title: What audio format Spotify uses and how they transfer the files to mobile devices?
body: <p>this question is just out of pure curiosity. </p>
  
  <p>I noticed, that when I sync my phone with my Spotify playlists, music is transfered really fast, I haven`t benchmarked or something, but it just feels times faster than just downloading 20 or so mp3s. </p>
  
  <p>How they do it ? Is it some kind of special audio format ?
  Or maybe they compress the data somehow when transfering ?</p>