[dvd::rip] Resulting avi is much smaller than target

[Florian Lindner <mailinglists@xxxxxx>]

Hello,
I've ripped and trancoded an DVD using the following settings:

[General]
Title:                 Doom
Data source:           DVD
DVD title number:      1
Runtime:               01:48:07

[Video]
Video format:          PAL
FPS:                   25.000
Size:                  624 x 272
Video bitrate (kbps):  1413
Video codec:           xvid
2-pass-encoded:        yes
Fast resizing:         yes
Deinterlacer filter:   
Antialiasing filter:   Kein Antialiasing

[Audio 1]
DVD audio track id:    1
Language:              de
Audio codec:           mp3
MP3 quality:           2
Channels:              2
Sample rate:           48000
Audio bitrate (kbps):  128
Volume rescaling:      1.241
Audio filter:          Keine, nur Lautstïkenmaximierung

[Programs]
dvd::rip version:      0.98.1
transcode version:     1.0.2

The target file size was set to 1200 MB. The resulting file is only 750 MB. 
The vob files which make this chapter have a size of 5,3 GB.
Why is the resulting file so much smaler than the target?

Thanks,

Florian