Хозяйке на заметку (https://trac.ffmpeg.org/wiki/Capture/ALSA):
modprobe snd-aloop pcm_substreams=1
и
pcm.multi {
type route;
slave.pcm {
type multi;
slaves.a.pcm "plug:dmix";
slaves.b.pcm "loopin";
slaves.a.channels 2;
slaves.b.channels 2;
bindings.0.slave a;
bindings.0.channel 0;
bindings.1.slave a;
bindings.1.channel 1;
bindings.2.slave b;
bindings.2.channel 0;
bindings.3.slave b;
bindings.3.channel 1;
}
ttable.0.0 1;
ttable.1.1 1;
ttable.0.2 1;
ttable.1.3 1;
}
pcm.loopin {
type plug
slave.pcm "hw:Loopback,0,0"
}
pcm.loopout {
type plug
slave.pcm "hw:Loopback,1,0"
}
решит проблемы с записью звука из приложений.