Beets not writing vorbis comments to FLAC files when modifying

[zigarrre]

Problem

Beets doesn't write tag modifications done via beet modify into the files.

I tested it with FLAC files and the tags PERFORMER, COMPOSER and DISC all with the same result, so I assume it is independent of the tag.

Steps to reproduce

beet modify -wy title:'foo' PERFORMER='bar'

checking with metaflac

metaflac --list "$(beet list -p title:'foo')" | grep PERFORMER

prints

    comment[0]: PERFORMER=

should be

    comment[0]: PERFORMER=bar

Setup

% uname -a         
Linux desktop 4.8.3-1-ARCH #1 SMP PREEMPT Thu Oct 20 19:53:59 CEST 2016 x86_64 GNU/Linux
% python2 --version
Python 2.7.12
% beet version     
beets version 1.3.18
no plugins loaded
% pacman -Ss beets 
community/beets 1.3.19-1 [installed]
    Flexible music library manager and tagger

% beet config
ignore_hidden: no

paths:
    default: $albumartist/[$year] $album%aunique{}/$track $title
    singleton: Non-Album/$artist/$title
    comp: compilations/[$year] $album%aunique{}/$track $title
    albumtype:soundtrack: soundtracks/[$year] $album%aunique{}/$track $title
mpd:
    host: localhost
    port: 6600
log: ~/.beets_import_log
library: ~/.beets_musiclibrary.db
replaygain:
    backend: gstreamer
    auto: yes
    overwrite: no
    noclip: yes
    method: replaygain

ui:
    color: yes
directory: /media/sda2/music

import:
    copy: yes

[sampsyo]

That's because beets doesn't have a PERFORMER field, and we don't directly store every field as a Vorbis comment with the same name. Instead, you've set a flexible attribute that resides only in the beets database.

Can you try this with some field in the output of beet fields and see whether anything changed in the full metaflac output?

[zigarrre]

OK, I noticed that beets uses lower case tag names and is case sensitive as disc and composer do work as expected. Maybe change this behavior and make it case insensitive? Vorbis comments as well as ID3 have case insensitive field names and are often written upper case.

Anyway, PERFORMER is a official tag in Vorbis comments (https://www.xiph.org/vorbis/doc/v-comment.html) so I would expect beets to write it to file.

[sampsyo]

Case-insensitive field names might be interesting! But to be clear, we wouldn't do it because of Vorbis Comments—beets's tag names don't exactly match the storage format of any particular file metadata type.

About performer specifically, please see #507 or #1547.