the Codec Delay header field is lost during remuxing; except for opus, of course, because of this line. I actually thought that you had a generic solution for Codec Delay. After all, this field is not restricted to opus, is it? The specs don't forbid it and the header editor lets me set it for AAC and AC3, so if it is restricted, this is a bug in the header editor and an omission in the specs. By the way, both MPC-HC and VLC seem to handle this element for non-opus audio just fine (if one uses very high values, one needs to set the number of buffered packets/seconds high enough, but that's it), so I don't see a reason to restrict it to opus.
Thanks in advance.
Matroska reader: keep existing codec delay track property