In modern (June 2007) Debian Sid, multiple simultaneous audio streams are supported ‘out of the box’ using the ‘dmix plugin’, whatever that is. You do not have to configure it. The only problem is, it does not work with mplayer audio streams.
I found the solution through the Alsa Wiki. To get sound in mplayer and to hear sounds (such as the Skype ringtone) from other sound-producing programs at the same time:
- Put in ~/.bash_profile:
export SDL_AUDIODRIVER=alsa export AUDIODEV=plug:dmix
- Put in ~/.mplayer/config:
You don’t need an ~/.asoundrc or an /etc/alsa.conf file. You also do not need to set up jack, artsd, or esd (although you cannot remove the packages from your system, because of, probably mistaken, Debian dependencies).
I do not know if this solution (or indeed this problem) is the same in other Linux distributions, including other versions of Debian.