[ID3 Dev] id3v2-3 extended header

[Clemens Hammerl]

hi

more questions inline...

Am 14.08.2007 um 18:10 schrieb 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

So the extended header size is variable in 2.3/4 and not constantly  
10 Bytesin size? Im just confused about the variable size of the header.

I will not implement extended headers im only interested in parsing  
the Text Information Frames, so i have to search for the beginning of  
the frames at position 10(Tag header) + extendedHeaderSize +  
SizeOfPadding. Am I right?

>
> 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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