zero: Remove tags instead of setting them to null

This issue was automatically migrated from Google Code.
Original author: adrian.sampson (December 21, 2012 06:31:58)
Original issue: http://code.google.com/p/beets/issues/detail?id=478

[mineo]

Was there ever any progress on this? I've now used some dirty hack (namely, if not val: return in MediaFile.set) to achieve not having empty tags in my files but I'm not sure that fits into beets' overall architecture .

[sampsyo]

No, I haven't looked into this in a while -- although the implementation should be straightforward except for dealing with cross-format compatibility in the Mutagen API. Therein lies the most helpful thing we could do now: add __delete__ to MediaField and its related classes and experiment with a few different formats to make sure Mutagen behaves as expected.

[bossanova808]

Just further on our replaygain chats - tried with a flac just now and these RG tags are set to 0s which is very wrong and results in very loud playback.

@yevgenybezman I presume you are factoring this in to #598 - pretty essential in this case as this behaviour is definitely not good.

[sampsyo]

That's a pretty good reason to prioritize differentiating non-existent fields from zero-valued fields.

[yevgenybezman]

Yes, of course.

[geigerzaehler]

This is a pretty important issue. I would like to change the MediaFile API so that setting properties to None will delete that tag from the file.

[sampsyo]

Sounds reasonable. We could also map this to del mediafile.field (i.e., the descriptor's __delete__ method) in case setting to None causes problems with existing code.

[geigerzaehler]

With 7b954d9 this works now for the ReplayGain fields. We are on our way to make it work for all fields.

[sampsyo]

Awesome. I'm still not 100% sure whether we want to remove null-normalization in all cases for all fields since it's incredibly useful to know that item.title is always a string. But that doesn't preclude removing tags in the zero plugin nonetheless (by interposing on writes).