If there's support for wma in gstreamer I would like to add that the following converts wma to ogg vorbis:

gst-launch-0.8 filesrc location=path-to-file/name-of-file.wma ! spider ! vorbisenc ! filesink location=path-to-file/name-of-destination-file.ogg

for mp3 conversion replace vorbisenc with lame bitrate=128 and of course change postfix to mp3.
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