sox -v 0.95 InputFileName.wav -e u-law -r 8000 OutputFileName.wav
-v volume
-e encoding
-r sample rate
Fonte: http://www.888voip.com/forum/yealink/600-creating-wav-files-for-yealink-ringtones.html
sox -v 0.95 InputFileName.wav -e u-law -r 8000 OutputFileName.wav
$> mplayer -dumpaudio video.avi -dumpfile audio.mp3