I want to capture all audio that is played to the user (all sounds together). Currently I'm working on Windows but it would be nice if the code was cross-platform (but not necessarily). Is it possible to do it with OpenAL? How? Code examples would be great.
Language: C++
The only way to do this I believe is to create a replacement audio device driver that receives all audio requests, and then forwards them to the original device driver. There are a number of existing applications that work in this way including Freecorder, MP3myMP3 Recorder, SoundTap and Wondershare to name but a few (Google "Streaming Audio Recorder").
As for cross-platform, I would say not a chance since it is OS driver model dependent.
Depending on what you have in your system, some (not all) sound cards offer a "Stereo Mix" feature, which can be used like any other recording device. This is basically exactly what you want, as it is literally a mix of all stereo sounds being played.
来源：https://stackoverflow.com/questions/4578697/capturing-audio-out