www.pudn.com > cdx.zip > README.1ST

 
 
19 April 1994 
 
 
	This package is a freeware source code kit for a CD Audio 
utility for DOS.  It uses low-level MSCDEX functions to do its job. 
I've been interested in writing a soup-to-nuts CD Audio Windows app for 
a while and find the Multimedia functions in Windows to be somwhat 
slow.  They're also limited in that they don't support access to all of 
the housekeeping info (and none of the raw audio data) stored on a 
Redbook (audio) CD.  One of the things I was interested in accessing 
was the UPC string audio CDs are *supposed* to possess, so that I'd 
have a completely unique ID for all audio CDs encountered by my 
program.  It turns out that UPCs aren't normally found on audio CDs, 
but in porting this code to work under Windows I learned a lot of other 
interesting stuf, but that's another story.... 
 
	Anyway, CDX (the principal program contained in the kit) is a 
nice little command-line util for controlling an audio CD from DOS. 
The version of CDX contained in this archive was created using Borland 
C++ 3.1, altho with a few minor changes it would work just as well with 
MS C++.  In fact, the 1st cut of my Windows port has been compiled w/ 
VC++ 1.0 and works very well.  The program, as supplied, compiles 
cleanly and generates no warnings or errors of any kind. 
 
	This is a real C++ program, altho it didn't have to go that 
way, because I don't think that "objectifying" the interface has really 
added to the clarity of the code and the services it provides.  I 
picked up the original sources from the BBS ether, but it was a 
non-working pile of junk.  After a week or so of steady work, I was 
able to not only get this to compile but I also understood how CD audio 
programming works and was able to flesh out a C++ framework that seems 
to make some kind of sense.  However, one should be aware that this is 
still a work-in-progress and there are a few aspects of the project 
that haven't been fully implemented or (for that matter) completely 
thought out, since I stopped working on the DOS version.  Case in 
point: I noticed, when testing the program on a self-loading, dbl-speed 
Mitsumi drive, that the program should wait a few seconds for the drive 
to become ready after loading a disk, so that the TOC can be read on a 
single pass. 
 
	The theory of operations is simple.  The main program module is 
CDX.CPP.  Its main() fn initializes the CDRom class, then instantiates 
a CDRom object and issues hi-level commands to that object, 
corresponding to the types of things a user would want to do w/ an 
audio CD.  The main pgm also displays the CD's TOC (Table of Contents) 
and the status of the current audio program in progress.  The CDRom 
class translates these hi-level commands into MSCDEX commands via the 
IOCTL class.  The driver program only performs a single hi-level 
command at a time, but that was all that was needed to get the project 
started.  There is also a trivial program included (CDS.EXE) that shows 
a minimal use of the classes, which I used to check out a couple of 
routines (that didn't fit into CDX) and certain MSCDEX status 
operations. 
 
	The code has loads of comments, so there should be no ambiguity 
about how things work.  I haven't done anything to support multiple CD 
drives on a system, altho that aspect of the code can be fleshed out w/ 
in an hour or two.  I've also subsequently discovered that the 
CDRom::PlayPreview() fn isn't well implemented because it samples the 
Q-Channel for the end of the audio span and can result in some weird 
results that may cause the sampling loop to fail.  (The 1st Windows 
port simply lets each preview span terminate before commencing to the 
next track to preview.)  I had to change the memory management scheme 
for the Windows port and struggled with this for quite a while, hence 
there is no longer a single source for all versions of the code.  One 
minor improvement implemented for the Windows port is that the IOCTL 
class now uses the DOS multiplex interrupt to talk to the driver 
instead of directly calling the CD-ROM device driver 
strategy/interrupt routines. 
 
	Finally, this code is committed to the public domain, so do 
with it as you will, as long it's understood that I take absolutely no 
responsibility for anything that may happen as a result of using any 
code or programs in this kit.  CDX has been tested on three different 
CD-ROM subsystems and works well w/ all of them.  Hope you have fun w/ 
it.... 
 
 
Jethro Wright, III 
Hempstead, NY