#378 Store MusicBrainz IDs in FLAC files

[James SF DeLaHunt]

Test versions and environment
X Lossless Decoder version 20151214 (149.1)
Mac OS X 10.10.5
100% reproducible

To reproduce the enhancement
1. Open a CD with XLD.
2. Retrieve metadata for the CD from MusicBrainz.
3. Rip the CD to a single FLAC file with cue sheet.
4. using metaflac or similar metadata tool, list the OGG_VORBIS metadata tags in the FLAC file.

Observed behaviour: There are no MusicBrainz IDs in the file.

Desired behaviour: I would like there to be at least MUSICBRAINZ_ALBUMID tag set to the MBID of the Release, and for each Release Artist, a MUSICBRAINZ_ARTISTID tag set to the MBID of that Artist. There should be no other MUSICBRAINZ_ALBUMID or MUSICBRAINZ_ARTISTID tags.

For example, for Release Matthäus-Passion, I would like to see the following tags in the single FLAC file each of its CDs:

MUSICBRAINZ_ALBUMID=b3d7a27b-1cb7-4c45-83cf-b4447bbcb357

MUSICBRAINZ_ARTISTID=24f1766e-9635-4d58-a4d4-9413f9f98a4c 
MUSICBRAINZ_ARTISTID=06bdfba6-40b6-407d-8ede-d77e3b94db30 
MUSICBRAINZ_ARTISTID=246fa33b-223d-45c3-98a7-fe95196492b7 
MUSICBRAINZ_ARTISTID=3c1d85a2-2915-4258-8aeb-4ccd3d06e514 
MUSICBRAINZ_ARTISTID=a5a49da8-f65f-4402-a715-1648004f9f03 
MUSICBRAINZ_ARTISTID=8113f437-ff42-4540-9250-43f763aa16ba 
MUSICBRAINZ_ARTISTID=683defe8-4b34-4238-b7b3-20595fb8545a 
MUSICBRAINZ_ARTISTID=06191759-0fa7-4870-b593-4c6c93cddd81 
MUSICBRAINZ_ARTISTID=3822ca30-d465-44c7-b178-22976d981c34 
MUSICBRAINZ_ARTISTID=6fd9e1dc-4bbc-4acc-848b-1031d6f2d26a 
MUSICBRAINZ_ARTISTID=00963f2f-a46b-409b-89a9-7b87710b39e2 
MUSICBRAINZ_ARTISTID=29ae6848-5db5-4ea5-aa87-fa944c0b3d76 
MUSICBRAINZ_ARTISTID=7badcc14-8d16-4734-acda-40645d156602 
MUSICBRAINZ_ARTISTID=9b891046-35af-4eb0-a058-eba4c9b8d01f 
MUSICBRAINZ_ARTISTID=98b95966-64db-4631-8b9f-8aa66f32cc98

Discussion:
MusicBrainz IDs provide a unique and permanent identifier for Releases and Artists. We can expect that the content of the metadata for Releases and Artists will improve over time. Names and Titles might well change. But if we have the MusicBrainz ID, it is simple and reliable to look up the current metadata in the future. (I think MBIDs might be the most valuable service MusicBrainz provides, actually.)

When I use XLD to make a single FLAC+cue file for a CD, I am trying to archive the CD. I know that the metadata is inadequate. I might have just created the Release in MusicBrainz, and I entered the minimum about the CD to make a Release entry. I know the metadata will get better. I want to be confident that my archive will make it possible to re-tag music files in the future, using the unique and permanent MBID to be sure I get the right metadata.

Other MusicBrainz IDs are less important. For instance, track IDs might be interesting when XLD rips separate files for each track. However, taggers like MusicBrainz Picard can get the right data using just a MUSICBRAINZ_ALBUMID tag, the disc number tag, and the track number tag.

To check metadata, use the metaflac tool like this:
metaflac --list --block_type=VORBIS_COMMENT