When ever I key a green clip the edges around the object i've cut out are alwayse blocky looking and are never clean. Ive tried shooting the person from father away, I've tried moving the person farther away and i've tried lighting the person from the back but none of these help. How do I fix this?
It sounds like you're trying to key a lossy format like DV. There are a few keying tools out there that are designed to compensate for this, though the quality will always be lesser than using an uncompressed format. The newer versions of the Ultimatte AE plugins work okay, but dvGarage has made a Motion-native (meaning fast, often realtime) version of their dvMatte keyer. You can get a demo version at http://www.dvgarage.com/prod/prod.php?prod=dvmatteb&sub=samples