# record from PulseAudio device 11
open my $voice, 'ffmpeg -hide_banner -loglevel error -nostats -f pulse -i 11 -t 30 -ac 1 -ar 44100 -f s16le - |';
binmode $voice, ':raw';

while( ! eof($voice)) {
    read($voice, my $buf, 3200);
...