[ID3 Dev] ID3v2 Best Practices

[Glenn Someone]

Understood and thanks for your response.

 

What I am not understanding, and why I was writing the e-mail, is why my implementation is working fine if I do not change the size of the ID3v2 tag header upon rewriting a MP3 file, but does not work fine if I do change the size header.  The program uses the same process in both cases.  I have looked at the binary dump of what I am writing, and compared it with Id3v2 data that Winamp/WMP will honor and do not notice anything irregular.

 

This makes me think that either I am misunderstanding something in the standard, or my implementation is off in a way that I am not seeing upon studying the data (for almost two weeks now).  This is why points #2 and #3 were written in the original e-mail.  Is there something that can be used (somewhere) to validate whether ID3v2 is correct or not?  If not, would it be possible for someone to look at a bit of data and see what is wrong about it?
 
> Date: Sat, 25 Jul 2009 11:31:18 +0000
> From: mathiaskunter at yahoo.de
> To: id3v2 at id3.org
> Subject: Re: [ID3 Dev] ID3v2 Best Practices
> 
> 
> Regarding point 4):
> 
> From the specs (version 2.3.0):
> 
> >ID3v2 header
> >
> >The ID3v2 tag header, which should be the first information in the file, is 10 bytes as follows: [...]
> >
> >The ID3v2 tag size is the size of the complete tag after unsychronisation,
> >including padding, excluding the header but not excluding the extended
> >header (total tag size - 10).
> 
> This means:
> *tag* header size field = size of ID3 tag *data* (excluding the tag header size of 10 bytes).
> *tag* header size field + 10 = size of entire ID3 tag = offset in bytes of first MPEG frame (start of audio data).
> 
> >All the frames consists of a frame header. [...]
> >The size is calculated as frame size excluding frame header (frame size - 10).
> 
> This means:
> *frame* header size field = size of current frame *data* (including possible additional flag data, excluding the frame header size of 10 bytes).
> *frame* header size field + 10 = size of entire current frame (including possible additional flag data, including the frame header size of 10 bytes).
> 
> Hope it is clear now.
> 
> Regards,
> Mathias K.
> 
> 
> 
> ________________________________
> Von: Glenn Someone <ggrotz73 at hotmail.com>
> An: id3v2 at id3.org
> Gesendet: Samstag, den 25. Juli 2009, 11:23:43 Uhr
> Betreff: [ID3 Dev] ID3v2 Best Practices
> 
> A few questions that I have:
> 1) Obvious one is if this place is still active, since I have not received any e-mails from this list since I joined it....if it is...
> 
> 2) Is there a list of best practices on implementing ID3v2 anywhere, which describes all the possible nuances/problems that might be encountered between other implementations? For example, dealing with the wierd DWord format describing the structure size? Or some of the other stuff that seems to be unimplemented in most of the MP3 file examples I have. Or some of the v4 features (I started off the v3 documentation), that seem even more confusing...
> 3) For that matter, any good way to validate a tag structure? Like a program to show errors & deviations from the "standard"?
> 4) While I find much convoluted/confusing in the documentation on the website, the biggest one that I still have yet to resolve is this: I understood the size value (the wacky DWord) to be the size of the Frame Headers and Data to follow, but figured out after much time and failure in testing that it was the size of the data between the main header and the start of the MP3 data. 
> 
> Furthermore, I notice if I change this value (correctly, so that the MP3 data starts at the spot in question) upon rewriting the MP3 file that most other software (Winamp, WMP) will not honor the ID3v2 Frames. Upon playing with Winamp and adding much tag data, I found that it creates tag data based on KB boundaries. Is there a rule that states that this is so? Or is there some other likely error that I'm not catching upon studying the dump I am writing out of the ID3v2 data I have changed?
> 
> Anyway, I hope to hear back soon.
> 
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> 
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