Hi, I've filmed a lightsaber duel and just finished rotoscoping one of the lightsabers for the entire film. I rendered it and saved it as a avi file. When I watch it in windows media player, the frame rate is slow and choppy until I watch it like 3 times, then it's pretty smooth. I want to render it so when i watch it, its always smooth, like the lightsaber is really part of the movie, and it's not slowing the movie down. Any help?
I'm guessing that you rendered and exported an AVI file with the default settings. The default is for an AVI file with uncompressed video. Uncompressed video files are huge, and reading the frames from the disk is slow, so your media player struggles when playing them. (The playback speeds up after the media player has cached the frames for playback.) Uncompressed files are not intended for playback; they're intended as an intermediate format for further post-production work.
As a beginner, I suggest that you begin at the beginning: "Getting started with After Effects"