Originally Posted by Chas Tennis
4) Take some videos from the side. Probably perpendicular to the ball's trajectory might be better than along the baseline.
If you do this, I believe one thing you will notice is your ball toss. Judging from where you start and where you land, I'd guess your toss is either straight-up or worse, behind you. Ideally, if you toss the ball but don't hit it, the ball should land ~ 1-2ft inside
Two other things to note:
1 - While you got better as the serves went on, you should try to get a full arm extension at contact point. The first couple your arm was still bent when you made contact w/ the ball.
2 - Try to keep that left hand up a little longer. It will help w/ balance, as well as power.
3 - The abbreviated, straight-up takeback motion is good, but you may want to sync it up w/ the ball toss. You're bringing the racquet up, then starting the toss.
A good reference for all 3 of the above suggestions is Patrick Rafter's serve: