There are some codecs already packaged for gstreamer and sailfish on openrepos.net. But unfortunately I did not have time to test them yet.
I really don't think that it makes sense now to start porting old gstreamer 0.10 codec support. I rather would simply wait until jolla updates gstreamer to 1.0 which should bring in better codec support. (I know Jolla will not package codecs they don't have a license for, so will still need some extra codec packages to be build most probably)