This is a contender for my favorite video I've ever shot. The light was perfect and the angle is fascinating.
Technique-wise watch how as Andy rotates his shoulders, the arm really supinates. The wrist lays back and the forearm rotates upward. This gets his racket "in the slot" with his shoulders squared up to the net.
He continues to rotate his shoulders and lift the double bend to the ball (watch his elbow slide in front of his body for visual proof). On contact we see an enormous push/lift of the ball. Several frames later his upper arm is parallel with the ground and the elbow is extended way forward from his body. When the upper arm is parallel to the ground and the elbow is well in front of the body it is absolute proof that the player has lifted the ball and really pushed through it in a powerful way.