That codec pack doesn't work on Windows 8.1 Pro Update 1, I just tried. The one I linked to, last, does work on mine. Of course if the OP doesn't have exactly the same Windows 8.1 as I do maybe yours will work for him.
I'm suspicious that the 70D may have installed something that makes the 7D not quite work and installing the codec pack was one way to possibly get it to work, if the OP can find the version of the codec pack that will install and not report that it is not applicable to their OS version.