QuickTime is particularly efficient when using data types such
as text and still images. It sends the image only once, even though
the movie plays at 30 fps on a fast computer. The text is sent as
ASCII text with descriptors--the scrolling and compositing are done
at run time on the playback computer.
The movie is 20 seconds long, but only 24 KBytes in size.
A similar movie rendered by a compositing program such as
AfterEffects would be at least 100 times larger.