The New International CD-i Association

CD-i FAQ 2000 Edition

Section 5. Disc types

5.1 What is a CD-i disc?
A CD-i disc is a type of CD with audio, video and program content that can be played on a CD-i player. A CD may be called a CD-i disc only when it fully conforms to the CD-i Full Functional Specification, as laid down in the Green Book. When a CD-i disc does not fully conform to this specification (even if it can be played on a CD-i player, such as a Photo-CD or a Video-CD), it is not a CD-i disc. You can recognize a CD-i disc by its official logo that should be printed on the discs cover and on the disc itself. For more information about the CD-i system, the logo and the Green Book, refer to section 1 of this FAQ: The CD-i system.

5.2 What is CD-i Ready?
CD-i Ready is a special kind of CD-i disc. Following the rules from the Green Book, a CD-i disc may contain CD-Audio tracks. These should be placed after the CD-i track which is always track 1. However, on some older CD-Audio players, this CD-i track would be played back resulting in possible damage to equipment or speakers. To prevent this, the CD-i Ready format was defined. On a CD-i Ready disc, the CD-i program data (including all of its audio and video information) is stored in the pause sectors preceeding track 1. Usually, pause sectors preceeding track 1 are skipped by most CD-Audio players, but they can be read fine on a CD-i player. This allowed for a greater compatibility of CD-Audio discs which contained extra information when played on a CD-i player. In essence, a CD-i Ready disc is not a true CD-i disc, since it does not follow the rules of the Green Book for placing CD-Audio data, but they can be read correctly by all CD-i players ever produced.

CD-i Ready discs are usually music CDs (you can recognize these CDs by the indication CD-i Ready or CD-i Music in the upper left corner of the disc packaging), but they may also be other kinds of discs. For example, some games (most notably the games produced by SPC Group/The Vision Factory) are known to be in the CD-i Ready format. CD-i players equiped with the second generation player shell (refer to Comparison table of all Philips CD-i players on this site) may optionally play the audio-tracks of a CD-i Ready disc using the standard CD-Audio screen.

5.3 What is CD-Digital Audio or CD-DA?
Compact Disc Digital Audio is the official name of the original music CD. It was defined by Philips and Sony in the early 80s and its specifications were laid down in the Red Book. All CD discs and CD players should be in accordance with this specification to allow the bearing of the Compact Disc Digital Audio logo. This specification assures that every CD-Audio disc can be played in every CD-Audio player where-ever in the world.

The Green Book defines that any CD-i player should be able to play back CD-Digital Audio discs. For this, a CD-i player pops up a player shell when a CD-Audio disc is loaded in the player. This player shell allows for the direct selection of tracks, for programming Favourite Track Selections, for standard search options, etc. It's up to each manufacturer to decide what this player shell will look like and what features are offered, as long as all content of a CD-Audio disc can be played back on a CD-i player.

Look for the special note about CD-Extra (CD-Plus or Enhanced CD) in question 5.18.

5.4 What is CD+Graphics?
CD+Graphics or CD+G is an extension to the Red Book, defined by Philips and JVC. CD+G allows for the storage of simple graphics in the subcode channels of each sector on a CD-Audio disc. Each sector has 8 subcode channels combining 384 bits, resulting in 75 (sectors per second) x 384 bits = approx. 3.6 Kbyte per second. Due to this low bit rate, only very simple graphics can be stored. CD+Graphics can show 16 colors at one time on the screen, from a palet of 4096 colors in a resolution of 288x192 pixels. Any font that is used has to be encoded in the graphics stream as a graphical element. CD+G allows for the change of colors used on the screen, so that words can be highlighted for singalong purposes. CD+G is mainly used in Japan for karaoke-applications, and never gained much popularity outside this country. However, in Japan quite a few CDs were enhanced with CD+Graphics.

