FAQ: Why is my output file huge, and why doesn't it play back smoothly in a media player?

(For a video version of this frequently asked question and answer, click this link.)

When you render and export a movie, the default ouptut settings are for files that are not intended for playback. The default on Mac OS is for a QuickTime movie with lossless Animation compression. The default on Windows is for an AVI movie with no compression. An uncompressed or losslessly compressed movie is huge and is not intended for playback; it's  intended as an intermediate file for further post-production work. These  huge files can't be read from disk fast enough to be played in real  time by some computers. For smooth playback on your computer, you need  to compress the file. See this page: "Encoding  and compression options for movies"

Movies are compressed differently depending on how they are to be  used. When they are intended as intermediate files (i.e., as input into  another piece of post-production software), they are compressed very  little. That is the default from After Effects because After Effects is  primarily meant as a compositing, motion graphics, and visual effects  tool, and it feeds into other tools, like non-linear editors. If, on the  other hand, the movie is intended to be played back from a DVD or  distributed over the Web, then the movie is compressed a lot---and in  one of many, many specific ways.

The upshot is that you really need to begin  by knowing what it is that you want to do with the movie. And then you  need to learn about what output options are best for that purpose.

There's a  good article from Aharon Rabinowitz linked to from this  page that talks about how you need to be thinking about the details  of output from the very beginning of a project.

For information about choosing output settings, see this page: "FAQ: What is the best output format for rendering and exporting from After Effects?"