find . -type f -iname "*.webm" -exec bash -c 'FILE="$1"; ffmpeg -i "${FILE}" -vn -ab 128k -ar 44100 -y "${FILE%.webm}.mp3";' _ '{}' \;
from
modprobe: FATAL: Module vboxdrv not found in directory
sudo aptitude install linux-headers-`uname -r`
sudo modprobe vboxdrv