CD+G can be played on CD-Audio players with a Digital Output connected to a CD+G decoder, on most game consoles (like CDTV and 3DO) and on dedicated CD+G players. Although CD+Graphics is technically not related to CD-i, Philips included CD+G playback in all of its consumer CD-i players (CD+G playback is not included in the professional players CDI 180 and CDI 6xx series, except CDI 615). Note that also a very rare variant of CD+G exists, called CD+Enhanced Graphics. The extended graphics cannot be shown on a CD-i player, however the system is downwards compatible with CD+G.

A tool to create CD-Audio discs with CD+Graphics can be found on the Other CD-i tools page in the PC/Windows download section. With this tool, you can define a background picture for each track.

5.5 What is CD-BGM?
CD-BGM or CD-BackGround Music is a type of CD defined by Philips, Sanyo and Shinano-Kenshi in the mid 80s. Sometimes the system is being refered to as BMS (Background Music System). CD-BGM is used to store up to 10 hours of audio to use a background music in stores, shopping malls, etc. CD-BGM uses ADPCM level B mono audio to accomplish this. The music was stored in 8 tracks, all of which were devided in titles. Usually there were about 15 titles per track, resulting in about 120 songs per disc (about 8 hours). Although dedicated professional CD-BGM players were made available to play the discs (of which the Philips BMS 3000 was the most well-known), every CD-BGM disc also needs to include a CD-i application to allow for playback on a CD-i player.

It is not defined what features this application should include, as long it allows for the music to be reproduced on a CD-i player. This is why the early CD-BGM discs from Sanyo showed a screen devided in two halfs, with the upper half displaying 'start', and the lower half displaying 'stop'! Actually, these discs were the first commercially released discs for CD-i ever. Fortunately, Philips put some more attention to its CD-i application for CD-BGM. It show a list of all tracks that are available on the disc, which can then be selected for playback. Several hundreds of CD-BGM titles were made by Philips alone. Note: you cannot buy CD-BGM discs, they could only be 'rented' by professional users from selected Philips partners.

An article describing the history of CD-BGM and the features of Philips' CD-i application for CD-BGM discs is available in the Related Technologies section on this site.

5.6 What is a CD-i Bridge disc?
A CD-i Bridge disc is a CD-ROM/XA disc which includes a CD-i application for playback on a CD-i player. A CD-i Bridge disc is based on the ISO-9660 file system to allow for the usage on other platforms like PCs or Macintoshes. It is not obligated to store applications for other platforms, but they may be included on the disc. Usually, audio and video are encoded using CD-i encoding techniques like ADPCM for audio or MPEG for video.

Well-known examples of CD-i Bridge discs are Photo-CD, Karaoke-CD and Video-CD, but it is also allowed to use the CD-i Bridge disc 'specification' to make a dedicated disc type, as long as the disc is based on the ISO-9660 filesystem and it includes an application for playback on a CD-i player.

5.7 What is Video-CD?
A Video-CD is a compact disc with up to 75 minutes of VHS quality video with accompanying sound in CD quality. Audio and video are coded according to the MPEG-1 standard and the disc layout is based on the CD-i Bridge specification to allow for the playback on a variety of plackback devices like CD-i players and dedicated Video-CD players. The first version of the Video-CD spec was still called Karaoke-CD (see What is Karaoke-CD?) and was set up by Philips and JVC in 1993. Soon after followed the 1.1 spec, in which the name of the system was changed into Video-CD and the spec publishers were joined by Sony and Matsushita. Some years later, the 2.0 version added the ability to store still pictures on the disc and even allows for limited interactivity in the form of menu screens and selection items.

Video-CD became very popular mainly in Asia, as some 40 million Video-CD compatible players were sold by the beginning of 2000. Outside of Asia, Video-CD was mainly used as a prototype tool or as a cheap way to produce DVD-Video compatible discs. Although Video-CD compatibility is not required for DVD-Video players, it is very likely that Video-CD playback functionality is included since every DVD-Video player must be able to decode MPEG-1 as well.

For more information about Video-CD, the difference between Digital Video on CD-i and Video-CD, the various Video-CD versions, the various Video-CD applications for CD-i and other questions, please refer to section 6 of this FAQ: Video-CD on CD-i.

