3ivx D4 4.5 has been released. It consists mainly of two parts:

• The 3ivx Filter Suite for Windows which consists of filters for encoding and decoding of MPEG-4 audio and video in MOV, MP4 or other containers.
• 3ivx for QuickTime for Mac which is an MPEG-4 video codec that integrates with QuickTime.

Personally, I've been looking forward to this; It's the best and fastest decoder for macs. It's also nice that there will be a simple way of playing MPEG-4 files on Windows, so you can convert AVIs to MP4 or QuickTime, and just tell Windows users to get this.

I'm looking forward to trying it out when I get home - and it'd be nice to hear what Windows users think of it

For MPEG4 audio encoding they use recent FAAC, and for audio decoding their own decoder which is not based on FAAD2, but does decode AAC-HE and AAC-HE multichannel.
Last time I tested their latest alpha audio decoder (few weeks ago) it was clearly slower than FAAD2 though, but otherwise working.

It's because it is based on CT's libraries, which are less optimized than libfaad2

in new 3IVX they use FAAC 1.23.3... please tell me where did they get it? my latest version 1.23.1.

Remember to uncheck the codecs in the Directshow Priority tab if you already have divx and xvid decoders installed.

Perhaps you should compare their decoder to XviD and DivX. It really is quite good - and neither the DivX decoder nor the XviD decder is all that fast, actually.

Fast? Maybe. But the picture seems to be little bit too bright