Chapter I  Introduction


I.1  Scope

A CD-I System is a real-time system capable of playing CD-I discs.    Such 
a system must  be capable  of decoding the  various types  of data   (i.e. 
audio, video,  program  related data)  at  the rate  at  which  they   are 
delivered from the CD-I disc.  As such the format of a CD-I disc must   be 
specified.

The first goal of this document is to  define explicitly the CD-I    MEDIA 
SPECIFICATION, which:

- specifies the physical format of a CD-I disc;

- specifies how  various information  types---audio data, video  data,   and 
                                                    program-related 
                                                    data---are coded  on  a 
                                                    CD-I disc;

- specifies how the various information types are organized on a CD-I disc; and

- gives guidelines about the data integrity and   tolerances required to use the 
                                                         CD-I medium.

This specification must  comply with  the specifications defined  in   the 
CD-Digital Audio (CD-DA) System Specification.  Furthermore, it is   based 
on the principle that:

- the CD-I information carrier is of a  fixed bandwidth as defined by    the 
                                                    CD-DA specification;

- the  CD-I information  carrier can  be substituted  for  a CD-DA   information 
                                                         carrier on any  optical 
                                                         medium; and

- CD-DA tracks, defined  in the CD-DA                specification,   may 
                                              be used on CD-I discs.


The second goal  of this  specification is to  assure that  all CD-I   and 
CD-DA discs  can  play  on  all  CD-I players  and,  in  particular,    in 
real-time.   As   such,   this   specification   details   the     minimum 
characteristics of a system that may bear the CD-I name.  This system   is 
called the Base Case system.

The third goal  is to  assure the extendability  of CD-I  systems in    an 
application recognizable manner.  In  the light of this  a   configuration 
status descriptor made up of peripheral status descriptors  is   available 
to the application so that it can decide the level of functionality   that 
may be offered to the user.

I.2  Structure of the Specification


Chapters II  to VI  are principally  CD-I media  specification   chapters. 
Chapters II, IV, and V are structured so as to contain:

- an encoding model;

      - a decoding model; and

      - the coding on disc

for the physical  formats, audio  data representations, and  visual   data 
representations respectively.

Chapter III gives the specification of the data  retrieval structure   for 
files while Chapter VI gives a specification of the program-related   data 
representations.  Based on a programming model, Chapter VII specifies  the 
CD-RTOS interfaces.  This latter chapter defines the interfaces    through 
which an application can access CD-I resources.

Chapter VIII specifies the Base Case System.  In particular, chapter  VIII 
specifies all the functions that need to be  supported by the Base    Case 
System as well as the resources that need to be available.  However,   the 
detailing of  performance aspects  will be  done after  the    disc/system 
validation is completed.

Each of the aforementioned chapters clearly define which  coding   formats 
or modules go beyond the CD-I Base Case System capabilities. When   coding 
formats or  modules go  beyond Base  Case capabilities  this  is   clearly 
indicated between the relevant text by:


                     *******EXTENSION*******
                        .
                               .
           .
                              text
                        .
           .
           .
                     ***********************


The approach to compatibility is defined so that  all CD-I discs will   be 
playable on CD-I players.

The appendices (numbered to be consistent with the relevant chapter)   are 
mainly used for clarification.


I.3  Conventions


Unless otherwise indicated in this document the conventions  used are   as 
follows:

Bit ordering

In this specification, the graphical representation of all    multiple-bit 
quantities is such that the most significant bit is on the left and   the  
least significant bit is on the right.

Example for 8 bits:

    msb                  lsb
    _________________________
    _b7_b6_b5_b4_b3_b2_b1_b0_
    _________________________
    _________ 1 byte ________

Byte ordering

Quantities which require more  than 8 bits for  their representation   are 
held in more than one byte on disc. For all such quantities, the  ordering 
of bytes on disc (as seen at the  interface to the disc driver) is    such 
that the Most Significant Byte is first and the Least Significant Byte  is 
last.

Multiple-byte quantities  are  represented  graphically  such  that    the 
left-hand-most byte is most significant and the right-hand-most  byte   is 
least significant.


Example - 16 bit quantity:

          MSB                 LSB
___________________________________________
_b15_  etc.        _        etc.    _ b0_
___________________________________________
_______1st byte____________2nd byte_______


Multiple-byte quantities in memory are represented such that  the   memory 
address of successive bytes increases from left to right.




Strings

Strings are always given between double quotation marks "___".

Hex

All Hexadecimal values are preceeded by a $.

Binary

All binary values are preceeded by a %.

Reserved

All bits or bytes defined as reserved in  this document should be set   to 
zero. Bits fields may be indicated as reserved by the symbol _.
I.4  Recommended vs. Mandatory


All  specifications  given  in   this  document  are  Mandatory     unless 
specifically defined as Recommended.