OKay so you know if you crop your screen so that maybe 20 % of the video is shown in the middle of the screen, and the rest is black. then as the video plays it grows from that 20% to the full hundred % while the video is playing.
i foregt how to do this
can anyone please help?
If you just want to crop you could animate a mask.
Another way would be to create a comp sized solid, put the solid above your video layer, make it an alpha track matte for the video, then scale the solid from 20% to 100%
Hope this helps.
Depends on what you are looking for. For a letterbox stripe, CC Jaws would work. Set the Height to zero so it has no teeth, then apply an Invert effect afterwards and set it to Alpha. For a square box, CC Grid Wipe could be tweaked. For perfect control and maximum flexibility, use masks or matte layers as Rick suggested. For Alpha mattes, I recommend you use a shape layer rectangle, since it's parametric and may be easier to control.