Camera path contraints I am creating a path for the camera in a scene. I need the camera to follow a NurbsPath, and then half way through the path, it needs to track a certain standing object. In order to do that, I am using two different camera constrains. One is "follow track" that applies for the entire clip. The other one, is  "Track to” which take place in the later part of the clip. The problem is I can’t figure a way to do that smoothly. So far… I created two different clips (one with one constrain and the other with both) then created a third track between the camera position between the two. However, the results were not smooth and the camera swerved a lot in the middle clip 
I wonder if you can come up with a better way of doing this.
Make sure the Track To constraint is below the Follow Path, this way if you enabled Follow curve in the Follow Path constraint, the Track To will override it, and you will be able to animate its influence: