It's a collection of songs put out by Lind Erebros. The songs are titled things like "Fingolfin", "Elven Warsong", "Maglor's Cry", etc - I use it as background music for writing a lot (because I am love with it. Also, I don't get distracted trying to sing along most of the time, unlike Monsters and Men).

Nirnaeth Arnoediad is one of their songs.