fgoptionalbonussoundtracksbin is a non-essential, compressed file containing a game's music. It exists solely to give users the choice of whether or not to include extra media in their download.
Arthur was a digital archivist for a dead-link forum, a man who spent his nights hunting for the "0.1%" of data that remained unseeded. He found it on a defunct Russian mirror: a 4GB file labeled fgoptionalbonussoundtracks.bin fgoptionalbonussoundtracksbin