They used footage of May Productions Hollywood Night 1 when Ngoc Lan performed this. During the chorus, Lam Thuy Van sang harmony on top of Ngoc Lan’s melody. Very nice. But LTV is layed there the whole time. Yes, layed. She just layed in the middle of the stage the whole time and sang. In a black dress i believe.
According to Nam Loc, Asia and May Productions are currently working on a DVD about the life of Ngoc Lan to be released in the near future.