Warning: excessive slow-mo alert. Three-and-a-half-minutes of mood music. The latest promo for Mercedes South Africa, “Silver Slipstreams,” is meant to highlight the sleek features of the A 45 AMG, but the clip really turns into a glossy skateboarding mixtape. Where’s Jon Hamm’s throaty lullaby voice when you need it? And shouldn’t the car be in the foreground, while the skateboard is in the background? This spot is beautifully filmed, the black-and-white adding interesting texture to the visual stunts, but it all drags on like a bad middle-school video project. Editing matters. Less is more. This would be better served as magazine art.