Of course I'd like it if the interface to the metadata was identical
to that in the Ogg Vorbis encoder...

That'll always happen as much as possible. We just need to document
that, e.g. the names that we use ("title" for title? or "name" or
"Title"? or ... - etc.).

Currently, mad, vorbis, avidemux handle metadata, they explain some of
the names used in the name/value pairs.

no, consistent metadata handling should be done at a higher level.
It's not a good idea to have the same low-level interface to vorbis
and id3 metadata since they're fundamentally different.

Is that a good idea? It seems to me that it's best to provide an
interface that's as uniform as possible. The result would otherwise be
that every player needs to duplicate code for metadata and most will
probably do it wrong.

Or do you think it will work out fine? And if so, how/why?

b/c we should have a metadata library above the plugin level that
unifies this

*** This bug has been marked as a duplicate of 116420 ***