It seems that there was an intent in Gentoo to give separate ebuild for each gstreamer plugin. But seems that this attempt didn't work as expected: there only a few plugins covered by gst-plugins-xxxx ebuilds... Such adds more problems to the installation than it solves. More than that: gst-plugins seem behave differently in that they ignore pre-defined USE flags when it comes to "what plugins to install" - it only checks for alsa, oss and esd flags. Going back to using a single package (gst-plugins) configurable by USE variable (or some other variable) would simplify the installation and make sure more gst-plugins are available for users. Reproducible: Always Steps to Reproduce: 1. 2. 3. Actual Results: emerge gst-plugins installs only basic set. Only a few of the other plugins are available as extra ebuilds. Expected Results: emerge gst-plugins would emerge all the plugins according to USE flags.
actually there's rationale behind all this & you should look it up... it's probably somewhere in the -dev archives. The eclass has some sidenotes on it as well.