Need only a moving character to not be keyed
 

Ok I filmed this last year so I have to use what I have. We were in the woods, I left the camera static. 1 by 1 I had 3 actors walk towards the camera, each in a different 3rd of the frame. What I want to do in essence, is make them fade in 1 at a time. I am trying to think of how to do it in AE CS3. I figure I need to find a way to to key out anything that is not moving between the static background, and each of the characters walking, even if I have to do them separate and overlay them later. The first step is to figure out how to accomplish leaving just the moving characters and keying out whats behind them. Any ideas?

Assuming that the background is fairly static, if we take the character that is in the rightmost part of the frame, duplicate the portion of the clip where he/she is not there, say the part where the leftmost character is in the scene. Apply a simple mask to the duplicated clip to oly show the background. Animate the opacity of the clip to fade out, that will reveal the clip underneath, where the character is.

i do want to try and get a tighter mask more around just the character that is moving because then I can fit them tighter together later. When they get close to the camera they are close (but not overlapping) in frame as well...so its a bit tricky. A simple mask would likely end up cutting off pieces of arms and stuff as they are in full motion, moving arms, legs, body etc.

Well, in that case I think you need to rotoscope them.

Track mask. Most people say it doesn't work, but I've used it successfully. The results generally require additional tweaking: matte chokers and such.

First you build a 'background' layer that only has your BG elements. You need to find a frame that best matches the BG in the footage with the talent. Then you time-stretch that frame to the duration of the live-action footage and apply --and fill in the blanks in-- the Track Matte effect dialog.

The match between your BG plate and your footage's BG will never be perfect, so some pixels will key-out, and others may not. What you want is to set the sliders so the bulk of your actor is still there, while the bulk of the BG is gone; a peppered appearance in the BG-key is okay, and a few small islands of transparency in the actor is okay. Then apply a matte choker-- this will 'heal' the pepper and islands-- and tweak that so the balance is acceptable. It also helps if you mask out the parts of the frame that are irrelevant, less visual noise to confuse the tweaking process.

This will be very difficult if your BG is live, i.e. wind blowing leaves and branches. Interlaced footage presents its own set of problems.

I tried it, but it didn`t work for the footage since the leaves were making crazy patterns with the sunlight etc. Is there a faster was of rotoscoping other than cutting out 24 individual frames per second?

In many cases rotoscoping doesn't need to be done frame by frame. every 5 frames, depending on the amount of movement, is a good starting point with specific adjustments where necessary

You could also try "Auto-Trace" in the layer menu, but there has to be good contrast in the image. And it takes a fair amount of messin' with to understand the settings. PM me if you'd like me to try some things.