I am having the same issues as well. Macbook Pro OS X Lion (latest OS stable version), i7, 8GB Ram 500GB HD.
Everytime I try to open any video in Quicktime it freezes horribly. A force quit is needed to kill the program. My main video file i'm trying to open is .MOV which should open fine in Quicktime and it is failing horribly.
Anyone have any suggestions?
I repaired disk .. repaired permisssions ... still problem is there.
Found the Answer even though you might not like the result.
Upon looking for every backdoor solution to this issue, There were many areas of this site and other websites saying to just boot into the Recovery HD partition and re-install the OS. About an hour and 30 minutes later after reloading the operating system and it not causing any issues, it fixed the problem.
Quicktime works perfectly. No issues with video playback. No hanging Application nor does it CACHE broken files or anything like that. I would have to say the problem lies in the 'return application to past state' that is built into the operating system that you can turn off but i dont' want to turn that off becuase its a useful tool.
So Re-install of the operating system solved the issue!
I had the same exact problem. Been dealing with it for about 2 hours now. Almost downgraded to an earlier version of Quicktime, but here's what I found instead:
Check if you have a DivX codec installed. Apparently there's a problem with DivX being compatible with Quicktime on Lion. If you do have a Divx; uninstall it.
I uninstalled divx and installed Perian and it's working just fine for me now. Hopefully that works and you won't have to completely re-install the operating system. If DivX isn't the problem, then I'm not sure what to tell you.