[alsa-devel] Capture and playabck together

Emmanuel Milou emmanuel.milou at savoirfairelinux.com
Wed Feb 20 17:09:25 CET 2008

Hi all,

I am developping an open-source C++ softphone based on Alsa. We used to 
use Portaudio but we recently decided to switch to Alsa. I am quite 
unexperimented in Alsa dev and I got some difficulties to make it work fine.

My capture and playback devices are plughw:0,0. I am using read/write 
transfers. When I disable the capture, playback works fine; when I 
disable the playback, capture works fine. The problems occurs when I 
used them together. If I set hardware parameters for both, the playback 
sound is awful and there is no capture, and finally core dumped. If I 
set hardware parameters for the playback stream only, the playback works 
fine, but no capture, I just get an echo with an input/ouput error.

Where do you think the problem comes from? Isn't it possible to set 
hardware configuration for playback and capture? Is there a hardware 
ring buffer for each stream ?

Thanks for your help


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