The CD-i format is developed as a full standard, just like the audio compact disc. Everything this standard needs to conform to is described in the so-called "Green Book", developed by Philips and Sony. The first version of the Green Book was released in the late eighties. It was updated and clarified several times and significantly extended once by the addition of the Full Motion Extension for MPEG audio/video playback, resulting in the final May 1994 version.
It is mainly interesting for CD-i developers who need to know the ins and outs of the CD-i infrastructure. But also in view of historical value it's certainly worth a look. As cdifan describes it: "It is important for a CD-i developer to have a basic understanding of the available audio and video data formats and the available CD-RTOS system services, but completely reading and comprehending the Green Book is usually not required."
The Green Book was originally not freely available and had to be licensed from Philips under non-disclosure agreements, but since at least 2011 the May 1994 version is available here:
https://www.lscdweb.com/data/downloadables/2/8/cdi_may94_r2.pdf
This version of the Green Book and several related documents are also available from the CD-i 'Documentation' section of the ICDIA website at http://icdia.co.uk. As I recently got some questions about where to get more info about it, that's the time we put in on the frontpage of Interactive Dreams. The May 1994 version of the Green Book contains the following sections:
TOC Table of Contents
Chapter I Introduction
Chapter II CD-I Disc Format
Chapter III Data Retrieval Structure
Chapter IV Audio Data Representation
Chapter V Video Real Time Data Representation
Chapter VI Program Related Data Representation
Chapter VII Compact Disc Real Time Operating System
Chapter VIII Base Case System
Chapter IX Full Motion Extension
Appendix I Glossary of Terms
Appendix II CD-I Disc Format/Subheader Values
Appendix V Video Real Time Data Representation
V.1 CCIR Level Assignment
V.2 Guidelines for 525/625 Image Interchange
Appendix VII Compact Disc Real Time Operating System
VII.1 CD-RTOS Technical Manual
VII.2 CD-I Peripherals
These chapters and appendices specify the low-level interfaces available to CD-i titles, including all the nitty-gritty details of the CD-i disc format and the system-provided services (system calls). The CD-i specific system calls are specified in Chapter VII using their 68000 machine language bindings; the standard OS-9 system calls are specified in the referenced OS-9 Technical Manual.
cdifan goes further into the contents: "Chapters I to VII specify the functionality of a CD-i player including a number of possible extensions of the basic functionality (e.g., additional video modes or resolutions). Chapter VIII specifies the so-called Base Case System which has the minimum functionality required for all CD-i players. It specifies a 16-bit data bus version of a 68000 family microprocessor with two RAM banks of minimum 512KB each and an X-Y pointing device as the only guaranteed human input device.
Although a keyboard API is specified in the Green Book, no Base Case CD-i player is required to have a keyboard; in fact CD-i keyboard peripherals were not widely available for consumer players until the introduction of the CD-i KeyControl in 1996. Chapter IX specifies the Full Motion Extension of the Base Case System; the MPEG data formats and system services described in this chapter are not available on all CD-i players. Most of the Philips players could be upgraded to the extended version by inserting a Digital Video Cartridge or DVC which was usually sold separately (some player models have it built-in). In released CD-i players, the Full Motion Extension is normally accompanied by a 1MB memory extension as specified by a player implementation recommendation that is available from the CD-i DOCUMENTATION section of the ICDIA website at http://icdia.co.uk. Note that no current software CD-i player fully supports the Full Motion Extension. There are various reasons for this, including MPEG patent restrictions and development complexity. The original paper Green Book comes in a thick three-ring dark green binder on 6” x 8” paper.
At SPC Vision we worked for many years with bound A4 copies of the October 1992 version and a ringbound A4 copy of the March 1993 version of Chapter IX, both of which differ in only minor details from the final May 1994 version of the Green Book. Later we acquired two “original” Green Book binders containing the September 1990 version, but we never used those during development."
More valuable information about developing on CD-i, read it here:
https://www.theworldofcdi.com/wp-content/uploads/2019/03/CDiDevelopment20190331.pdf
[Thanks, cdifan, CD-i Development in the 21st Century]