To discover which plugin is used for specific file run command similar to this:
gst-launch -v filesrc location=filename_here ! decodebin ! autoaudiosink
that should give you (among other things) output lines similar to these:
...
/GstPipeline:pipeline0/GstDecodeBin:decodebin0/GstTypeFindElement:typefind.GstPad:src: caps = application/x-id3
/GstPipeline:pipeline0/GstDecodeBin:decodebin0/GstID3Demux:id3demux0.GstPad:sink: caps = application/x-id3
Pipeline is PREROLLING ...
