[ID3 Dev] User-Defined Frames

John Slane jaslane64 at yahoo.com
Sat Mar 3 14:03:17 PST 2007

As you will be able to infer, I am pretty much a newbie to mp3 and ID3.  I am about to begin tagging a few thousand mp3 files, and I sure would like to get it right the first time.  I've read through the ID3v2.3 standard and I have experimented with modifying tags using mp3Tag and MediaMonkey.  I look at how each program modified the tag by reading the tag with id3.exe.  While I believe I understand the basics now, I have a couple of nagging questions that remain, and I hope that you can kindly help me out.

I want to use tag metadata to build "AutoPlaylists" in MediaMonkey.  Basically, I'd like to be able to tell my jukebox - for example - to play songs from 1968 that have the Genre = Soul or Funk AND the Theme = Cars or Dancing.  This idea raises a few issues:

(1) A TCON (genre) frame in ID3v2.3 is defined as a numeric string.  I notice, though, that both MediaMonkey and mp3Tag write alphabetic words into this frame (as confirmed by id3.exe).  Is this in conformity with the spec, and might it cause any problem with reading the tag in other programs?

(2) Although only one TCON frame is allowed per tag, I was able to write multiple genre values into the TCON frame, simply by writing them as a string, delimiting them with spaces or other characters.  MediaMonkey is able to then search on any portion of the string to make a playlist.  Is there any potential problem (with any tag-reading software) that arises from putting multiple genre values into the single TCON frame?

(3) Now I come to my "Theme" field.  Since there is no declare Theme frame type in ID3 and no Theme field in MediaMonkey, I could sneak "Theme" values into one of MediaMonkey's predefined fields that I do not use; but it would, of course, be mislabeled.  On the other hand, I could put my "Theme" values into a TXXX or a COMM frame.  MediaMonkey does not create or recognize any TXXX frames, but it does offer a few user-defined COMM fields (Custom1 - Custom3).  So I could use one of these, and use the Descriptor "Theme," and enter my multiple-valued theme data in as a string, with whatever delimiters seem appropriate.  Does that make sense?  Are there any kind of rules for choosing delimiters, in terms of compatibility with the world of software out there?

(4) When I do use one of MediaMonkey's "user-defined" COMM fields, I note that MediaMonkey imposes its own descriptor on the tag frame.  For example, if I enter "January" into user-defined field "Custom 1",  I get the following tag frame:
COMM = Songs-DB_Custom1  January.
So MediaMonkey has predefined descriptors that it uses for its "user-defined" fields/frames.  These fields seem to work just fine within MediaMonkey, for making playlists, etc.  But will they cause problems for me in the future if I migrate my music collection to another jukebox software or some other software application?  I fear that using the MediaMonkey jargon in the tag will cause me recognition problems elsewhere.
(5) Considering Issues (2) and (3) together, I wonder about the difference between a text frame and a comment frame.  For example, how are a TXXX and a COMM actually different (so I know which to choose for what).  Each one can have multiple occurrences in the same tag; each one takes a descriptor to distinguish it from its kin in the same tag; and each one accepts a text string as its actual data.  So how are they different?  Does one allow a LONGER string, or broader formatting, or what?  I'd like to know when a TXXX is appropriate, and when a COMM is appropriate.

As you can see, I'm trying to figure out how to cram non-standard information (multiple genres, music themes, months of the year) into my ID3v2.3 tags.  And my current jukebox (MediaMonkey) apparently gives my a couple of options for doing this, but they seem rather limited, and I worry that using them will tie me to this application for the rest of my life (unless I want to retag thousands of files).  Any general advice you can offer on making universally acceptable tags that contain non-standard metadata will be greatly appreciated.

Thanks for your patience in reading all this, and for any advice you might have on any or all of these issues.  I feel a bit overwhelmed at the moment, and reluctant to begin tagging my collection until I get a bit more comfortable.

Dublin Ohio

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