5.8 What is Karaoke-CD?
Karaoke-CD is the old name of the Video-CD standard. It dates back to 1993 when the standard was set up by Philips and JVC and the support of Sony and Matsushita was not yet there (they joined some time later when the name was changed into Video-CD). Karaoke-CD was -as its name already shows- mainly intented for karaoke applications in Japan. The system uses MPEG-1 audio and video, and is based on the CD-i Bridge specification. Therefore, Karaoke-CD is completely compatible with CD-i players among others.

5.9 What is Photo-CD?
The Photo-CD system was defined jointly by Philips and Kodak in 1991. The system allows for the storage of very high quality photographic images on a compact disc. The system is based on the CD-i Bridge specification to allow for the playback of Photo-CD discs on CD-i players, Photo-CD players (an overview of all Photo-CD players is available in the Related Technologies section of this site) and other systems.

Photo-CD was introduced as a complete consumer service product. Consumers were able to request for a Photo-CD when they brought their 35mm film to a Kodak photo-finisher for development. The resulted disc contained all of the photos in a variety of image resolution qualities. The disc could be returned to the photo-finisher to add more photo's, up to a total of slightly over 100 pictures. For this, the multi session feature was added to the CD-Recordable definition in the Orange Book.

The pictures on a Photo-CD a coded according to a Kodak-developed compression technique called Photo YCC. This algorithm makes use of the fact that the human eye is far less sensible for color differences than for changes in brightness in a picture. This reduces the size of a scanned picture from 18 MB to 3 to 6 MB per 'Image Pack'. Each picture is stored in an Image Pack, which containes one picture in 5 resolutions: Base/16 (192 x 128), Base/4 (384 x 256), Base (768 x 512), 4Base (1536 x 1024) and 16Base (3072 x 2048). These different resolutions can be used for a variety of purposes: the smallest ones can be used to produce a thumbnail overview on screen, the middle resolution can be used to show the picture in high quality on a TV screen, the 4Base resolution is used to zoom in on a particular area of a picture and the highest resolution can be used to make photographic quality prints. The latter one makes Photo-CD an excellent and durable storage medium.

5.9.1 What Photo-CD variants are available? Do they all play on CD-i?
Kodak and Philips defined 5 different variants of Photo-CD aimed at various types of usage. All of these types were based on the basic Photo-CD specification and are in accordance with the CD-i Bridge specification. All can be played on all Photo-CD compliant playback devices like a CD-i player.

Photo-CD Master
The 'regular' consumer Photo-CD, as the ones made by photo-finishers. A Photo-CD master contains pictures in up to 16Base resolution.

Pro Photo-CD Master
Pro Photo-CD is aimed at professional photographers. It allows for the storage of larger film formats than 35mm, for example 70mm. For this, an extra resolution is added to the Image Pack: 64Base which is 6144 x 4096. As a result, these images consist of 25.165.824 pixels, 32 times as much as the photos of a regular digital camera. A Photo-CD player and a CD-i player can play these discs in the regular way, however they make no use of this highest resolution.

Photo-CD Portfolio
A Photo-CD Portfolio disc contains images in up to Base resolution, which is perfectly suitable for display on a TV screen and still allow for zoom functionality. Photo-CD Portfolio is therefore used as a prerecorded medium to distribute large amounts of pictures (up to about 800) in a suitable way. A Photo-CD Portfolio may include sound in CD-Audio quality, pre-recorded playlists and even selection items on a photo which refer to other photos or playlists. These interactive features can be accessed on a Photo-CD player or a CD-i player when the appropriate CD-i application is stored on the disc.

Catalog Photo-CD
A Catalog Photo-CD only stores images up to Base resolution. This allows for the storage of several thousands of images in TV resolution. Catalog Photo-CD is rarely used.

Medical Photo-CD
Another professional Photo-CD variant, aimed at medical use. A Medical Photo-CD can be used for doctors to store CT or MRI scans for later reference.

