IIMS 92 contents
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Compact disc interactive (CD-I): A multimedia system of the future

Neil A. Shaw & Graham J. Standfield
Computer Aided Learning Centre
Victoria University of Technology


Compact disc interactive (CD-I) refers to a multimedia technology with a range of attributes which have been designed to appeal to the home consumer market as well as industry and education. Philips, Sony and Matsushita have developed this new CD-I standard as a natural extension of their highly successful CD-Audio system. The 12 cm, CD-I discs contain audio, text, graphics, photographic images, animations and video; audio is delivered to a normal amplifier or hi-fi system, and visuals are displayed on a normal television monitor. Interactivity is provided by a hand held remote control device which enables the user to steer a cursor over images on the monitor and select menu items or other icons and "hot spots" made available by the program design.

The Computer Aided Learning Centre at Victoria University of Technology invested in this technology in 1990. By acquiring the appropriate hardware and software tools we have been able to assess the system, to build CD-I products, and to offer a service to industry and educational institutions seeking to have programs developed on the CD-I platform.

The aim of this paper is to describe some of the attributes of the CD-I system, to outline some of the processes and issues involved in creating a CD-I title, and to describe our experiences in making Australia's first CD-I disc.

The CD-I system

A CD-I delivery system or player is based on the 68070 chip with data management under the control of the Compact Disc Real Time Operating System (CD-RTOS), a derivative of the OS9 Operating System. Packaged as a single closed system, the computing power of a CD-I player is dedicated to decoding and reproducing sound and image information from a compact disc, and responding to user input from the input device. Players are commercially available for about $US800.

The capacity of a CD-I disc exceeds 600 Megabytes, which is shared across the text, audio and image data files. To further illustrate the storage capacity of the disc, the following comments refer to dedicated space for each medium:

Text only: A disc could hold over 120 million words or more than a 20 volume encyclopedia, and with encoding this could be increased to 300 million words.

Audio only: A disc can hold a maximum of 19.5 hours of mono audio or 72 minutes of high fidelity stereo CD digital audio.

Images only: CD-I enables images to be stored in a variety of formats, including DYUV coding, uncompressed 15 bit RGB and 8 bit RGB images, CLUT (colour look up table) images, and graphics, which are simply run length encoded. Individual file sizes of images vary according to which of these formats are used, with as little as 10 kByte needed for a run length encoded graphic.

A combined multimedia CD-I product must take into account this range of audio and image formats, with the aim of ensuring the right balance between sound/image quality, disc capacity, and the desired audiovisual effect.

Production of a CD-I title

The process of developing a CD-I title commences with the creative idea, a needs analysis and a suitable business plan, similar to any other multimedia project. A study of the target audience, story board development, instructional design and flow charting are normal steps which follow.

The next stage of collecting the multimedia assets, involves digitising original photographs, creating graphics and animations with appropriate paint packages or authoring systems, and recording the audio (voice and special sound effects). Although these assets can be created with any system, such as PC, Macintosh or SUN computer, the digitised sound and image data must be converted to CD-I formats and imported into the CD-I developer's platform (a special Philips system). In this process the audio and images are treated as follows:

Audio production

An analogue audio file recorded on tape in a studio is first digitised with an IBM compatible, Macintosh or SUN computer (at 44.1 KHz sampling rate). These data files are then converted into one of four CD-I standard audio formats, which the producer selects according to their instructional design, before being transferred to the CD-I system for authoring.

Options for the audio resolution include

  1. stereo, high fidelity (CD-Digital Audio) quality (16 bit resolution with 44.1 KHz sample rate),
  2. Level A, stereo or mono, (8 bit resolution, with 37.8 kHz sample rate),
  3. Level B, stereo or mono, (4 bit resolution, with 37.8 KHz sample rate),
  4. Level C, stereo or mono, (4 bit resolution, with 18.9 kHz sample rate).
The different sampling rates are used for appropriate effects and in accordance with some CD-I design rules for mixing images with audio.

Image production

Colour photographs can be scanned or captured with various frame grabber or flat bed scanner systems using any host computer. These files are then converted to CD-I format using appropriate software tools, with the final images exported to the CD-I developer's platform. Just like the case with audio files, these image files can have any one of several CD-I formats, depending on the desired effect.

