "unfinalized" disc (one without lead-in, lead-out and complete file system data) can only be read by a DVD-R drive until this process can be completed. After finalization, a disc can then be read by a destination playback device, but can no longer have data added to it.
CD-R Versus DVD-R
The primary advantages of DVD-R drives, are higher capacity and compatibility with all DVD players and drives. To help achieve increase in storage density over CD-R, two key components of the writing hardware needed to be altered: the wavelength of the recording laser and the numerical aperture (n.a.) of the lens that focuses it.
The table below highlights the differences between some basic parameters of both media formats:
635 - 645 nm
775 - 795 nm
635 - 650 nm
770 - 830 nm
4 - 11 mw
4 - 8 mw
R14H > 0.5
RTOP > 0.65
The rewritable DVD's specification is based on input from a wide range of sources, including end users, PC manufacturers, CD- and DVD-ROM drive manufacturers, media manufacturers and software developers. The DVD specification is designed to offer data-storage and distribution markets a smooth migration path from CD to DVD.
As rewritable DVD technology is new, there isn't an unic format yet. Different companies applay diffferent formats. At the moment there are three type of rewritable DVD. These are: DVD-RAM, DVD-RW and DVD-R/W.
Because of this, compatibility is the problem of recordable DVD. To override this problem the DVD+RW group offers a solution for future data-storage requirements, By eliminating the need for a caddy, ensuring CD-R compatibility and offering a slightly higher capacity.
DVD-RAM (originally envisioned as a cartridge-encased disc able to store up to 2.6GB of data on a side) uses phase-change (PD) technology and is not compatible with current drives (because of defect management, reflectivity differences, and minor format differences). A wobbled groove is used to provide clocking data, with marks written in both the groove and the land between grooves. The grooves and pre-embossed sector headers are molded into the disc during manufacturing. Single-sided DVD-RAM discs come with or without cartridges. There are two types of cartridges: type 1 is sealed, type 2 allows the disc to be removed. Double-sided DVD-RAM discs are in a sealed cartridges only. These cartridges privent DVD-RAM discs from being read by DVD-ROM drives or players. Cartridge dimensions are 124.6mm x 135.5mm x 8.0mm. Future DVD-RAM discs may use a contrast enhancement layer and a thermal buffer layer to achieve higher density. Some companies has announced reaching 5.2 billion bytes by reducing mark size from 0.41/0.43 microns to 0.28/0.30 microns and track pitch from 0.74 microns to 0.59 microns.
DVD Phase-Change Rewritable, called DVD+RW without the blessing of the DVD Forum, is a competing erasable format. DVD+RW drives will read DVD-ROMs and CDs, but are not compatible with DVD-RAM. Minor changes to DVD-ROM drives will allow them to read DVD+RW discs. DVD+RW, which holds 2.8 gigabytes (3G) (NEC's MMVF format promises 5.2GB of data on each side) uses phase-change technology with wobbled groove and either CLV format for sequential video access (read at CAV speeds by drive) or CAV format for random access. The disc have a track pitch of 0.80 mm a user data rate of 7 to 17 Mbits/sec. and allow more than 100.000 direct overwrite (DOW) cycles.
DVD-R/W is yet another announced phase-change erasable format. Based on DVD-R, DVD-R/W uses the same track pitch, mark length, and rotation control, and should be playable in first-generation DVD drives and players. DVD-R/W uses groove recording with address info on land areas for synchronization at write time (land data is unnecessary during reading). Capacity is 3.95 billion bytes, later can be expanded to 4.7.
Applications of Recordable DVD
With the growing trend of multimedia documents that require large amounts of disc space, recordable DVD offers the ability to create, share, store and access these content-rich documents easily using a single disc. As documents get continually richer with the incorporation of audio, video and complex graphics, there is a growing need to deliver larger storage solutions. However, those solutions must be as easy to use as floppies or CDs. DVD-R's relatively low cost per megabyte, coupled with its physical storage efficiency and the portability of its recording equipment makes the medium applicable to a large variety of uses in virtually all industries. There are three fundamental applications anticipated for DVD-R:
Testing and Development
Storage and Archival
DVD Video is the new way in home entertainment. A single DVD Video disc can hold an entire movie on one side while bringing together the high-quality, digital surround sound of compact discs with crisp, high-resolution video. As a system it consists of a mastering system, a physical distribution medium (the disc itself) and a player.
