Re: [PATCH] Add: tracktag interface and support for Opus

[Grant Shoshin Shangreaux]

Yoni Rabkin writes:

> That puts us in a dilemma since other info backends, such as exiftool,
> can be used to write as well. So we either name everything which calls a
> backend to work with info, reading or writing, in the -info- namespace,
> or we split read and writing into separate namespaces.
>
> Unless people have a strong opinion either way, I'm going to ask that
> reading info be in the -info- namespace and writing in the -tag-
> namespace. Which would require you to change emms-tracktag.el and its
> various code references to emms-tag-tracktag. This way we could later on
> write emms-tag-exiftool.el and others like it, with emms-tag-editor
> being the "frontend" to these.

i've moved the tracktag module to emms-tag-tracktag.el and changed it so
that the date will write the date tag (instead of year as i had
before). i've written tags to a few files, and it appears to be working
fine so far. there are a couple of additional tags that tracktag is
capable of writing, though i haven't come across emms-info tags that
correspond to them:

--catalog=NUMBER
    the album's catalog number, typically indicated on its case
--track-total=NUMBER
    the total number of tracks on the disc
--album-total=NUMBER
    the total number of albums in the set
--compilation=YES/NO
    whether the track is part of a compilation
--ISRC=ISRC
    the track's ISRC
--publisher=NAME
    the album's publisher
--media-type=MEDIA
    the album's media type, such as "CD", "vinyl", etc.
--copyright=COPYRIGHT
    the album's copyright information
--comment-file=FILENAME
    a file containing comment text, for particularly long comments

for the time being, i'll just leave them out. a user could potentially
add mappings to the emms-tag-tracktag--info-fields list and write these,
though they won't show up in the tag editor at this time anyway. which
reminds me i need to work on the tag-editor code for displaying writable
tags in the editor buffer.

currently, there is tag writer code for using mid3v2,
vorbiscomment, and metaflac in the emms-tag-editor module. if we want to
start moving these out into emms-tag-mid3v2 etc, i'm happy to do that,
but it isn't the top of my priority list with limited time. also, i
think it could use some thought and input on how to structure the code
between various "writer" backends and "reader" backends which may or may
not be the same program.

let me know if there's anything further to add to this opus-tags branch
(which is really more aptly named tracktag-writer). i plan to move on to
working on tag writer validation next.

-Grant