After Effects - Mask with rotobrush

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Hello everyone, 

I am very new in AE. I am having difficulty with rotobrush and masking. 

I have 2 videos:
1. a man walking: I used this one with rotobrush in order to have the walking silhouette. 
2. an "abstract" video: I want to use the walking man "cut-out" (using rotobrush) as a mask to this one. So I would be seeing an abstract video with  the shape of the walking man. 

It may sound very basic but I couldn't find on YouTube either. Maybe I am using writing keywords. 

Thank you 

[Hariraman23 · Accepted solution]

Hey ,

Please check this tutorial.
https://www.youtube.com/watch?v=Inva9Xf3gQ4

Hope it would be usefull.