5.9.2 What are the differences between the various Photo-CD applications for CD-i?
As a result of the CD-i Bridge specification on which Photo-CD was based, every Photo-CD must include a CD-i application to allow for the playback of the disc on a CD-i player. So far, Philips is the only company that produced such a CD-i application. A version of it is included with most Photo-CD authoring tools, and it is included on the Kodak PIW Workstation that is used by photo-finishers to make Photo-CDs.

Naturally, Philips continued to improve the performance and features of this application, that's why various versions of it excist. The version that is used on a particular disc is shown when the Exit-function is selected from the main menu. Although many interim versions excisted that were used internally within Philips, only a few of them were actually released to developers and Kodak. The most important of them were:

Version 1.x
The first version of the CD-i application for Photo-CD had a somewhat clumsy layout, and used rather small buttons that were placed on screen all at once when the menu was recalled. It allowed for the programming of photos in any other, for the rotation of pictures, and for zooming at a fixed zoom factor. Furthermore, it could show an overview of pictures on the disc on a thumbnail screen.

Version 2.3
As from version 2 onwards, the style of the on screen displays and the over-all look of the application was drastically changed. The menu that is shown on screen when a photo is displayed now only displays the main functions, an extra menu can be recalled to access the zoom function and the high/low resolution switch. This switch was added to speed up the loading of an image. This high/low res setting was valid for all Photo-CD discs (with this version of the application) that were loaded in a particular CD-i player. This 2.3 version was bundled with version 3.0 of the Kodak PIW Workstation software for photo-finishers that was released in late 1992.

Version 3.1
Version 3.1 added some major functionality and improved permormance compared to 2.3. To start with, it supports playlists and the playback of audio as defined for Portfolio Photo-CD. This allowed CD-i users to acces the limited interactive features offered by this disc type. The load of an image can be interrupted by the user, and new images are displayed with a top to bottom wipe on top of the previous image, without clearing the screen black at first. The low or high resolution setting is now remembered per individual photo. This 3.1 version was bundled with version 4.1 of the Kodak PIW Workstation software for photo-finishers that was released in August 1993.

Version 3.2
Version 3.2 includes some performance enhancements to allow for faster generation of the index thumbnail screen. It was the latest commercially released version of the application.

It is clear that a Photo-CD with version 3.x of the CD-i application offers a great improvement in terms of usability and performance. If you plan to make Photo-CDs, make sure that this version or later is included with your authoring package. There was also a version 3.2.1 of the Photo-CD on CD-i application, which allowed for a variable zoom factor, allowing you to zoom in at a very small area of a picture. Since this version is never released to Kodak, Photo-CDs with this version of the CD-i application are very rare.

As an alternative, a small (63 KB) single file application for CD-i players exists. It does not allow for favourite picture selection, nor does it support playlists, but it allows you to use a variable zoom factor to zoom in on a small area of the picture.

The latest commercial release of the Photo-CD on CD-i application (3.2) as well as the alternative application are available for download at the CD-i Application Downloads section on this site.

A document explaining how to use all menu functions of Philips' Photo-CD on CD-i application 3.x can be found in the CD-i Technical Documentation / Software section on this site.

5.10 Will CD-i play Picture-CD?
There are two completely different systems available currently, both of which are called Picture-CD. One is defined by Kodak, the other one by Corel and Adaptec. A Kodak Picture-CD is used in the same way as a Photo-CD, but the file format is different, and an application for Microsoft Windows instead of CD-i is stored on the CD. As a result, a Kodak Picture-CD is not compatible with Photo-CD players or CD-i players.

However, there are plans to make Kodak Picture-CD compatible with Video-CD 2.0 compliant players like Video-CD players, DVD-Video players and CD-i players by including all pictures as an MPEG still on the disc as well. The Nero Burning Rom CD-R authoring package from Ahead GmbH is known to support this feature from version 5.0 onwards, and it includes a compatible CD-i application to show the pictures in high resolution on TV using a CD-i player (see question How can I play my pictures on my CD-i player? for more info). Please note that Video-CD or CD-i compatibility is not a mandatory requirement of a Picture-CD, and hence can not be guaranteed. It is very likely that Kodak will replace the Photo-CD creation service of its photo-finishers with a Picture-CD service.

