from Garner's Usage Tip of the Day
The traditional American English preference, both in this phrase and in "short-lived," has been to pronounce the second syllable /lIvd/, not /livd/. (The sense is "having a long life," and the past-participial form has been made from "life" [/lIf/], not the ordinary verb "live" [/liv/].)
But the predominant practice today -- and the British English preference -- is /livd/. The American tendency to make it a short "-i-" is perhaps explainable on the analogy of the ordinary word "lived"; the British tendency may be influenced additionally by the phrase "long live the Queen."