Marketing Video from Audio & Demo

Freelancer.com creative contest — guaranteed prize of $25 USD. I already have two key assets on hand—a clean, studio-quality audio clip and a rough demo video that shows the product in action. What I need now is a single, cohesive marketing video that marries the soundtrack with engaging visuals, on-screen text, and light graphics so viewers quickly understand what the product does and why it matters. The audio comes first: Add some visuals to the Audio. Then splice the Video at the end of it. The finished piece should feel informative rather than sales-y; every shot, lower-third, and transiti