[Openal] Openal, S/PDIF and surround

[Alfredo Pironti]

Hi list,
I'm writing here for some support, because I searched and experimented a 
lot, but I was unable to make my openal configuration work.

On my computer, I only use S/PDIF for output. When I listen to music, 
the stereo data are sent through S/PDIF, and everything is OK. When I 
watch a DVD, then the AC3 passthrough on S/PDIF works with no problem, 
and my receiver decodes it correctly.

And now with openal. Openal is sending stereo data through S/PDIF 
perfectly. However, I would like it to send AC3 data (or any other sort 
of surround data) over S/PDIF, so that I could enjoy my games 
(tremulous, for instance) with full surround effect. Searching around, I 
found only configurations using the "surround40" or "surround51" 
interfaces, which I think is not my case. I also tried to specify 
"spdif", "spdif:0", "hw:0,1" (the digital playback) as interfaces, and 
4,5,6 as channel numbers. However, I could never get surround sound, 
only stereo data were sent over S/PDIF.

Where am I wrong? Is it possible to obtain what I'm looking for? In the 
case openal is not able to generate AC3 directly, is it possible to let 
openal generate the 6 channels audio, and then encode them in AC3 via 
software, and send them via S/PDIF?

Thank you very much for your support! If we find a solution to this, I 
may write down a short document/tutorial, so that other people can enjoy.

Cheers,
Alfredo