OK you need to make sure your Flash file is at the right size and frame rate for video. Let's assume 720 X 576 pixels at 25 frames per sec. Go into modify movie in your flash file and enter the appropriate values here. Good idea to do this before animating as you may find changing frame rate midstream plays merry hell with your animation fluency. Then when you're done, export movie as PNGs or if you're less fussy, jpegs, and it will spit out a stram of stills (25 per second in this case). These can be imported into after effects and usually with a tiny bit of motion blur they'll look pretty damn good in video land.