Using Masks to create chases on separate slices with different layers

[crazyhotpockets]

Hello! (:

I am preparing for a festival that I am going to running visuals for in September. The stage design I just got today and it features ALOT of LED tile squares about 46. I have everything mapped out here at home and working wonderfully except for one thing. I created a Mask chase in After effects and I cannot get it to properly work. I have the tile slices routed to layer one, then I copied all the slices in the exact position then routed those slices to layer two. using Mask50 When I turn both layers up. I only get the white chase that I made and it doesn't properly mask the layer beneath it. I am thinking this is because it is on two separate Slice groups. I am wanting to know what the best way to achieve this look would be. Or what I am doing wrong. Thanks for any and all help!

[Zoltán]

you have to use composition as slice input if you want to be able to mask with video - layer compositing works only this way.
so for example
layer 1: content video
layer 2: other content video
layer 3: masking video

if your masking video is black+alpha - leaving whet you want to see transparent, then layer set to alpha 100% opacity,
if its white where you want to see your content then layer 3 set to multiply, 50% opacity. (or mask50 at 100% opacity)

also you'll need only one group of slices this way.

[Joris]

I'm just going to leave this here...

http://chaser.hybridvisuals.nl/