You're falling off to the left.
Your racket is wandering down during the forward swing loop, so you get no preload on the wrist, losing lots of swingspeed. Racket should point upwards, then on the start of the forward swing, a RELAXED wrist allows the momentum of the rackethead to drop the racket.
Your swing, as is, is very slow.
Thrust up and forward on each and every serve.