The other Picture-CD variant is defined by Corel for its Corel CD Creator CD-R package, and was later adapted by Adaptec when the product was sold to this company and renamed into Adaptec Easy CD Creator. An Adaptec Picture-CD is a type of disc with images in Kodak Photo-CD format, but the files are not placed at the sector locations specified by the Photo-CD specification, required files are missing and a CD-i application is not available. Hence, an Adaptec Picture-CD cannot be played on a Photo-CD player or a CD-i player. Adaptec is likely to use this strategy to bypass the expensive license fees from Kodak.

5.11 Will CD-i play CD-ROM discs?
The term CD-ROM is used for all types of usage of a CD in computer applications. A CD-ROM can contain various filesystems (like ISO-9660, Joliet, Apple HFS, Unix, etc.) or programs for a wide variety of computer systems (Microsoft Windows, Apple Macintosh, Linux, Free BSD, Solaris, BeOS, etc.). A CD-ROM that was made for one particular operating system, cannot be used on another system. There is no such thing as the "CD-ROM system". The difference between the CD-ROM specification in the Yellow Book and all other CD-systems is that only the physical sector format is defined, and not the application of a disc. Hence, a CD-ROM can only be played on a CD-i player when a CD-i application program is stored on the CD. In this case, a CD-ROM is called a CD-i Bridge disc (see What is a CD-i Bridge disc?), but usually these kinds of CDs are not called CD-ROMs on the discs packaging.

5.12 Will CD-i play Sony Electronic Book (Data Discman) titles?
Sony sold a portable playback device in 1991 called Data Discman. It accepted 8 cm CDs in a cartridge, which contained information in the form of text and very simple graphics. The application to show this information on the built-in black and white LCD screen was build in the player. These so-called Electronic Books were used for travel guides, dictionaries and other kinds of information that can be used on the road.

When Sony first announced Electronic Book, they promised to make the system CD-i compatible in the near future. For this, a CD-i application would be included on the discs. But some years later, Sony officially announced to Philips that this was not going to happen. This announcement was never made available to general public. Hence, an Electronic Book disc cannot be played on a CD-i player.

5.13 Will CD-i play Super Video-CD?
Super Video-CD is an extension to the Video-CD specification, set up by the original Video-CD licensees (Philips, Sony, JVC and Matsushita) in 1999. Super Video-CD uses DVD-quality MPEG-2 video on a standard CD which runs at variable bit rates up to double speed (2.8 kbps). This allows for 35 to 70 minutes of high quality video on a regular CD. Super Video-CD is a cheap way of making discs that are playable on compatible DVD-Video players using a regular CD-Recorder.

Since Super Video-CD uses MPEG-2 video compression instead of MPEG-1 that is used in CD-i, and because of the fact that the disc can be played up to double speed of which a CD-i player is not capable, a Super Video-CD cannot be played on a CD-i player. Therefore, the CD-i application that is mandatory for Video-CD is not available on a Super Video-CD.

5.14 Will CD-i play Super Audio-CD?
Super Audio-CD was introduced by Philips and Sony in 1999 as the succesor of the popular Audio-CD. The system uses a new audio encoding technique called DSD (Direct Stream Digital), which comes way much closer to the original analogue audio quaility than PCM which is used for regular Audio-CDs. To store the large amounts of data that are needed for DSD, a Super Audio-CD uses a DVD-like high density disc.

One of the great features of Super Audio-CD is that is allows for a CD-compatible data layer on a disc. When such a CD layer is available on the disc, it can be played on any CD player, including a CD-i player (in standard CD quality of course). Please note that this CD-Audio layer is a producer's option, and is not required for any Super Audio-CD. Only discs with this CD-compatible layer can be played on a CD-i player. Look for this information on the CDs case.

