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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 “Compact Disc Interactive” 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 as audio, 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 preceding track 1. Usually, pause sectors preceding track 1 are skipped by most CD-Audio players, but they can be read on a CD-i player. This allowed for the creation of CD-Audio discs which contained extra information when played on a CD-i player, with the least amount of playback issues when the disc is played in a normal CD-Audio 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 the placement of CD-Audio data, but they can be played 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 equipped 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, hence not needing to run the CD-i application on the disc.

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 for the inclusion of the Compact Disc Digital Audio logo. This specification assures that every CD-Audio disc can be played in every CD-Audio player anywhere 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 includes a player shell that is displayed on screen 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.

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. Subcode channels are a mandatory part of every Audio-CD. Apart from addressing and timing data, in most cases they don’t contain extra data. As a result of this, CD+G data in the subcode channels does not take up additional space on the disc, nor does it affect the normal playing time of a CD.

Each sector has 8 subcode channels combining 384 bits, resulting in 75 (sectors per second) x 384 bits = approx. 3.6 Kbytes 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 palette 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 changing 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 some 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 (CD+EG). The extended graphics cannot be shown on a CD-i player, however the system is downwards compatible with CD+G.

Note that in order to create a CD+Graphics disc, the CD-recorder must be able to write subcode data (not all CD-recorders will support this).

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 referred to as BMS (Background Music System). CD-BGM is used to store up to 10 hours of audio for the purpose of playing background music in stores, shopping malls, etc. CD-BGM uses ADPCM level B mono audio to accomplish this. The music is stored in 8 tracks, all of which are divided in titles. Usually there are 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 as 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 divided into two halves, with the upper half displaying 'start', and the lower half displaying 'stop'. Depending on the strictness of your definition, 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 shows a list of all tracks that are available on the disc, which can then be selected for playback. Hundreds of CD-BGM titles were made by Philips alone. CD-BGM discs were not offered for sale, 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 to allow for the playback of the disc on a CD-i player. A CD-i Bridge disc is based on the ISO-9660 file system that is supported by most platforms like PCs or Macintoshes. It is not a requirement to include applications for other platforms besides CD-i, 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, using CD-i's mode 2 form 2 sector format, whereas data is stored in mode 2 form 1 sectors. This makes CD-i Bridge (or CD-ROM/XA) discs different from regular CD-ROMs, which usually store all of their information in mode 1 sectors.

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 discs that do not conform to either one of these disc formats, as long as the disc is based on the ISO-9660 file system 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 playback on a variety of playback devices like CD-i players, some game consoles, dedicated Video-CD players and most DVD-Video and Blu-ray Disc players.

The first version of the Video-CD spec was 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 high resolution still pictures on the disc and it specified limited interactivity in the form of menu screens and selection items.

Video-CD became very popular mainly in Asia. Outside of Asia, Video-CD was mainly used as a prototype tool or as a cheap way to produce DVD-Video playable 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 defined 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 and the version number of the spec was increased to 1.1). Karaoke-CD was -as its name already says- mainly intended for karaoke applications in Japan. The system uses MPEG-1 audio and video, and is based on the CD-i Bridge specification. Therefore, Karaoke-CDs are playable on CD-i players.

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 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, dedicated Photo-CD players (an overview of all Photo-CD players is available in the Related Technologies section of this site) and other systems including some game consoles.

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 resulting 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 photos, up to a total of slightly over 100 pictures. For this, the multi session feature was added to the CD-Recordable specification in the Orange Book.

The pictures on a Photo-CD are encoded according to a Kodak-developed compression technique called Photo YCC. This algorithm takes advantage of the fact that the human eye is far less sensible to color differences than to 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 contains 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 made 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, 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. A Photo-CD player and a CD-i player can play these discs in the regular way, however they make no use of this extra resolution.

