Portaudio:
Start by going here:
http://www.portaudio.com/
Portaudio is a C library, but it's easily wrapped in C++.
The basic procedure is like this:
1. Initialize the library.
2. Pick a sound device (or go with the default)
3. Write your callback function. Your callback function should take sound data from your own internal structures and copy them to POrtAudio's buffer. PortAudio will call your callback function at regular intervals.
4. Start PortAudio when you're ready to start processing sound.
5. Read some number of samples (usually done in a different thread, and most importantly, POrtAudio doesn't read any sound files, you need a separate reading library)
6. Mix the samples or process them (do this internally with your own code)
7. Place the samples in your own buffer
8. GO back to 5, repeat until done
9. Stop the player
10. Destroy everything, leave no memory leaks, etc.
It's a fairly straightforward API. You should read the portaudio.h file and then come back and talk some more.
For reading the sound files, you'll want to try to get SDL to read them as much as possible. If you want to read a mod file and render it before sending it to portaudio, you'll have to get a mod reader (or write one, I can dig up my post on the Hydrogen list that has a link to where mod files are described in detail for programmers). When all else fails, libsndfile is your friend.
Audacity uses libsndfile and portaudio. THeir import functions use other libraries as needed, such as lame or libvorbis, or whatever. But the base program uses libsndfile and portaudio.
Generally you link portaudio directly into your application. So you don't link to it as a shared library, and you don't have to worry about dll hell with it. It's a small enough library that this is the *best* way to handle it. It compiles out of the box on gcc on any number of platforms, and pretty much every compiler microsoft has on the market right now.
On Ogg Vorbis:
I think aa should support a number of formats, but the default installation should be small. So it should support ogg and wav and mp3 and all sorts of stuff, but it should only come with mod because mod files are so small. That would make for the best soundtrack possible for a small download, and still give us 3rd-party people a way to make really nice soundtracks, but the price of the really nice soundtracks of course is the size of the download.
