Actually quite an easy problem, but I seem to be unable to find any solution for it.
I want to move objects along curves while moving the camera on another curve pointing at the objects; for this, I'm using a "follow path" constraint (with another "track to" constraint for the camera for the rotation) while animating the offset. Obviously, the rotation, location and speed of the objects/camera don't match up perfectly right from the start, so I'd like to manipulate the curves they're moving along on the go, or work on segments, perfecting them, then extrude the curve and move on. However, the "follow path" constraint seems to only feature a sort of "0-100%" offset, so whenever I manipulate the curve, objects move along with it, basically making it impossible to work properly. Is there any possibility to make the "follow path" constraint use a sort of "distance" offset, where extruding the curve won't affect previous segments of the curve (making the object keep its position) - like, an actual constant offset? It would be really painful/impossible having to have a perfect curve first in order to then line up camera/objects.
I appreciate any advise on how to achieve this kind of "live-tweaking" offset function.