I took a stab at it:
Code:
alias totmp3 {
  var %drive = $?="Drive letter like C: "
  window @Mp3 10 100 200 75
  aline @mp3 Start
  echo -s $finddir(%drive,*.*,0,totmp3-2 $1-)
}
alias totmp3-2 {
  .echo -q $findfile($1-,*.mp3,0,totmp3-add $file($1-).size )
}
alias totmp3-add {
  set %totmp3-raw $calc(%totmp3-raw + $1)
  totmp3-display
}
alias totmp3-display {
  window @Mp3 10 100 200 75
  rline @mp3 1 $bytes(%totmp3-raw,g).suf
}


might be a starting point anyway