The purpose of this report is to give some guiding and to be technological starting point for distribution of CD or DVD disc. I don’t cover the distribution and packaging, just mastering and replication.
There are several books and articles written on CD and DVD production. Very few are on the topic of discs with mixed content (video and software), and most are targeted towards small volume projects. I have interviewed some people in the business and made some conclusions from this.
This text was originally produced as internal report on CD and DVD production for IKEA. It was written in august 2004 so some fact may have changed during those years.
* Images has been deleted due to copyright issues.
CD and DVD technology in brief
The DVD is in many ways an evolution from the CD. From a user perspective it can be seen as a high capacity CD. From a technical and manufacture perspective they belong to the same family, but even family members can be very different. The technology can be divided in a hard and a soft part. The hard part describes how data is physically stored on the disc. The soft part, how data is encoded and organized.
The hard side
CD and DVD store data in spiral tracks of groves on a reflective layer. A laser pickup recognizes the transition between land and grove, and this is decoded as data bits (0 or 1). A DVD stores more data on the same area compared to the CD. This is possible through two enhancements over the CD. The first is to use smaller groves and a “thinner tracks”. The DVD has about half the track spacing and about half the grove size. The second difference is that a DVD can have several layers, and that layers of CD and DVD are at different depth of the disc.
* Illustration from p 76 of “DVD Demystified” by Jim Taylor
A CD contains one reflective layer that is located at the top (just under the label) of the disk. A DVD has up to four reflective layers in the middle of the disc. Two layers can be read from the same side. The outer layer is then semi-reflective. The inner layer is read through the outer by changing the focus of the lens system. Just like you can see through a fence. A double-sided disc must be manually turned by the user, this makes them awkward. Normally a video DVD has two layers that are read from the same side (DVD-9). Shorter videos or data DVD (DVD-ROM) are normally single side single layer (DVD-5)
* Illustration from p 78 of “DVD Demystified” by Jim Taylor
All DVD players can read CD:s, while a standard CD-player can’t read a DVD.
The driving force in the DVD development was to squeeze in a full length movie without the need to turn the disc. Some space is needed for error correction, file structure, headers etc. How much depends on the content type, but 5-20% is a common. It’s possible to reduce the track spacing and gain more capacity. This is how 800 MB CD is implemented. 1 hour of average video takes about 2 gigabyte on a DVD.
|Type||Sides||Layers||Data Capacity GB|
There are recordable CD and DVD discs. The disc contain a dye layer in front of the reflecting layer. A strong laser modifies this dye layer to record data. On a rewriteable disc this dye layer can also be restored to original state, so the disc can be reused. Recordable discs are a convenient way to store, backup and transport large volumes of data. CD-writers are today standard, and many computers are today shipped with DVD-writer. Rewritable DVD is still uncommon, but DVD-RW is soon expected to be available.
CD-R Recordable CD
CD-RW Rewritable CD. Need special writer, disc must be erased after rewrite.
DVD-RAM First type of rewritable DVD. Can’t be used in all DVD-players, and disc is normally kept inside a cartridge. Normally only used for backup and data transfer. Can be double sided.
DVD-R The most common type of recordable DVD
DVD+R Competing format with DVD-R. Some drives accept both DVD-R and DVD+R
Disc-at-Once vs Track-at-Once — Most CD-recorders only support Track-at-Once. They make a short pause in between tracks leaving a few blank sectors. This may result in clicks on some CD-players. For professional use (specially for mastering) Disc-at-Once should be used, which means that the whole CD is burnt without those pauses.
The soft side
The Latin alphabet can be used as a hardware layer for many languages. Just because we use the same letters doesn’t make us understand all languages that uses Latin letters. There are several standards for how to encode and organize data, sound and video on a CD or DVD. Some players support many formats, but there are many odd features supported by only a few.
