I am on Ubuntu 14.04.3 32bit platform. I want to compile opencv, it requires libavcodec-dev. I want to install it but it needs a long list of packages. It would be easy if I could just install them all with just one click. Unfortunately I encounter conflicts of packages now. Because I installed libavcodec-extra-54 in the past and it's not compatible with libavcodec54 which is one of the packages libavcodec-dev needs. I attempted to remove libavcodec-extra-54 naively, but it listed dozens of applications to be removed.
IIRC I encountered the same problem while switching from libavcodec54 to libavcodec-extra-54 but I don't remember how I managed to install libavcodec-extra-54 in the past.
I need that know-how to revert it now but I don't remember now. I hope anybody knows how to manage what I encounter.