The gst-ffmpeg module for the GStreamer 0.10.x series has been renamed
to gst-libav for the GStreamer 1.x series. Both use libav internally,
it just did not seem a good idea to change the name during a stable
series.

The 1.x versions of this module can be found here:

http://gstreamer.freedesktop.org/data/src/gst-libav/

(The git repository of gst-ffmpeg and gst-libav are the same,
there is a symbolic link server side. The gst-ffmpeg version
can be found in the 0.10 branch, and gst-libav in git master
and the 1.x branches.