Comment 7 for bug 1460464

The package gstreamer1.0-libav is not needed for Opus support; the Opus codec is part of gstreamer1.0-plugins-bad (which is in universe currently)

And the codec is considered to be safe by major players like Mozilla, Google, Cisco & Microsoft (all relevant patents come with a royalty free license for Opus), so I'm not sure what is holding up Opus support? (Even Canonical seem to consider it safe, as it's in universe and not multiverse…)