[vorbis-dev] clarifications on comments spec

[Nathan I. Sharfi]

On Wed, 2 Jul 2003, Scott Wheeler wrote:

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> First, sorry that I'm slow on the responses -- my DSL provider doesn't love
> me.  ;-)
>
> On Monday 30 June 2003 13:17, Ralph Giles wrote:
> > Well, specification of the packet structure is *entirely* up to the
> > codec, so I wouldn't use Ogg::Comment. However, we do by convention use
> > this structure in our designs for speex, vorbis and theora. (I'm not
> > sure about Ogg FLAC) so maybe Xiph::Comment?
>
> Ok, I was forgetting that Ogg can contain non-Xiph formats.

FLAC is a Xiph format now, although we've been dragging on in the migration.
Do bear in mind that plain FLAC files are much more popular than Ogg FLAC
files, if only because liboggflac doesn't support seeking yet. Further, I
hear a number of hardware FLAC players don't handle Ogg FLAC for similar
reasons.

> > > *) Presuming there's no scheme for "padding" it would be nice if some
> > > convention could be adopted.  This makes "tagging" much faster since
> > > in most
> > > cases it won't require rewriting the entire file.  This could be as
> > > simple as
> > > a standard comment field with an obvious name -- but I think I've come
> > > up
> > > with a better solution; more on that later.

FLAC's solution is to add 4KB of a PADDING block right after the
VORBIS_COMMENT block. You'll be expected to handle that in this fashion;
however, you should have help through lib[ogg]flac[++].

> Given that Vorbis comments are text-only, I would assume that a limit of 64k
> really isn't a strange or unusual constraint -- I mean, printed, that's
> several full pages of text.  Certainly the "spirit" of the comment spec is
> that it's not meant for huge amounts of data (thinking of the comment that
> it's supposed to be equivalent to what you might jot on a CD-R).

FWIW, I've yet to go past 4K, even with my classical CDs.

Nathan
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