Track mattes

- [Instructor] While a mask allows you to control…what's shown or hidden on a particular layer,…After Effects also allows you to reference…another layer's transparency or pixel brightness…to control what is visible.…A layer that controls another layer's visibility…in this way is called a track matte,…and here in this movie, we'll explore how they work.…So in this first example, I have some numbers…that I have going up in space and Y,…and basically I want to create a counter of sorts.…Now, you'd think that maybe with our masking tools,…I might be able to cut out a certain portion…and have the rest of it kind of revealed,…so let's go ahead and select our layer one,…and come over here to our rectangle tool,…and just draw a little mask around that layer,…and when we preview it, you'll notice…that the mask is moving along with the layer,…not what I intended, I actually wanted…to keep my mask in place and just move the layers,…so that's kind of an important concept,…is that these masks are moving along…with whatever the layer is doing, so if I rotated it,…