Few live performances in pop history carry the weight of this one. Whitney Houston and Mariah Carey took the stage at the 1999 Academy Awards to perform “When You Believe,” the duet from the DreamWorks animated film ‘The Prince of Egypt,’ and the result is exactly what happens when two of the greatest voices of their generation share a microphone at the peak of their powers. The high-quality footage, now circulating widely on YouTube, serves as a vivid reminder of just how commanding both artists were in that moment, two voices pushing each other higher in front of one of the biggest audiences in television.