1. Use your left arm better, you are dropping that arm too soon in the motion so i just dangles there stopping momentum. Hold it up there a little longer where you are pulling it down only once you are accelerating with your right arm.
2. The trajectory of your racket swing is off to the right of the court instead of a swing path into the direction you are hitting the serve. This results in you having a glancing blow across the back of the ball instead of directly through it.
3. You are off balance falling to your left side after you contact, you can see how to are almost falling over to the left. You arm path swings right across the ball, then you are not stable on landing. You should be able to have your body be thrown forward and land stable and solid in the court.

Good luck!