The first thing you want to do is to film your base footage.My footage is a simple tripod shot of Celina from Fables in Fashion doing a spin at the edge of a pier.
I was so silly as to forget to take a clean shot of the scene without Celina in it. This was a bad oversight, since I knew I wanted her to dissolve which means I need at least one shot of the empty scene.
So I spent about 2 hours cleaning the footage and removing Celina from the shot using the clone stamp and a number of masked out layers. I also decided to remove some other objects from the scene like the boats and the shadow of the lamp post on the wooden beams.
Note that due to the cloned water, there are a few spots that look a little strange if you look at them closely. However, since the clean shot will only be shown for a few seconds in the final VFX, this is not a big deal.
Next, I used the roto brush tool in Adobe After Effects to rotoscope Celina and create a clean video layer with an alpha channel.
Since we will add this overlay on top of our clean plate, the rotoscope does not have to be 100% spot on, just good enough to define Celina's shape as she is spinning and dissolving into crows.
The next step is to set up and create the crows in 3dsMax!