[Openal] How to capture Listener output?

[Chris Robinson]

On Wednesday 12 March 2008 12:36:56 pm Brad Aisa wrote:
> I want to use OpenAL in a robotics simulation context. What I
> want to do, is capture the audio stream of the Listener, for
> input into my robot's auditory processing subsystem.
>
> How can I do this?

Hi Brad.

It should be possible as long as you can configure your audio card to capture 
its own output. Under Windows' mixer settings, it's likely a "Stereo Mix" 
capture option. Then you can open a sound device for OpenAL output, and open 
a device for OpenAL capture, and the capture would get the listener's output. 
You would need to be careful because it would also capture other system 
sounds, however.

Depending on your OS and implementation though, there may be other ways to do 
it, too. Under Linux with ALSA, you can redirect the 'default' device to 
write to a fifo (using ~/.asoundrc), then have your app watch and read that 
fifo. Additionally, using OpenAL Soft in Unix-like systems, you can configure 
the wave file writer to write to a fifo and do the same thing, without the 
need for a sound card.

But do note, regardless of the available methods, OpenAL processes 
asynchronously. It would be constantly processing data in the background in 
real time as you updated the listener and sources, without a way to tell it 
to processes a specific amount at a specific time. If it's outputting to a 
fifo, processing will block as long as you're not reading from it, but this 
isn't terribly exact.