Manual Rotoscoping using Shapes

Hello!

I’m trying to do some rotoscoping for a video, just to add some neat effects. However, I can’t seem to figure out how to animate the vertex change of a shape the way I want; all the tutorials I’m able to find are for a slider-type shape change using relative shape keys, but this only tweens between two shape keys. I need to have hundreds of keys, at most one for every frame. Also the only tutorial I could find was for pre-2.4 blender, and it uses different shape key methods!

Is there any way to do such a thing in Blender? Thanks!