Q: What is the different between DivX4 and DivX3 / DivX ;-)?
A: DivX4 is a new MPEG-4 codec developed from scratch by DivXNetworks:
http://www.divx.com/. It offers different encoding modes like quality based and 2 pass encoding and it can play back the old DivX3 files. DivX3 is a hacked version of the Microsoft MPEG-4 v3 codec which initially only could be used in the windows media encoder and only to create .asf files.
Q: What is the best way to create a DivX3 file?
A: Nandub. Nandub is the most advanced DivX3 encoding utility. It uses a 2 pass procedure and changes the bitrate on the fly for every frame to achieve optimal quality and complete size predictability. As Nandub is very advanced there's an easy to use frontend called GKnot which uses Nandub but hides most of the hard to understand options from you. Another easy to use program that gives good results is Fair Use. This one encodes a movie multiple times, then merges the encoded files based on a quality measure.
Q: Can I use FlaskMpeg / Xmpeg to do 2 pass DivX3 encoding?
A: No. Nandub is required.
Q: Where can I find a more detailed FAQ?
A:
http://www.doom9.org/faqs.htm