Very clear, when we put it on full screen, Wish my comment's were as clear...
By stepping back with your front foot, you're giving up 10" of court each and every serve. No good. Instead, do the step FORWARDS with the backfoot, or keep both feet 18" apart.
Your swing is not bad. However, you don't tilt your torso upwards, so you swing flat in line with your target. Instead, a tennis swing has to go upwards, striking the ball with a flat or rising rackethead, to get the most height at the strikepoint and to get the ball down and in. so tilt your shoulders so left shoulder is high, right shoulder low, at the trophy position, and LOWER your hitting hand to allow a swing upwards.