How to make a mask transition? (video attached for reference).

Hello,

Ive been trying to animate a mask such that it transists onto the screen but mostly all tuts on the web focus on animating the shape overtime.

Basically i want to do exactly on video 1.mp4 and somewhat in 2.mp4.

I asked the guy who did this and he said that he masked it in sony vegas.

I beleive both the effects can be done by a same way.

So if anyone can point me in the right direction will be very helpful.

Thanks.

Direct link to both videos only 1.28mb:

1.mp4

2.mp4