Speed Graph In Graph Editor? I have a camera moving along a path. The camera position is controlled by an animated Offset value in the Follow Path modifier. 

By setting keyframes for the Offset in Graph Editor I can change the camera offset in different sections of the curve, but what I really would like to do is control its speed (the first derivative of the offset). Is it possible to add a speed graph in the Graph Editor?
The animation speed is a property of the path, called "Evaluation time". You can find it in the curve's properties. When you animate the path in the constrait menu Blender creates a curve modifier for it in the graph editor. After you delete it you can animate the property as any others, or you can also modify the generator modifier.