I faced a problem where loading the libav GStreamer plugin resulted in a segmentation fault. The problem is that some plugins (libcdio) might have a NULL long_name field in their structure.
I figure this out when I tried to implement a GStreamer pipeline in a Gazebo plugin. Gazebo is using libav.
You can reproduce the bug by calling avdevice_register_all() before implementing a pipeline using an "avenc_mpeg4" element.