Reread the OP's first post.
4' from the baseline. Still need to know how high is the camera placed.
I"m 5'11". Serving second serves, just topspin, not the twists, most balls bounce around shoulder high to someone my height. Serves IN count, nothing else counts. Shoulder high should be just under 5'.
Same with first serves that are topspin, like the vids, but those go much faster, same bounce height.
From a 63 year old who claims "100" mph first flat serves. With Dunlops, in sub 60 degree air temps, 400' elevation.