[Vorbis-dev] Re: [ogg-dev] Peer review draft for the new

Ian Malone ibmalone at gmail.com
Tue Oct 2 01:51:25 PDT 2007

Martin Leese wrote:
> "Silvia Pfeiffer" <silviapfeiffer1 at gmail.com> wrote:
> ...
>> First though let me start a discussion on skeleton here, which is
>> fundamental to this rfc and for which I'd like to get more input from
>> everyone.
>> I think, "application/ogg" makes not much sense without having
>> skeleton inside the ogg file. Half the reason for having a generic,
>> free-ended encapsulation format is to have headers that can specify
>> what is within such that any decoder has a chance to assess whether it
>> will be able to do something sensible with it. So, I would like to
>> actually prescribe the use of skeleton in application/ogg files.

<snip: not for .spx, .ogg>

> I am an outsider here, but sometimes that helps.

> 1.  Ogg Skeleton should be as mandatory as
>     possible without breaking significant numbers
>     of existing files in the wild.
>     There are obviously loads of Ogg Vorbis out
>     there.  If there are only a few Ogg speex files
>     in the wild then they are better handled by a
>     tool to automatically convert.

I think the Speex thing is a detail.  However as .spx
and .ogg are legacy provisions my opinion is changing
.spx would be contrary to that.

> 2.  Following on from 1, a tool which inputs an
>     Ogg containier with one or more streams, and
>     outputs a new Ogg container with the same
>     streams plus an Ogg Skeleton stream stuffed
>     in front would be very helpful.  The tool could
>     also select and create the appropriate file
>     extension.

This is pretty easy to write using liboggz from svn
and Tahseen's skeleton creating functions (in his
vorbis-tools branch).  I just haven't found an
afternoon to do it yet.

> 3.  You can't discuss Ogg contents without also
>     discussing the minimum requirements for Ogg
>     players.  I would suggest it is time to bite the
>     bullet and specify that players must recognize
>     and decode an Ogg Skeleton stream if
>     present.
>     At the moment, Ogg Skeleton can break
>     existing players.  This has got to change if
>     Xiph is to move forward.  Existing player
>     developers will need support to do this, and
>     you will lose a few who can't/wont do it, but it
>     has to be done.  Discussion should be about
>     "when" and "how", not "if".

I've thought since the 'clean-break' realisation
occurred for application/ogg audio/ogg and video/ogg
that the things you and Silvia have suggested were
an implicit part of this change.  The only one I'd
raise an eyebrow at is players must decode Skeleton
rather than simply tolerate its presence; Particularly
since I'm not sure what the practical requirements
would be.  (And applications shouldn't---in the plain
English sense---trust the Skeleton header for security
reasons.  It can only be a guide.)




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