If you want to use your arducopter to create nice smooth videos you usually need to fly it manually to get nice smooth turns (apart from using a decent gimbal). If you fly a mission in auto mode you will notice that as your arducopter reaches a waypoint it will suddenly turn to the next one, not ideal if you want a smooth, flowing video. However David Dewey has been working on making some improvements to the arducopter code that allows you to fly smooth continuous curves between waypoints for great autonomous aerial videos!
Each spline segment is a cubic polynomial curve defined in 3D space, with 1st and 2nd derivatives continuous wherever two segments meet at a waypoint. This gives a nice smooth transition between curve segments during flight. It also saves time and battery, since abrupt speed and direction changes are avoided.
This is apparently being included in a future arducopter release, but if you cant wait to test it out you can find the code over on github