[ID3 Dev] Clarifying the TCON Frame

[Ben Bennett]

On Tue, Mar 06, 2007 at 05:42:23AM -0800, John Slane wrote:
...
> The various music-management software I am using (MediaMonkey,
> Mp3tag, etc.) are writing alphanumeric (English words) data to this
> type (Genre) frame.  So I would like to clarify a few things.
> 
> (1) Is a TCON frame really supposed to contain a numeric string?  If
> so, what is the definition of a "numeric string"?  


The 2.3 version of TCON is a mess.  2.4 made some changes, but it is
still a bit tricky.

It should not contain just a numeric string.

The format is optional parenthesized genre reference e.g.: (4)
Then an optional textual refinement e.g.: Eurodisco

There can be multiple references in the frame, and there are rules for
escaping (s.  There is no mention of multiple refinements, I would
assume only one, and at the end of the string.

You can also make references to RX for remix and CR for cover.
 
So these are legal strings:
 (4)
 (4)Euro Disco
 Euro Disco
 (21)(4)(RX)Euro Disco


> (2) If I have English words in a TCON frame
> e.g. TCON = Soul R&B Motown
> will that cause a problem with any apps down the road?

I think that is the safest and sanest thing to do.  I would not use
the references stuff.  iTunes puts just bare text in the frame and
does not handle lists.  And since iTunes is widely used, I would
assume other software tries to read their tags.


> (3) If alphanumeric words are allowed, what is the best way to
> delimit multiple values in the frame?  Are there any characters -
> delimiters or otherwise - that should be avoided in a TCON frame?

I do not think you can... the frame can not be repeated, and there is
no identification of a list separator in that frame.  The only
possible thing would be to do:
 (4)Euro Disco(32)Duck Themed

But I bet that is not well supported.

However, you can indicate multiple genres through textual convention:
  Euro Disco; Duck Theme
  Euro Disco -- Duck Theme
  Euro Disco / Duck Theme

Just pick what you think is most visually correct.

2.4 has proviisions for multiple values (using NUL as a separator).
But I think most software just shows the first value and ignores the
rest.


> So far, I have experimented with simply adding the multiple genres
> as a text string delimited only with spaces (as in the earlier
> example).  This seems to work OK for now, since I typically am
> searching for files with TCON containing a certain substring.  Is
> this a robust use of the TCON frame?  Are there rules/guidelines for
> entering multiple values into a Text Information Frame?  

Discussed above.


> One other question (which will show off what a newbie I am):
> 
> What is the essential difference(s) between Text Information Frames
> (TALB, TBPM, ...) and Comments Frames.  As best I can tell, a Text
> Information Frame is to contain a single string of text, with no
> carriage returns allowed.  A Comments Frame can contain carriage
> returns (newlines).  Is that the essential difference?

Not quite... the T*** frames indeed can only contain a single text
string with no newlines, but COMM is more general than that.  It is
basically a way for people (or programs) to stick arbittrary data into
the tag.  iTunes uses COMM for their audio normalization flag among
other things.

I would not expect COMMs to show up in various programs
consistently...  But yes, the "actual text" field can contain
newlines.


>  Also, is the USLT (Lyrics) frame type basically the same as a COMM
> frame, but simply with a specific purpose?

Yes.

			-ben

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