Options for the image resolution include

  1. DYUV high resolution images (16 million colours, 16 bits per 2 pixels) used for natural images.
  2. RGB 555 images (32,000 colours, 16 bits per pixel) used for detailed images,
  3. CLUT 8 images (256 colours from a pallet of 16 million, 8 bits per pixel), used for graphics,
  4. CLUT 7 images (128 colours from a pallet of 16 million, 7 bits per pixel), used for graphics,
  5. CLUT 4 images (16 colours from a pallet of 16 million, 8 bits per 2 pixels), used for text
  6. RLE 7 images (128 colours from a pallet of 16 million, 7 bits per pixel), used for cartoon animation,
  7. RLE 3 images (7 colours from a pallet of 16 million, 8 bits per 2 pixels), used for cartoon animation.
Note that animations require images to be delivered at the rate of 16 frames per second. Since RLE 7 images are only 10 kByte in size, this means that animations can be achieved within the 176 kByte/sec data transfer limits of Compact Disc players.

One method of assembling and presenting these assets under program control is with the aid of special CD-I developers tools, including authoring systems such as "Media Mogul". Sequential presentation and integration of images, text and audio can be achieved then tested with such software. Our experience in developing CD-I products with these tools has been very positive and encouraging, and we have found that the authoring techniques are sufficiently versatile to enable us to quickly experiment with many different effects until desired outcomes have been achieved.

After developing the product on a large hard disk, a script to disc software package is used to create a CD-I disc image for emulation of the final product. This interim product is then tested to ensure that access rules are not violated and the timing sequences are within the CD-I specifications. This emulation process is an essential step prior to committing further resources to actually cutting a 12 cm CD-I disc. Finally a single WORM (Write Once Read Many) disc is burnt, using a Yamaha PDS machine (or soon the Philips equivalent) and tested in a normal CD-I player. Very low numbers of discs can be replicated in this manner, but a more efficient mass production process would require a master disc to be replicated at an optical disc pressing factory (like Distronics), in a manner similar to that used for other Compact Disc products, such as CD-ROM and CD Digital Audio.

An example product

The first CD-I disc designed and developed in Australia featured the Victoria University of Technology. After a brief introduction, this program displays a Main Menu of options, including an explanation of where the University is situated, the courses offered, faculty structures, and a Producers Corner. If a user selects the "Where" option from the Main Menu, the program branches to a sequence of images in which a camera zooms onto a world map until finally reaching a detailed map of Melbourne and its western suburbs. Background music and a narrator's voice accompany this process, and icons identifying each of our four campuses are superimposed on the final map. Using the remote control device, a user can then select any one of these icons and take an audiovisual tour of the corresponding campus. Options to explore more detailed information about the location of Melbourne, including distances from other Australian cities and selected cities in Asia, USA and Europe are also available.

Similarly the "Courses" option enables a user to interactively explore the range of undergraduate and postgraduate courses available at the University. Again the user can select icons to extract more and more details about a specific field of interest, rather than receive an overload of information about all courses.

As an experimental product, this CD-I disc does not have commercial value. However we are now experienced with most aspects of CD-I production and have commenced the process of creating programs which target home consumers world wide.


Compact disc interactive is a multimedia system with the potential to penetrate into industrial, educational, and home consumer markets throughout the world. Our initial commitment to this technology has resulted in an experimental CD-I disc which enables users to interactively explore the campus and courses of Victoria University of Technology. The process of developing this product has enabled us to assess the methodologies, software and hardware specific to CD-I technology. As a result of this project, we are expanding our interest and commitment to CD-I, as well as offering our expertise to colleagues in educational institutions and industry.

This paper has described some of the technical features of CD-I, in particular the audio and image data formats, and has outlined some of the processes involved in creating a CD-I title. Our enthusiasm for the technology is based on our first hand experience, together with visits to major centres of CD-I development in USA, UK, and Europe. When the technology is finally release in Australia, in September 1992, we anticipate strong corporate and educational interest in developing training materials, with products offering general education and information services.

Authors: Dr. Neil A. Shaw & Graham J. Standfield
Computer Aided Learning Centre, Victoria University of Technology

Please cite as: Shaw, N. A. and Standfield, G. J. (1992). Compact disc interactive (CD-I): A multimedia system of the future. In Promaco Conventions (Ed.), Proceedings of the International Interactive Multimedia Symposium, 409-414. Perth, Western Australia, 27-31 January. Promaco Conventions. http://www.aset.org.au/confs/iims/1992/shaw.html

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