How to add and animate infinite strokes in After effects

[Arvin35988473256j]

Hello!

How can I recreate this animated infinite strokes scene from Ariana Grande - Problem ft. Iggy Azalea.
I plan to mask the subjects in my video using rotoscope but I don't know how to replicate this infinite strokes effect. All suggestions are very much appreciated 🙂 

[Mylenium]

The Radio Waves effect is your friend.

Mylenium

[Arvin35988473256j]

Hi! I tried adding the radio waves effect on a keylighted clip but the generated echoes were only circle and not coming frmo the shape of the masked object. What step/s did I miss? Thank you for your help 🙂 

[Mylenium]

Set the mode to image contour.

Mylenium