[Cellar] Conversation about a NON-IANA request in Matroska

[Spencer Dawkins at IETF <[e-mail]>]

Hi, Murray, the backup expert reviewer for Media Types, and our responsible
AD,

Cellar is working on the Matroska specification, and one issue we've
tripped over is that Matrosks implementations have traditionally used
unregistered MIME types such as "video/x-matroska" and file extension
".mkv", which have never been registered in the Media Types registry, and
(for extra credit) use "x-dash" notation that someone is likely to ask us
to change, if we were registering something now.

Specifically, the media types mentioned in
https://github.com/ietf-wg-cellar/matroska-specification/pull/529/files
have been in use for up to 19 years, and the sense of the Github discussion
is that actually registering them now won't have much impact on anything.

(You should be tagged in that PR, and that's where most of the discussion
I've seen has happened)

And we'd prefer not to start that conversation during AD Evaluation, IETF
Last Call, or (especially not!) during IESG Evaluation and formal IANA
review.

As this work moves forward in the IETF stream, we wanted to ask, is this a
thing we should talk with you about, sooner rather than later?

Best,

Spencer