Getting the final sound buffer from the sound card

[jizbqMoL]

I am trying to build a game that takes input in the form of all the audio the player is currently playing. So in theory the user could open and play a sound file, plug in a mic, etc. and the game would be able to react to all of it. However, I'm not sure where to start. If anyone knows of an audio library that would provide that kind of functionality, or have any other advice, I'd really appreciate it.