This workaround was only relevant some time ago while custom kernels did not yet have updated sources from Samsung to work on 4.0.4 ROMs. This is no longer the case so this info is completely irrelevant now.
There are plenty of people complaining about camera and video playback problems when using custom kernels on the newest 4.0.4 builds such as XXLQ5 or XWLPM .
I tried a few things and managed to find a fix for it.
Just take the CWM zip file and apply it on your ROM. It will leave a backup of the 2 files that will be replaced.
The Restore zip can be "installed" to remove the patched files and put back the original ones that were kept on your device.
Tested and working both for Camera preview and Video playback, on XWLPM.
Note: This is a temporary fix until the kernel devs have enough information to properly update their code, and when that happens this fix can be uninstalled.