interpolating to a non fixed position

is there an equation or formula which can make object interpolate to a moving object in a given time.

the second object movement isn't linear nor can be calculated.

the first object's movement doesn't have to be smooth.

example: camera is above an object - like geometry wars - and let just say there two analog stick one to move the player on the 2d plane, the other one is to move the camera a little pit from the player and when you let go of it it interpolates to the player even though the player isn't moving linearly.

real game example-{salt and sanctuary}