5.15 Will CD-i play HDCD, CD-Video, CD-MIDI or CD-Text?
HDCD (High Density Compatible Digital) is an extension to CD-Audio which raises the bit depth of the sampes from 16 to 20 bits, allowing for a higher sound quality on players with a HDCD decoder. Any HDCD-CD can be played on any CD-player, including CD-i players. To date, no CD-i player makes use of this extra HDCD-information.

CD-Video (not to be confused with Video-CD, which is a totally different system) is a 12 cm CD which contains 20 minutes of CD-Audio and up to 6 minutes of LaserDisc-format analogue video. The video can only be played on LaserDisc players, the audio can be played on any CD-player, including CD-i players.

CD-MIDI is a CD-Audio disc with MIDI (Musical Instrument Digital Interface) information in the subcode channels. This allows for MIDI-devices like synthesizers to play along with the music on the CD. The applications of CD-MIDI are very rare. The audio of a CD-MIDI disc can be played on any CD-player, including CD-i players.

CD-Text is a CD-Audio disc with the names of songs and performers stored in the subcode channels. This information can be made available on the displays of compatible CD-players. It is very likely that all future CD-Audio discs will contain CD-Text information. To date, no CD-i player will display CD-Text information. The audio of a CD-Text disc can be played on any CD-player, including CD-i players.

5.16 Will CD-i play DVD discs?
No. A DVD is a different kind of disc, based on a high density format. It requires a new physical laser unit to read the discs. A CD-i player can only read discs based on the normal infra-red laser technique: compact discs or CDs. It is unlikely that a combination playback device for CD-i and DVD will ever become available, nor will it be possible to upgrade a CD-i player to play DVD discs since this should require the replacement of the entire disc read-out mechanism.

5.17 Will a DVD-player play CD-i discs?
A DVD-Video player cannot play CD-i discs, since it does not include all of the CD-i logics such as the required operating system in ROM, the CPU and the appropriate audio and video decoding ICs. Most DVD-Video players however can play Video-CDs, but they use an internal playback application instead of the CD-i application that is stored on every Video-CD disc. Hence, CD-i specific additions such as menu screens or subtitles will not be shown.

A DVD-ROM drive is physically able to read CD-i discs, but since a normal PC is unable to play CD-i titles, you won't be able to run them. Refer to section 9 of this FAQ: CD-i on other platforms for more information.

5.18 I'm having troubles playing a CD-Extra (CD-Plus, Enhanced CD). Why?
A CD-Audio disc may contain data tracks, for example containg CD-ROM programs with additional info about the performing artist. However, when such a disc is played on an old CD-Audio player, the data track would not be recognized as such, resulting in the playback of noise. Playing this noise loud could eventualy result in the damaging of the speakers.

To avoid this problem, Philips, Sony and Microsoft established a standard which was initally called CD-Plus but which was later renamed into CD-Extra due to trademark-related issues. Sometimes it's also called Enhanced (Music) CD. The logo is made up of the regular CD-Digital Audio sign with a '+'-mark next to it. The standard is described in the Blue Book.

Such a CD-Extra is a so called "stamped multi-session" disc. It is in essence a multi-session disc like the ones you can create with your CD-Recorder, with the music in session 1, and the data in session 2. Every ordinary CD-Audio player can only read the first session and it will play the music without the risk of playing back the noisy data. A computer with a multisession CD-ROM drive (all drives manufactured after 1992) can access the data in a normal way. And this is were the CD-i "problem" comes in: since virtually all CD-i playes (with the exeption of some older professional models) contain a multi-session drive, the player reads the latest session (which it is supposed to do according to the multi-session specification) where it wouldn't find any CD-i data nor audio-tracks. As a result, the disc will not play. The CD-i player is too smart to fall for the CD-Extra trick! This problem can not be solved in any way :-(

Remeber that a CD-i player can play the CD-Audio tracks of CD-ROM discs that contain the CD-ROM data as a regular track. Look for the CD-Extra (CD-Digital Audio+) logo on a disc to verify wether it is a true CD-Extra disc and hence not usable on a CD-i player.

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