Converting track keyframes to bezier curve

I am looking for a way to convert the data from a video 2D track to a bezier object where the natural changes in speed of the filmed object are translated to the bezier.
An example would be, someone painting with light. You film someone with a torch, track the torch and use the track data to create an object that “grows” as the pointer moves.
I have tried using the grease pencil and the bezier tool to create the object but animating the bezier’s reveal is more tedious than I thought.
I am sure there is something very simple … I just can’t find it.
Any ideas are very welcome

i would personally not use blender for 2D tracking, i think they got tools for it, but ive never looked for it. i would make the glow stay in one position, and just play with rotation, rendering as a PNG sequence, and use aftereffects to track and place the glow to whatever you want it to follow.