There main content types are audio, video and data. The original CD format was audio only and is described in the Red Book standard. Later standards evolved for video, data and still pictures. Today many discs contain a mix of those content types. But special care must be taken to make the disc playable in both computers, DVD-video and music players.
|Type||Content||Note / Standard|
|CD-DA||Normal audio CD||Red book|
|PhotoCD||Photographic images||Playable in computer, Video CD and DVD-players|
|VideoCD||MPEG-1 compressed video||Old standard that are a base for DVD-video.
Rarely used due to the limit of 74 min / disc. White book and CD-I
|CD-ROM||Data content (software, pictures, games…)||Normally only to be used in a computer. But
some audio players can handle MP3 audio tracks on this format.
|CR-ROM XA||Mixed content (data, video, audio)||Can be used in audio players and computers.|
|DVD-Video||MPEG-2 compressed video||Standard DVD movie disc|
|DVD-ROM||Data content (software, pictures, games…)||Can also contain Video and Audio tracks playable
by normal DVD-players
|DVD-Audio||High quality audio|
Video are always compressed, the standard format is MPEG-2. Normal audio discs are not compressed, but it’s getting common with players that handle MP3 compressed audio. Without compression it would be impossible to squeeze a full-length film on a DVD.
A CD/DVD can be used even with a scratched surface. The scratches are out of focus to the beam (looking through the fence). This means that data can be read without problem through small scratches. With larger defects we lose some data bits. By encoding the data in a way that missing bits can be calculated from the surrounding data means that small read errors can be fully corrected. The error correction uses about 13% of the disc space.
CD-ROM/DVD-ROM usually lacks error correction code, and more sensitive to scratches.
This file system organizes how files are stored on the disc. A file doesn’t have to be a continuous area on the disc. Often several files are interleaved so that audio, video and data can be read continuously without moving the pickup. The file system can be seen as a librarian that organizes the content and tells where to find what.
Audio CD (CD-DA) has a very basic file system specified in the Red Book
The most common file system format on CD-ROM is ISO 9660, also called HSF High Sierra File Format. There are extensions on this standard that states how different operating systems should store extra data (icons, privileges, type). This is slowly being phase out and replaced by UDF.
UDF Universal Disc Format (ISO 13346:1995) is more modern file system. DVD-ROM can use ISO 9960 or UDF. DVD-Video should use UDF. There is a format called UDF-bridge that is a UDF format that is backward compatible with ISO 9660.
There are special requirements on a Video DVD that states how video, audio and menu data must be organized. There are extensions in the UDF-format that states how operating system specific data should be organized.
Audio CD and CD-ROM standard doesn’t state implementation of copy protection. The methods used by the music industry are not part of the standard.
The DVD-Video standard supports three forms of protection; antitaping protection, copyright information and information scrambling. A part of this is a regional code that tells in what region the disc may be sold. The film industry demanded those protections. But there is of course nothing preventing you to produce an unprotected disc that can be played in all regions…
A DVD-video disc contains a menu system to let the viewer select language and other features.
The production can be divided in three steps (after planning and creation of content off course), pre-mastering, mastering and replication (duplication). With small volumes the discs are duplicated with a robotized CD/DVD-writer and a robot. For volumes above about 500 disc the disc are replicated by molding.
Pre-mastering is the step before serial production. Video is compressed and encoded, sound and voice tracks added, subtitles and graphics are added, menu systems created, files sorted in a layout that gives good playback performance. Special authoring software is used for those steps. Then the content is written to a CD-R/DVD-R, or stored at a DLT tape.
Larger volumes are produced by replication where the disc is molded. This requires a sophisticated molding and sputtering equipment. Mastering is the process where the stamping form is created. A glass master is exposed with a laser. A DVD-R/CD-R can be used as original for this process. The stamper is created from the glass master by electro forming. One stamper per layer is needed. Several stampers are used for large volume replication.
* Illustration from p 121 of DVD Demystified by Jim Taylor
The disc is then replicated by molding plastic with the stamper. Reflective coating is sputtered on the plastic. In case of dual layers a new plastic or lacquer layer is formed on top of the first. A DVD consists of two molded halves that are glued together so that the layers are at the middle of the disc. A CD is only one peace is molded and then that is covered with lacquer. The label is printed with screen or offset. Discs are delivered on spindles or in final package.
