So what's new in DivX 4.0 Beta 3? Well, it's completely re-written to improve performance and visual quality. The code base is different from all earlier versions, including the open-source OpenDivX codec.

Bugs Fixed in the DivX 4.0 Beta 3

DivX decoder registered itself for 3.x formats even if user answered No when installing
Found one more bug in 3.x decoder
Fixed problem with quality loss when encoding at height not multiple of 16 and low resolution
Fixed crash when encoding on Pentium II / Celeron machines (accidentally introduced in beta 2)
Fixed noise problems in playing 3.x content
More accurate 2-pass VBR
Rearranged controls in encoder config dialog