After a movie has been transferred from photographic film to video tape, it must be specially formatted before it can be distributed on a DVD. The mastering process consists of several steps, as listed below and illustrated in Figure:
Scanning the video tape to identify scene changes, insert pan-and-scan codes, enter closed-caption information and mark objectionable sequences that would be subject to parental lockout
Compressing the video in MPEG-2 format using a process called variable bit rate encoding
Compressing the audio tracks into Dolby AC3 Surround Sound format.
Simulating the playback of the disc in the mastering system, a process called emulation
Writing out a data tape with the "image" of the DVD
Creation of a glass master, which replicators use to "press discs"
All but the last of these processes are performed using a mastering system, which is based on a high-performance workstation computer. However, this computer is merely the host or controller for two very powerful digital signal processing systems: one to encode the video and the other the audio.
The players consist of the following major components:
Disc Reader Mechanism: consists of the motor which spins the disc and the laser which reads the information.
The DVD-DSP (digital signal processor): an integrated circuit that translates the laser pulses back into electrical form that other parts of the decoder can use.
The Digital Audio/Video Decoder: This complex integrated circuit reconstitutes the compressed data on the disc, converting it into studio-quality video and CD-quality audio for output to TVs and stereo systems.
Micro controller: This device controls the operation of the player, translating user inputs from the remote control or front panel into commands for the audio/video decoder and the disc reader mechanism. The micro controller would also be responsible for implementing parental lockout, dialing distributors for access codes and controlling decryption.
DVD Player Architecture
The Features of DVD-Video
Over 2 hours of high-quality digital video.
Support for widescreen movies on standard or widescreen TVs (4:3 and 16:9 aspect ratios).
Up to 8 tracks of digital audio, each with as many as 8 channels.
Up to 32 subtitle/karaoke tracks.
Automatic "seamless" branching of video (for multiple story lines or ratings on one disc).
Up to 9 camera angles (different viewpoints can be selected during playback).
Menus and simple interactive features (for games, quizzes, etc.).
Multilingual identifying text for title name, album name, song name, cast, crew, etc.
"Instant" rewind and fast forward, including search to title, chapter, track, and time code.
Doubles as a frisbee if the movie sucks.
Compact size (easy to handle, store, and ship; players can be portable; replication is cheaper).
Parental lock (for denying playback of discs or scenes with objectionable material).
Programmability (playback of selected sections in a desired sequence).
Random play and repeat play.
Compatibility with audio CDs, Video CDs, laserdisc and CDVs.
Component (YUV or RGB) output for highest-quality picture.
Six-channel analog output from internal audio decoder.
RF output (for TVs with no direct video input).
A disc has one track (stream) of MPEG-2 constant bit rate (CBR) or variable bit rate (VBR) compressed digital video. A restricted version of MPEG-2 Main Profile at Main Level (MP@ML) is used. SP@ML is also supported. MPEG-1 CBR and VBR video is also allowed. MPEG-2 progressive_sequence is not allowed, but interlaced sequences can contain progressive pictures and progressive macroblocks. In the case of 24 fps source, the encoder embeds MPEG-2 repeat_first_field flags into the video stream to make the decoder either perform 3-2 pulldown for 60 (59.94) Hz displays or 2-2 pulldown (with 4% speedup) for 50 Hz displays. In other words, the player doesn't really "know" what the encoded rate is, it simply follows the MPEG-2 encoder's instructions to produce the predetermined display rate of 25 fps or 29.97 fps.
