[ID3 Dev] User-Defined Frames

John Slane jaslane64 at yahoo.com
Sun Mar 4 09:00:42 PST 2007

Thanks very much for your kind reply.  Your perspective is very helpful to me, since my experience in this area is very limited.  Your suggestions will hopefully help me avoid making poor judgments that will come back to bite me later.

I know it was a long list of questions, and I appreciate your patience in addressing them all.

I am very grateful.

Jud White <jwhite at cdtag.com> wrote: 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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