oh my goodness! he is DELICIOUS!
but that service motion...
he is, like, UNDER the ball falling backward. Guille, you toss the ball in FRONT of you so you can lean INTO the shot, thereby generating power from the rest of your body. This also helps in PLACEMENT of your serve, so you can begin the point in an advantageous position for the rally.
You will need to work on that... you're going to give yourself a lower-leg injury with this compacted body configuration.
I mean, yeah you're supposed to have a deep knee bend, but that's....not what that is you're doing.