How would an extraction from general footage be done. The footage doesnt have a large amount of contrast between the character and the background but i need to do this for only about 20 frames and wouldnt mind keyframing it but am unsure about how or where this is done. I could use the erase tool but that isnt meant to be keyframed (or is it?) any help or direction would be appreciated.
You'll want to learn about rotoscoping. You'll find a great explanation at Scott Squires Effects Corner Blog in his
Rotoscoping Part 1 and
Rotoscoping Part 2 articles. You'll find an explanation there and if you click on the title of each article you'll find movie tutorials that show the technique. He used a different app (commotion) to do the actual masking, but the technique is the same in After Effects.
The short and simple answer is that you'll just animate some masks.
ok i have a method down where i use the pen tool and move the vertices at each frame or after a few frames and that way i can mask the object in question from the background, but i would like to figure out how to do it with the eraser tool if possible and not by ctrl-shift-D'ing at each frame so that i can start a new eraser drawing, there should be some way that it knows that i want each frame to be a new drawing (or erasure)