[ID3 Dev] User-Defined Frames

Jud White jwhite at cdtag.com
Sat Mar 3 18:43:23 PST 2007

1. Yes, text in TCON is compliant.  It's not defined as only a numeric 
2. The preferred way to delimit genres is with a null terminator, 
although only a few apps/libs support this.  There's no reason spaces 
should break another reader.
3. TIT1 might be good for "Theme", if your software writes this frame.  
The definition for TIT1: "The 'Content group description' frame is used 
if the sound belongs to a larger category of sounds/music. For example, 
classical music is often sorted in different musical sections (e.g. 
"Piano Concerto", "Weather - Hurricane").". If not, TXXX seems most 
appropriate, but you mentioned MM doesn't support these either.  Foobar 
definitely allows TXXX.  I would stay away from using COMM, because it's 
not a comment, although iTunes and other software abuse this frame 
4. It doesn't break the spec that MM writes its own COMM identifiers, 
but it is messy IMO.  I wouldn't worry about it breaking another app, 
but I would doubt another app would treat a MM COMM frame as anything 
other than a comment.
5. TXXX is appropriate if you want to define your own metadata.  A 
populer one is "Album Artist" for compilation CD's.  So you could have 
TXXX/Album Artist/DJ Dara, for example.  COMM is meant for comments, 
maybe some notes about a live recording, or a press release about a CD, etc.

If you use proprietary descriptors in COMM then you're righ to worry 
about lock-in.  You may be able to find someone willing to write a 
conversion utility to take COMM/MediaMonkey frames and translate them 
into whatever you're looking for in the future.

John Slane wrote:
> 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.
> jaslane64
> Dublin Ohio
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