Footprint or breadcrumb animation I'm after a very specific effect and I haven't found an effective way to accomplish it.  Basically, I want dots to appear along a path and disappear over time.  The dots should not move after they're born, only fade out via alpha channel.  It's important that this is an actual alpha transformation, not just a color blend, because I plan to overlay this graphic on different source videos.  The paths also need to be easily editable and there will be hundreds of dots, so individual layers for each dot is out of the question.  

The best way I can describe the effect I'm after is: Imagine a person walking through the snow, the footprints appear instantly, and fade out over time.  I've seen plenty of tutorials on creating a series of elements which follow each other, as if you're dragging a string of pearls, but this is not what I'm after.

I've tried After Effects, and it's easy enough to make a dotted line with a shape layer, but a gradient stroke doesn't follow the path, or give me control over start position, end position, or offset.  (here's an illustration of the problem)



I've also tried using Cinema 4D and mograph, but keep running into similar problems.  I basically can't get a graduated shader effector to follow a spline.  

Any solutions which use C4D or AE are preferred.  All are welcome.  Thanks.
A simple way in blender or any other 3d package would be to use a boolean modifier, if you want to subtract real geometry:




use a array modifier to duplicate your shape
create a path and aligning the objects on it
animate the object count of the array modifier
create a simple geometry for subtracting the path objects at the beginning
add a boolean modifier to your base object
animate the position of the boolean object to subtract the shape objects
make the boolean object invisible to the camera (e.g. with a transparent material)




.blend file



Edit: To get a soft transition you can render the bool object seperatly, blur the alpha channel and subract it from the another alpha. Or simply use a roto mask. 





.blend