A fully extended tossing arm will make your toss a bit more consistent.
You do decently well to keep your tossing arm up and really use your shoulders to generate speed, but if you'll go to about half-way through the video and go frame-by-frame you'll notice a few things, the first of which is something you can easily improve to effortlessly create more racquet head speed:
Compare these two:
Safin, in this second serve, has completely brought his feet together but his arm is still pointing up at the ball. You, however, have already started dropping your arm by the time you've brought your feet together and are starting to unwind. By the time you make contact with the ball, this dropping of your arm and early unwinding has caused you to lose a lot of power that you could have otherwise put in your shot.
My suggestion: make a conscience effort to keep that arm fully extended and pointing at the ball until you start your upward leg thrust. Then, as you're moving upward towards the ball, bring your right arm down and left arm up (like a pendulum) and you'll notice how much more power is translated as a result, and how effortlessly you'll be able to turn this racquet head speed into extra spin or speed (or both) in your serve.
If you feel as though you don't have enough time to go through this motion, which will probably happen because your toss looks relatively low, then try throwing it a bit higher. Even if it causes you to started hitting the ball as it falls, the extra time will allow you to setup and also the downward motion of the ball will automatically cause even more topspin to be added onto the ball due to an effect called shearing. Just my two cents though, give it a shot and see if it helps you a little
