XML format for mp3 files
You may run into a problem if a track has more than one artist.

You'd have to enter the track for each artist again, or you'd have to only use the first artist, or you'd have to create a new "combined" artist.

Why not omit the artist→track hierarchy?

&lt;collection&gt;
  &lt;track&gt;
    &lt;title&gt;Thriller&lt;/title&gt;
    &lt;artist&gt;Michael Jackson&lt;/artist&gt;
  &lt;/track&gt;
  &lt;track&gt;
    &lt;title&gt;Hey Jude&lt;/title&gt;
    &lt;artist&gt;The Beatles&lt;/artist&gt;
  &lt;/track&gt;
&lt;/collection&gt; 


Benefits:


You can add more metadata for tracks (composer, album, etc.)
You can add tracks without title and/or artist


If different artists may have the same name, you'd need a way to differentiate the artist elements; e.g. by using id with an ID of an artist database.