Using masks as transitions...

[finchy]

Hey, im just trying to figure out how to create a transition like this (link below) in AE, ive been given a few rough tips bit i am just wondering if any body knows a good tutorial for it...?
thanks!
http://vimeo.com/179486

[tashbee]

this should do the job :)
http://blip.tv/file/get/Minormedia-TransitionTutorial336.mov

or its tip 7 on this page
http://forums.skateperception.com/index.php?showtopic=188919

theres also some other neat stuff with aftereffects there