Picture dimensions are max. 720x480 (29.97 frames/sec) or 720x576 (25 frames/sec). Pictures are subsampled from 4:2:2 ITU-R 601 down to 4:2:0, allocating an average of 12 bits/pixel. (Color depth is 24 bits, since color samples are shared across 4 pixels.) The uncompressed source is 124.416 Mbps for video source (720x480x12x30 or 720x576x12x25), or either 99.533 or 119.439 Mbps for film source (720x480x12x24 or 720x576x12x24). Using the traditional (and rather subjective) television measurement of "lines of horizontal resolution" DVD can have 540 lines on a standard TV (720/(4/3)) and 405 on a widescreen TV (720/(16/9)). In practice, most DVD players provide about 500 lines because of filtering. VHS has about 230 (172 w/s) lines and laserdisc has about 425 (318 w/s).
Maximum video bit rate is 9.8 Mbps. The "average" bitrate is 3.5 but depends entirely on the length, quality, amount of audio, etc. This is a 36:1 reduction from uncompressed 124 Mbps (or a 28:1 reduction from 100 Mbps film source). Raw channel data is read off the disc at a constant 26.16 Mbps. After 8/16 demodulation it's down to 13.08 Mbps. After error correction the user data stream goes into the track buffer at a constant 11.08 Mbps. The track buffer feeds system stream data out at a variable rate of up to 10.08 Mbps. After system overhead, the maximum rate of combined elementary streams (audio + video + subpicture) is 10.08. MPEG-1 video rate is limited to 1.856 Mbps.
MPEG2 Video Compression
MPEG2 (Motion Pictures Expert Group) encoding is a two-stage process, where the signal is first evaluated for complexity. Then, higher bit rates are assigned to complex pictures and lower bit rates to simple pictures, using an "adaptive," variable bit-rate process. The DVD format uses 4:2:0 component digital video compressed to bit rates with a range of up to 10 megabits per second. Although the "average" bit rate for digital video is often quoted as 3.5 megabits per second, the actual figure will vary according to movie length, picture complexity and the number of audio channels required . Picture quality approaches "D-1," the CCIR-601 TV studio production standard, 720 pixels per horizontal line vs. 320 pixels for VHS Tape. HDTV versions will have even greater resolution. As DVD is an optical format, the picture quality doesn't degrade over time and repeated use.
Because DVD-video is a disc-based medium rather than tape, it is possible for the player mechanism to seek to any place on the disc and begin playing. It can also pause, play in slow motion or fast forward easily, and with a much clearer picture than can a tape player. These random access features allow all manner of interesting applications, from multiple endings for a movie, to interactive video games, to multiple camera angles.
DVD manufacturers do not have to produce different versions of a film for both widescreen and pan and scan formats. The DVD format can contain 16:9, Letterbox and Pan and Scan formats on the same disk. The information for the cropping is contained on a separate track. This allows the viewer to select the format he or she prefers.
MPAA Rating Control and Multiple Film Versions
A single DVD disc can contain multiple versions of a movie with different MPAA ratings. This allows a viewer to select the version of the film he or she prefers.This feature also allows parental lockout, so that a child or other person, without the correct access code, could not view film versions above a certain MPAA rating. Furthermore, this feature allows certain countries to mandate that players sold in that country be outfitted with a chip which prohibits viewing of films above a certain MPAA rating. This eliminates the need to produce different versions of a film with different MPAA ratings for countries with content restrictions. When played, certain scenes will be skipped or alternative scenes shown according to the film version chosen.
DVD is able to store up to eight sound tracks (each with multiple channels), the format can support up to eight languages for a single movie. In addition, the format supports 32 closed caption tracks, for multiple language applications, for the deaf or any other commentary. LPCM format is mandatory, All other audio formats of DVD-Video (described below) will be optional.
Three sound formats of DVD:
Dolby Digital AC-3
48 or 96 kHz
Number of bits per sample
16, 20, 24bit
compressed (16 bits)
Compressed (16 bits)
Max transfer rate
Max Number of channels
5.1 or 7.1
There are two additional audio types supported by DVD-Video but both require additional external decoders to use the sound.
DTS (used in theaters)
SDDS (used in studio mixing)
All five audio formats support karaoke mode, which has two channels for stereo (L and R) plus an optional guide melody (M) channel and two optional vocal channels (V1 and V2).
Discs containing NTSC video (United States Standard) must use Linear PCM or Dolby Digital (AC-3) on at least one track. Discs containing PAL/SECAM video must use Linear PCM or MPEG-2 audio on at least one track.
