The new IETF-approved audio codec opus comes in ogg files with the .opus extension. It should have an audio/ogg mimetype. See: https://wiki.xiph.org/OggOpus#Content_Type As our mime.types uses entries from debian, you can also re-sync with their mime.types: http://anonscm.debian.org/gitweb/?p=collab-maint/mime-support.git;a=blob_plain;f=mime.types;hb=a100b97ae32895e58db1150a00c633e83c101d05 They just added it.
Fixed in mime-types-9.