RadicalEd0 wrote:<bites his (her? o.o) head off> no just kidding. Don't worry, you can post stupid questions here, this isnt doom9. Don't post stupid questions there.. people will yell at you. But here everyone can act like a fool freely because.. this isnt doom9. So don't worry. But anyway...
DivX isnt a player, its a compression format, just like mpeg 1, but its usually used to compress avis. It's actually just a hacked version of microsoft's third mpeg-4 codec, which sucked anyway, and thus DivX 3.11 alone still pretty much sucks. Actually, there were two DivX codecs, a high motion, and a low motion, but both sucked. But see this guy realized that you could play around with DivX's quantizers and crap and combine the fast and low motion codecs and thus SBC was born and so was Nandub. Nandub let you tweak DivX until it looked decent, in fact until it looked good. So good that you could encode half hour anime episodes at a size of 100 megabytes with good quality. Eventually DivX 3.11, the hacked version, was abandoned and an openDivX project (project mayo) was started. The aim of this project was to build a completely legal variant of DivX 3.11 using original source (and not that of M$). Some different codecs spun off of this, 3ivx, XviD (will come back to) uh.. something, i dunno, mostly crap. And DivX 4, which was released by DivX Networks. It kinda sucked, but it was a start. A lil while later they released DivX 5 which was a lot better and about as good as DivX 3.11 with SBC. In the mean time XviD was beating the crap out of DivX 4 and the other openDivX codecs, and now DivX 5 and XviD are about evenly matched. Jeezus that was boring to write, but there, now you have the entire history of DivX, yeesh.
I'll attempt to give some better information than the person above.
DivX 3.11a offers very good image quality for its size. It is, quite simply, a hacked MS MP4v3 codec which allows more compression options than MS MP4v3.
MS MP4v3 is a derivative of MPEG-4. It is not a true MPEG-4 codec - Microsoft only implemented a small chunk of the features in the ISO specification. (Enough to give good compression, but not enough that they'd have to pay royalties for their encoders, I'd imagine...)
DivX 3.11a is two codecs - "Fast Motion" and "Low Motion." The Low Motion codec offers superior quality over the Fast Motion codec, but the Low Motion codec doesn't always handle fast motion sequences well at a low bitrate.
To solve the problem, DivX 3.11a SBC basically uses both the Fast Motion and Low Motion codecs in the same file. 2-pass variable bitrate encoding is used to ensure that the video is allotted more data where it needs it (sequences with a lot of movement) and less data where it doesn't (still pictures, black screens, etc.).
DivX 3.11a SBC is, to my knowledge, the best implementation of DivX 3.11a.
However, a small but growing company wanted to capitalize on DivX's growing popularity. One problem - it's a hacked codec. DivX 4 was created legitimately, so that legitimate stuff could be done with it. However, it still had flaws, and it still wasn't a true MPEG-4 implementation.
DivX 5 Professional is a complete and (theoretically) stable implementation of MPEG-4. The free DivX 5 is also MPEG-4, but it has some features removed and wouldn't allow for the same quality as the Professional version.
A few open-source MPEG-4 projects exist, but the one standout MPEG-4 codec is XviD. (Yes, it's DivX spelled backward.) Many people agree that XviD offers superior quality over DivX 5, and the fact that XviD is free doesn't hurt, either.

However, XviD is still in the Alpha stage of software development - meaning it works, but it doesn't yet have 100% of its features implemented. Fortunately, even the early version out now is true ISO compliant MPEG-4, meaning you can make "mp4" video files with it and an MPEG-4 decider will understand it.
As XviD further develops and is completed, there's a good chance it'll dwarf DivX 5. Fortunately, as both follow the MPEG-4 standard, they each should be able to play back the other's content (if the content is properly made).
<I>No version of any of these codecs sucks.</I> Some are better than others, yes. DivX 4 is basically considered useless these days, and DivX 5 might not be all it's cracked up to be, but DivX 3.11a was excellent at the time it came out, and there are worse things you could use than DivX 5.