Someone

   <RDF:Description RDF:about="urn:mimetype:externalApplication:application/mp3"
                   NC:path="/usr/bin/xmms"
                   NC:prettyname="player" />


  <RDF:Description RDF:about="urn:mimetype:application/mp3"
          NC:fileExtension="mp3"
          NC:description="Music File"
          NC:value="application/mp3"
     <NC:externalApplication RDF:resource="urn:mimetype:externalApplication:application/mp3"/>


from gu1om
la liaison :

  <RDF:Description RDF:about="urn:mimetype:externalApplication:audio/mpeg"
                   NC:path="/usr/bin/xmms"
                   NC:prettyName="xmms" />

et la description des mpeg :

  <RDF:Description RDF:about="urn:mimetype:audio/mpeg"
                   NC:value="audio/mpeg"
                   NC:editable="true"
                   NC:description="">
    <NC:fileExtensions>mp3</NC:fileExtensions>
    <NC:fileExtensions>mpga</NC:fileExtensions>
    <NC:fileExtensions>mp2</NC:fileExtensions>
    <NC:handlerProp RDF:resource="urn:mimetype:handler:audio/mpeg"/>
  </RDF:Description>