A Replicator is the way to go to start. Draw a bezier line in the path you want the footsteps to go, then uncheck its visibility checkbox so you can't see it. Create a Replicator of your footprint. Change Shape to Geometry, drag-and-drop the bezier line into the Shape Source box. Set the number of points for the number of total footprints you want to end up with. Check off Align Angle and change Angle to 90 degrees.
Now, I'd take and draw a shape and animate (keyframe) that shape to act as a mask and reveal the footprints one by one as needed.
That's the quick and dirty way to do it. But this does inspire me for a new macProVideo.com tutorial on how to do this in Motion. There are some more advanced options that could make it cleaner.
Thanks again for the advice. Alas it won't work for my project. I'm projecting onto a large building and what I want is footsteps walking on the walls, avoiding the windows. So the footprints need to follow a motion path. I've tried using a replicator but getting the shoe to be visible, then turn off and move, and for this to alternate from left to right, hasn't happened. Once I've cracked it I'd use different styles if print to create multiple patterns.
I'm sure it's the replicator I need, probably combined with a behaviour, or even an emitter.
"So the footprints need to follow a motion path."
I told you how that is done by using Geometry for the Shape parameter.
You'll have to do tests on that building live to figure out the correct placement of your foot steps.
It's clearly something easy to say but not do! I've mapped the building and have no problem with that end of the project. But Replicators will, well replicate. I want the boot print to come on, pause for a few frames, go off and reappear further along. I've used motion for years but judging by your tone I'm missing something very obvious? Thanks anyway.