The process of CD and DVD replication is similar and some systems can produce both types. But CD replication is a simpler process since it has courser feature size and only need one molting step.
* Illustration from p 121 of DVD Demystified by Jim Taylor
Getting a price on large volume DVD production is a bit tricky without making an official quota request. But at these volumes the mastering cost is negligible. The price for 25 000 copies of a DVD-5 disk with 5-color printing, without packaging is about $0.54 per disc (source www.dvdtransfer.com). There is a 13% difference on the per copy price between 25 000 and 50 000 copies. I spoke with people at the DVD and CD manufacturer SDC Group and on a 5 000 copy offer a CD-ROM is about half the price of a DVD-5 disc (5.00 SEK vs 9.95 SEK). If we could use a CD-ROM with maximum 600 MB it should be possible to get below $0.30 per disc when produced in USA or Europe. There is large CD replication sites in Asia that should be able to give even lower prices.
Standards and Vocabulary
The different standards that regulates CD and DVD formats are a jungle. Here is a short list of the most common references you find.
Red book (CD-DA)
The original audio standard also called CD-DA. This is a standard music CD. It can only contain uncompressed PCM coded sound. This format can be played in all CD, CD-ROM and DVD players. It uses a very simple error correction mechanism, CIRC (Cross-Interleaved Reed Solomon Code) can correct minor scratches in the disc surface. The sector format has a longer data block (2352 bytes) than all other formats. Multi session write is not supported.
Data disc standard for standard CD-ROM
The standard is divided in 4 layers.
Layer 0 – Bit structure (identical to Red book).
Layer 1 – Sector layout (mode 1 or 2).
Layer 2 – Logical sector organization.
Layer 3 – Logical file organization (normally ISO 9660).
There is an extension called Mixed-mode that allows coexistence of Red book audio and Yellow book data on the same disc.
Another extension is the CD-ROM XA that allows synchronized playback of audio, video and data. This multi media format is popular for game and education content. Two different sector formats are allowed. Mode 1 sector format includes synchronization and localization headers. It has contains advanced error correction features. This only leaves 2048 bytes for data (out of 2532 bytes). Mode 2 has the same sync and location headers but only CIRC error correction. Each sector carries 2324 bytes of data. Mode 2 should only be used in applications where some data loss is accepted, but gives higher data rate.
ISO 9660 / HSF file format
The HSF (High Sierra File Format) is a platform independent file system that defines the logical structure of data. This is the basis for the ISO 9660 standard. CD-ROM with data files should use this file format. There are extensions to this that declares how to handle operating system specific parts (for Mac, PC, UNIX). But in general there is today only small problems making them co-exist.
UDF Universal Disc Format
File format used by DVD-Video, and many CD-ROM and DVD-ROM. Standard ISO 13346:1995. There is a UDF-bridge format that are backward compatible with ISO 9660.
Green Book (CD-I)
Multimedia disc standard that allows audio with synchronized text. MPEG-1 and MPEG-2 video with multiple language tracks. Many players can play this standard, but it never got any broad commercial success. A CD-I compatible player can also play PhotoCD and VideoCD disks.
The orange book standard defines multi session volumes. The content of a writeable (CD-R, CD-RW) may be written at several different times in a successive order to the disk. Some older drives may have trouble reading multi session disks if the disk has not been closed. Before closing the disk contains no directory table, this is written when the disk is closed for further writing.
The white book standard defines an environment where CD-ROM XA, CD-I, PhotoCD and VideoCD can coexist. It permits a number of different data sets to be exchanged in a convenient way. It only support 74 minutes of video. This limits it use for film distribution, except for shorter instruction, music or commercial videos. You can se this as an umbrella standard covering the Red, Yellow, Green and Orange book standards.
Standard music playback + multimedia
DVD Demystified by Jim Taylor
CD-R/DVD Disc Recording Demystified by Lee Purcell