The sample rate for Linear PCM can be as high as 96 kHz but most audio is sampled for DVD Videos at 48 kHz. The samples can either be uncompressed 16, 20 or 24 bits in size. DVD discs may have one to eight tracks of Linear PCM, but all audio channels combined can not exceed a bit rate of 6.144 Mega bits per second (Mbps). Effects such as shaping the sound so that it sound like a concert hall or cathedral or 3D sound for a spatial effect of synchronizing with the video on screen can be added within the extra sample data.
Dolby Digital (AC-3) form of Dolby Surround provides six discrete channels - right, left, center, right rear and left rear which are full bandwidth 20 to 20,000Hz and a discrete bass channel 20 to 120Hz for added bass effect. As a true digital system, Dolby Digital (AC-3) offers high quality sound, with outstanding dynamic range, vanishingly low distortion, wide frequency response and wow & flutter beneath the threshold of measurement. Sounds can be placed and moved anywhere in relationship to the listener; providing full 360 degree audio. As an option to Dolby Digital (AC-3) sound, DVD also enables producers to choose 16, 20 , 24-bit at either 48 KHz or 96 KHz, CD quality stereo sound with Dolby Pro Logic encoding.
MPEG Audio is multi-channel digital audio, compressed from original PCM format with sample rate of 48 kHz at 16 bits. It is the primary audio source for MPEG titles encoded in the PAL TV standard.
DTS is an optional multi-channel (5.1) digital audio format from Digital Theater Systems, compressed from PCM at 48 kHz. The data rate is from 64 kbps to 1536 kbps.
Sony Dynamic Digital Sound (SDDS) is an optional multi-channel (5.1 or 7.1) digital audio format compressed from PCM at 48 kHz. The data rate can go up to 1280 kbps.
Comparison to the other media
DVD vs. videotape... DVD blows videotape away with superior video and sound, instant search and rewind, durability.
DVD vs. digital videotape... Camcorders and VCRs using the new digital video (DV) cassette tape format are becoming available. DV compression is different from MPEG-2 and the quality is not quite as good.
DVD vs. laserdisc... DVD has the same advatages over laser disk such as as CLV LD (scan, pause, search) and CAV LD (freeze, slow) and adds branching, multiple camera angles, parental control, video menus, interactivity, etc. Unlike CAV LD, DVD can't play backwards, single-step backwards, or do bi-directional multispeed (until the players get more video memory). LD suffers from degradation inherent in analog storage and in the composite NTSC or PAL video signal. In numerical terms DVD has 345,600 pixels (720x480), which is 1.3 times LD's approximately 272,160 pixels (567x480). Widescreen DVD has 1.7 times the pixels of letterboxed LD (or 1.3 times anamorphic LD). As for lines of horizontal resolution, DVD ~= 500, LD ~= 425, and VHS ~= 240. ( All figures are for NTSC.)
DVD production has two phases: development and replication.
DVD-ROMs can be developed with traditional multimedia software tools such as Macromedia Director, Quark mTropolis, and C++. DVD-ROMs that take advantage of DVD-Video's MPEG-2 video and multichannel Dolby Digital or MPEG-2 audio require audio/video encoding.
DVD-Video development has three basic parts: encoding, authoring (design, layout, and testing), and pre mastering (formatting a disc image). The entire process is sometimes referred to as authoring.
Replication (including mastering) is usually a separate job done by large plants that also replicate CDs . DVD replication equipment typically costs millions of dollars. Most replication plants provide "one-off" or "check disc" services, where one to ten discs are made for testing before mass duplication.
Benefits of DVD
DVD is an agreed to, industry standard (In other words there will be no Mac, Windows, Betamax or VHS like wars). Developers will not have to worry about cross platform issues meaning that development budgets may actually decrease;
The increased capacity and extra data transfer rates mean that many of technical barriers (colour palette, quarter/half screen 15 fps video, etc.) confronting multimedia developers producing CD-ROM content will disappear with DVD. This should reduce the time to develop titles and the problems involved with cross platform issues. So DVD will become the high-performance platform for multimedia entertainment on the PC.