This morning I updated my desktop. When I returned, I soon discovered that wmv files would no longer play in VLC or Mplayer. Apparently the file libx264.so.78 no longer existed. Thus began one of those searches that Gentoo sometimes subjects me to, a search to find out why something no longer works (which unfortunately isn’t always tied to an update, but instead just happens).
Today, luck was with me. I was able to find a reference to a tool called revdep-rebuild (on the Gentoo Forums). Looking up the tool on the Gentoo documentation page revealed it to be a part of a package called gentoolkit, which contains a number of programs that essentially act as a supplement to portage.
This tool’s function is simple - it figures out what dependencies portage missed when it updated, and emerges these properly.
To install revdep-rebuild, run the command
emerge gentoolkit as root.
To run revdep-rebuild, simply enter its name. With luck, you won’t have to mess about with the options, and simply running it will work.
For more information, see the Gentoolkit’s Gentoo Documentation Page