[vorbis] What tags are allowed in ogg files?

[Anders Thomsen]

Hi,

I'm writing a tag-editor for ogg files.
What tags, besides ogg-tags, are allowed in ogg files (if any).
I'm thinking of id3v1, id3v2, ape tags and so on.

I have a (probably small) problem with writing a new "comment header". I
have tried opening a file with a valid header, and then simply moved some of
the comment tags position,
so that the total size and the count still remains the same. I then save the
file and try to analyze it with the OggInfo tool, but it tells me:
"Warning: Could not decode vorbis header packet - invalid vorbis stream (1)"

If I analyze the two files with hexeditors, the contents are exactly the
same, except that two comment tags (and their leading 32 bit integer
describing the tags length) are switched position.

To write the file, i do this:

Bit-by-bit copying all contents of the existing file, until the beginning of
the "Vendor length" integer.
Then I write:
vendorlength (32 bit unsig. int)
vendorstring
comment count (32 bit unsig. int)
comment1 length) 32 bit unsig. int)
comment1 string (fieldname=value)
comment2 length..
..
..
and then I copy the rest of the contents from the existing file.

I've uploaded two sliced ogg files (200 kb each):
http://www.mexp.dk/ogg/test1.ogg    (this is the one I modified, so it
doesn't work)
http://www.mexp.dk/ogg/test2.ogg    (this is the original one, which is
okay)

I hope that a kind soul would care to explain to me what I'm doing wrong,
since I've been fiddling with this for two days (or rather nights), and
I've allmost pulled out every single hair on my head by now...

Thanks in advantage,

Regards,
Anders Thomsen

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