The libspotify documentation for the Track subsystem makes no mention of metadata. You can see that extra metadata (such as ISRC) is present by using the XML Metadata API:
http://ws.spotify.com/lookup/1/?uri=spotify:album:6G9fHYDCoyEErUkHrFYfs4&extras=trackdetail
<album><name>Remedy</name><artist href="spotify:artist:4YrKBkKSVeqDamzBPWVnSJ"><name>Basement Jaxx</name></artist><released>1999</released><id type="upc">634904012922</id><tracks><track href="spotify:track:3zBhJBEbDD4a4SO1EaEiBP"><name>Rendez-vu</name><artist href="spotify:artist:4YrKBkKSVeqDamzBPWVnSJ"><name>Basement Jaxx</name></artist><available>true</available><id type="isrc">GBBKS9900090</id><disc-number>1</disc-number><track-number>1</track-number><length>346.158000</length><popularity>0.37000</popularity></track>[...etc...]
Here the album has a UPC code and each track has ISRC. Will this ever be available through libspotify or does it need a second query using the XML Metadata API once I've got album/track links from the API?
