What did chief justice burger say about executive privilege? how does that justify his decision about nixon releasing the tapes?

Chief Justice Burger, in the Supreme Court case Nixon vs United States, he ruled that executive privilege is not determined by the president. Rather, it is up to the courts to decide. In this case, Burger states that the presidents attempt to hold the tapes was unconstitutional.

He uses this reasoning to force Nixon to release tapes of his conversations from the Oval Office.