[ID3 Dev] id3v2-3 extended header

[Jim]

Hi Clemens.

I'm not sure which version of ID3v2 you are asking about.  However, in 
both v2.3 and v2.4 tags, the extended header size is the first four 
bytes.  For v2.3:

      Extended header size   $xx xx xx xx
      Extended Flags         $xx xx
      Size of padding        $xx xx xx xx

And for v2.4:

      Extended header size   4 * %0xxxxxxx
      Number of flag bytes       $01
      Extended Flags             $xx


Is that what you were asking?  (Both of those descriptions were taken 
from the specs available on the ID3 website so you can look there for a 
more thorough description of each field.)

I can only guess why the size is stored as 4 bytes.  My guesses would be 
both for future compatability if the extended header becomes larger in 
later versions and to make it standard with the rest of the sizes 
(overall tag size & frame sizes).

Jim


Clemens Hammerl wrote:
> Hi
> 
> Im new to id3 an this list and i'm currently working on an 
> implementation of ID3 for Java.
> I dont understand how the length of extended header is calculated. In 
> the specification stands that:
> 
> "...Where the 'Extended header size', currently 6 or 10 bytes, excludes
>    itself..."
> 
> But were in the header is the size of the header stored. Is it in the 
> first 4 bytes. Why do you use 4 bytes when the maximum length is 10B?
> 
> best regards clemens
> 
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