About .AVI File
AVI stands for Audio Video Interleave. It is a special case of the RIFF (Resource Interchange File Format). AVI is defined by Microsoft. AVI is the most common format for audio/video data on the PC. The name "AVI" is appropriate because the audio and video data are interleaved (stored in alternate segments or blocks) in the finished file. Movies in the .AVI format are also cross-platform compatible and can be played on various operating systems.
.AVI is actually a rapidly moving series of captured bitmaps that shows movement of screen elements. The size of video captures depends on the size of the window being captured, the speed at which the "frames" of video are captured, and the duration of the video capture. To limit file size, try lowering the frame rate, eliminating extraneous elements on the captured window, and keeping the length of the capture short.
All .AVI files should be compressed for distribution, especially to the Web, because the files can become quite large.