Does it matter, since the game is being sold for real money and they can well afford to license an audio codec? It's not like they're planning on releasing their games as free software under the GPL or something.
Our existing Miles license makes it easy to use an mp3 for playback, I don't see it being worth the engineering effort at this time to re-encode all the music and add the extra code and dependencies.
You would not have to add extra code and dependencies, but replace existing ones with other code and dependencies.
Since opus is a free (as in freedom) codec, better coders/decoders can be written.
Also opus provides a generally better quality/size ratio than many other audio codecs including mp3 and allows using lower bandwidths for VoIP.
Nothing extracted yet.
i just saw the license note in the audio tab in hl blue shift...
suggestion: reconvert mp3 to ogg/opus and try to use free software wherever possible.
see http://www.opus-codec.org/
if you won't change it for the existing games, consider using it for e.g. ricochet 2.