The default for the this program is Enable audio/video Interleaving with a 500ms pre-load in VirtualDubMod,this is the recommended value, it is not an offset this is done in the Audio Skew Correction the same is true for its older cousin VirtualDub.
This will set the Audio Frames to "Split across interleaves" which can cause the audio to go out of sync with the video even if the MP3 is set to CBR
a problem most known with VBR audio on standalone DVD players that that DivX capabilities. This is one reason why the preferences are set to warn you about VBR audio this is a screendump from VirtualDub
It is said that if the AVI has Audio frames that are "Aligned on interleaves" it will always remain in sync
even with a VBR MP3 audio track.
If you experience VBR MP3 problems you can turn off the MP3 ACM and use VirtualDubMod MP3 encoder under here the default preload for AVI audio is set to 500ms as shown this is the same in VirtualDub.
If you are going to re-encode the MP3 audio to AC3 the audio gets split across interleaves with the default values MP3 seems to Align with Interleaves itself .
However if you Enable Frame Mode the resulting AC3 will get "Aligned Across Interleaves" (you can't do this tweak in VirtualDub by Avery Lee)
Options -> Preferences -> VDubMod -> AVI -> Enable Frame mode.
If you are OK with this then you can re-encode the VBR audio MP3 to CBR dolby digital AC3 audio "Aligned Across Interleaves" and know that your audio frames will be aligned with the Interleaves and AV sync problems on your DivX enabled DVD players.are over.