emms cache db best practices

[Grant Shoshin Shangreaux]

Hello emms devs!

I've been digging into the application and hope to contribute to it a
bit in the future. Specifically I'm trying to figure out the a good way
of editing tags on .opus files, and perhaps using the cache db for
additional metadata storage.

Unfortunately, I had an unexpected Emacs crash this morning, and
discovered on relaunching that my emms cache had lost information. After
looking through the code, it appears that the cache is only saved when
you ask it to be or if you kill Emacs.

Normally, this might not be a huge deal. Most track data is actually
metadata on the media files. I could just re-add them. However, in this
case I'd only recently discovered that the tags i'd authored for some
.opus files had not actually been saved. This set me off on finding out
why the tag editor had "silently failed" to save the metadata to the
file, while revealing the feature that the emms-cache-db could preserve
metadata not attached to the file! similarly, i'd been experimenting
with the emms-bookmarks.el which also uses the cache to store timestamps
on a track.

Anyhow, i was wondering if there might be some way to mitigate this
problem in the future that doesn't demand manually saving the cache or
killing Emacs?

If anyone has some thoughts, I'd be glad to hear them :)

Thank you,
grant