Video Conversion - output file size

[Leo48]

Joining some MOV files to one AVI file, I get enormous differences in size of the output files:

Input (3 MOV files): 76 MB
Output:
SUPER 17 MB
Avidemux 68 MB
Digital Video Converter 106 MB
(the latter http://www.protectedsoft.com apparently produces a packed bitstream)

All encoded with the same settings: MPEG-4 ASP Xvid, MP3. My fault, or is there another expalantion?

[Baldrick]

The output file size depends on the video and audio bitrate settings.You can choose the average bitrate and get the exact output file size you want or quality based bitrate (higher quality=bigger file size) but you don't know how big the output file size will be then.

[jagabo]

file size = bitrate * running time

Since the running time is fixed, lower the bitrate to get a smaller file.