Bugzappy's Blog

We had a problem on some of our Macs where the iPhone simulator would not play videos that we encoded and embedded in an iPhone application that we built. However these videos would play just fine on their own, and also they would play just fine on a real iPhone, without any changes.

Apple support forum has some answers:

http://discussions.apple.com/thread.jspa?messageID=8538445

Particularly helpful:

This fixed it for me.

I moved :
DivX Decoder.component
DivX Encoder.component

out of the directory:
/Library/Quicktime
The video player used to not play files that I encoded myself. Now it does.

Thanks 

ed.anisko

I did exactly that and everything worked fine. Note: I don’t use DivX so I cannot be sure that this quick fix will not break something important to you.