I originally wrote this library back in roughly 2002 to workaround bugs and limitations I was facing with SDL_mixer. I was experiencing latency problems back then with SDL_mixer on certain platforms and I needed the ability to play both music and speech simultaneously which the design of SDL_mixer does not really facilitate. I also needed more decoding formats than SDL_mixer supported, plus at the time, the SDL_mixer backend for music used a different decoding backend than the rest of the library which made it inconsistent.
The ALmixer code was written very quickly in a matter of several weeks. But in solving all the problems/limitations I had with SDL_mixer, I encountered a whole set of new problems surrounding OpenAL. Back in 2002, OpenAL was on life-support and the 1.0 OpenAL spec was really broken. The differences between implementations of OpenAL differed greatly which made it very difficult to ship a cross-platform application using OpenAL.
Meanwhile, because the code was written so quickly and also happened to be my first venture into audio (among other things), I felt the code was messy and needed to be cleaned up. The complicated state machine necessary to do what I needed turned out to be very scary. In addition, with all the hacks I needed to add to workaround OpenAL implementation differences, made the code much more complicated.
So rather than releasing to the public, I decided to sit on the code and vowed to clean it up some day so I don't embarrass myself. I also expected that SDL_mixer would be rewritten to use SDL_sound soon and maybe some of my other issues might finally be fixed.
Many years passed.
OpenAL 1.1 was ratified and many of the compatibility issues between OpenAL implementations started going away. Every so often, I re-pickup ALmixer and made small changes to update it to support OpenAL 1.1.
Fast forward to 2010 (today). I still haven't cleaned up ALmixer. SDL_mixer has still not been rewritten. And there haven't been any great audio libraries that have emerged in all these years. Furthermore, with renewed interest in playing high performance audio with OpenAL due to the enormous success of iPhone, iPod touch, and iPad, I see there is a still a great void that needs to be filled. (In fact, I just co-authored possibly the most comprehensive book on OpenAL ever written: http://playcontrol.net/iphonegamebook)
And I have recently been working on a project that would benefit greatly from something like ALmixer. I realized that I don't have the time/money to do the clean-up, nor is it feasible for me to do an entire rewrite. I also realize that despite the scariness of the code, the library seems to generally work.
So I have decided to finally release ALmixer, even without the clean ups. My hope is people find it useful and I also get some good testing feedback. Maybe some heros will even make it better. Please be kind when reading the code and reporting bugs. I admit the code is scary and many of the comments are now obsolete.