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.