Circle of Life Instrumental Demo track from the Lion King Legacy Collection looped to 30 minutes (practically forever!). This is the demo track that made the animators at Disney step up their game.

Fun Fact: The lullaby theme (looped here) from the Circle of Life is the same theme "Mother Africa" from Power of One (1992), another Zimmer score he made 2 years earlier, that got him the gig for Lion King and where he met most of the musical talent he used in Lion King, including Lebo M.