Snipping Tool (Windows 7) capture from frame in your video.
you are contacting the ball....(?).... with that angle in your elbow you are not doing what high level servers are doing. Their arms are about straight at impact. There is
an angle between the forearm and racket.
It addition, - I don't know this but suspect - accelerating the racket with a bent elbow could be stressing your arm in some way that might cause Golfer's Elbow injury. ??
Examine the arms and forearm-racket angles for high level servers at impact.