Re: [id3lib-devel] id3v2.4 tags

[David E. <eh...@gm...>]

David Ehrmann wrote:
> And a random question:
> 
> Why are there two 00 bytes following the description string (line 3)?
> 54 00 I understand; that's 'T.'  The next 00 is in the id3 specs and
> documented as a delimiter.  The third seems to indicate the character
> encoding, but 00 is ISO-8859-1, and the following string is clearly
> UTF-16 with BOM, like the first string.
> 
> 00000080   54 58 58 58  00 00 00 35  00 00 01 FF  FE 41 00 4C
> TXXX...5.....A.L
> 00000090   00 42 00 55  00 4D 00 41  00 52 00 54  00 49 00 53
> .B.U.M.A.R.T.I.S
> 000000A0   00 54 00 53  00 4F 00 52  00 54 00 00  00 FF FE 53
> .T.S.O.R.T.....S
> 000000B0   00 74 00 72  00 6F 00 6B  00 65 00 20  00 39 00 00
> .t.r.o.k.e. .9..
> 
> Changing the 00 preceding FF FE to 01 causes a parse error.  The
> description is printed by id3v2, but not the value.

I think I have my answer.

4.2.6.   User defined text information frame

    This frame is intended for one-string text information concerning the
    audio file in a similar way to the other "T"-frames. The frame body
    consists of a description of the string, represented as a terminated
    string, followed by the actual string. There may be more than one
    "TXXX" frame in each tag, but only one with the same description.

      <Header for 'User defined text information frame', ID: "TXXX">
      Text encoding     $xx
      Description       <text string according to encoding> $00 (00)
      Value             <text string according to encoding>


One 00 finishes the character started by 54, the other *two* terminate 
the string (but if this was UTF-8, one 00 would terminate the string).