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

  • Medical Photo-CD
    Another professional Photo-CD variant, aimed at medical use. A Medical Photo-CD can be used by medical professionals 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?
    Conforming to 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. Philips was 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 was 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 exist. 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 existed 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 called up. 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
    From version 2 onwards, the style of the on-screen displays and the overall 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 called up 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 persistent for all Photo-CD discs (with this version of the application) that were loaded in a particular CD-i player, as the user’s setting was stored in the player’s NV-RAM. 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 performance compared to 2.3. It supports playlists and the playback of audio as defined for Portfolio Photo-CD. This allowed CD-i players to access the limited interactive features offered by this disc type. The loading 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 to black 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 were also 3.2.1 and 3.3 versions 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 these versions were never used by Kodak on consumer Photo-CDs, 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. It was used for internal purposes within Philips.

    The latest commercial releases of the Photo-CD on CD-i application (3.2 and 3.3 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?
    Various types of CD-ROM discs containing pictures were called 'Picture-CD'. Among the most used ones is one is defined by Kodak, and another 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.

    Some 'Picture-CDs' are 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. The Nero Burning Rom CD-R authoring package from Ahead GmbH was 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 playback on Video-CD or CD-i players can not be guaranteed.

    Another Picture-CD variant was 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.

    5.11 Will CD-i play CD-ROM discs?
    The generic term CD-ROM is used to indicate 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, game consoles, 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 track layout, physical sector format and error correction is defined, and not the application of the 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 disc's 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 used 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 stored 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. To accomplish this, a CD-i application would be included on the discs. In reality this never happened. 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, defined by the original Video-CD creators (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 CD speed (2.8 Mbps). 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, by 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 are 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 also not included 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 a high-end successor to the popular Audio-CD. The system uses an audio encoding technique called DSD (Direct Stream Digital), which resembles the original analogue audio quality more closely than PCM encoding, 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 4.7 or 8.5 GB high density disc.

    Super Audio-CD optionally supports the inclusion of 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). Please note that this CD-Audio layer is a producer's option, and is not a requirement for Super Audio-CDs. Only discs with this CD-compatible layer can be played on a CD-i player. CD-Audio compatibility is indicated on the Super Audio-CD’s packaging.

    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 samples from 16 to 20 bits, allowing for a higher quality sound playback on players or A/V receivers with an HDCD decoder. The extra information is stored in the subcode channels of the CD, this data is ignored by any player that does not specifically support HDCD.HDCD was not developed by Philips and Sony, and it is not related to or part of the Red Book CD-Audio specification. Currently, the technology is owned by Microsoft.

    CD-Video (not to be confused with Video-CD, which is a totally different system) is a 12 cm CD that contains up to 20 minutes of CD-Audio tracks and up to 6 minutes of LaserDisc-format analogue video with accompanying digital audio. The video track can only be played on LaserDisc players, the audio-only tracks 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, like car audio units. CD-i players can not 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 different physical laser unit based on red laser technology to read the discs. A CD-i player can only read discs based on CD-standard infra-red laser technique.

    5.17 Will a DVD-player play CD-i discs?
    A DVD-Video player cannot play CD-i discs, since it does not include CD-i components 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.

    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 to store programs with additional info about the performing artist that can be shown on a computer platform. However, when such a disc is played on an older generation CD-Audio player, the data track might not be recognized as such, resulting in the playback of noise.

    To avoid this problem, Philips, Sony and Microsoft established a standard which was initially 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 specified in the Blue Book.

    Such a CD-Extra disc is a so called "stamped multi-session" disc. It is in essence a multi-session disc (specified in the Orange Book CD-Recordable standard, and originally developed to store pictures in multiple sessions on a Photo-CD), with the music in session 1, and the data in session 2. Every ordinary CD-Audio player can only read the first session of a multi-session disc, and consequently it will only 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 stored in the additional session on the disc.

    And this is where the CD-i "problem" comes in: since all consumer CD-i players and all later generation professional CD-i players contain a multi-session capable drive, and according to the multi-session specification the player will read the latest session first. Since this is the session where the data with the extra information for playback on a computer platform is stored, it will not "see" the audio-tracks. As a result, the disc will not play. Remember 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 on normal “single session” CDs. Look for the CD-Extra (CD-Digital Audio+) logo on a disc to verify whether the disc is a true CD-Extra disc and hence will not be usable on a CD-i player.

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