That is more what I was going for, the point is it should just work if the codecs are installed on the system, no matter how they are installed, be it individually or as a package.
What exactly should just work? The term "video" in your first post in this thread is too vague. Obviously you are aware about the different encoding and file formats, but for some reason don't give any information about the formats you use and the DirectShow filters that should be used from the K-Lite Mega Codec Pack.
VLC does not use the DirectShow filter system at all. It uses only internal codecs because it is a multi-platform player. MPC is fully DirectShow compatible, but it uses a few internal codecs by default.
MC is designed to use the externally installed DirectShow filters and by default the filters are selected by using the DirectShow merit system. Have you checked that the installed filters have correct merit values? (= the preferred filter has the highest merit of the filters that support the format or task). MC provides good tools for overriding the automatic merit system if and when preferred.
JRiver Wiki has an article about DirectShow playback:
http://wiki.jrmediacenter.com/index.php/DirectShow_Playback_Guide. Wikipedia provides some good info about the DirectShow system in general:
http://en.wikipedia.org/wiki/DirectShow. There is also a chapter about "Codec Hell":
http://en.wikipedia.org/wiki/DirectShow#Codec_hellThe quite minimalist CCCP pack is often recommended here because it pretty much
just works with the most common encoding and container formats when no other filters are installed besides what MS provides by default. My preferred method is to first install only CCCP and then install additional filters only if necessary, one by one. This makes possible to test each installed additional filter individually and it is easy to uninstall the last installed filter before trying some other filter.
EDIT
I changed most of the "codec" words to "filter". Filter is more correct when we are speaking about the DirectShow system.