In my Litchi missions, I find that the number of waypoints isn't terribly important, but rather the number of POIs and the abrupt changes between them is far more important, particularly if you are flying faster than 10 mph or so. When the POI focal point changes at a waypoint, you will be yawing the AC through a wide arc sometimes, even if the AC flight path is straight as an arrow. Swinging the AC from one POI to the next can cause a jarring pan in your video if they are 90 degrees apart. In contrast, the flight path can have very acute angles of even 180 degrees, yet they are hardly noticed at all in the video, if the POI focal point doesn't change before and after the course change.
So, if you want smooth video, pay much more attention to POIs, and when you plan to change focus between them, rather than the number of waypoints. Interpolation works well but keep in mind, if you add more waypoints, you actually get worse results, not better, because the machine has less time to change focal point between the waypoints. Interpolation is much smoother when the AC has a lot of time to work with and yaw happens more slowly between waypoints that are spread further apart, because the algorithm is trying to fully complete the required tilt and yaw before the next waypoint.
