Write replaygain_album_gain instead of REPLAYGAIN_ALBUM_GAIN

[jimbo27]

Beets seems to write replaygain tags in upper-case.
There are music player in the wild which only understand lower-case replaygain tags (Poweramp, KODI).

Is it possible to write lower-case replaygain tags instead of upper-case tags with beets?
For example replaygain_album_gain instead of REPLAYGAIN_ALBUM_GAIN ?

[sampsyo]

This would be an issue for MediaFile, which is our tag-name abstraction layer. However, it actually does already store both tag names, as you can see here:
https://github.com/beetbox/mediafile/blob/edc64145e9e96624f8a77fd3cb929891c946d4dc/mediafile.py#L2202-L2209

Perhaps the problem with those two tools is elsewhere?

[jimbo27]

What I tried: I have completely deleted the ReplayGain tags from a series of files with zero and checked that they are really gone in the library (info) and the mp3 files. After that I re-tagged them with replaygain (replaygain). After that I found the ReplayGain tags again, only in upper-case.

[sampsyo]

Terribly weird! Thanks for trying all those things… I have to admit I'm stumped at this point. I don't see why this would be misbehaving in this way. I'm honestly not sure what to try next!

[jimbo27]

I tried something else.
I changed the lines of code in mediafile.py to see what tag is written. After applying scrub and relaygain again, I suddenly found two tags in my file, although with different names.
So when both are named differently, all of a sudden both show up. If both have the same name but are capitalized differently, they don't show up. Is this a bug?

[sampsyo]

Wow; that is very interesting! It may indeed. If it is, it would be a bug in MediaFile or the underlying Mutagen library. Any chance you could file a bug there with instructions about how to reproduce the problem?

[jimbo27]

sure! -> done!
beetbox/mediafile#62