[vorbis-dev] Return of the Son of MIME type

[Ralph Giles]

On 27 Oct 2000, Maciej Stachowiak wrote:

> One thing I'd like to suggest is that your proposed TOC if any, list
> an intended primary purpose for the file in addition to a list of
> contained stream types (audio, video, other) to address issues others
> have raised about how it might not be possible to tell the purpose of
> a file just by looking at the list of stream types.

Monty and I discussed this a bit today; I thought I'd post a progress
summary.

We've both found the arguments you (Maciej and Rakholh) have made
convincing, but it remains to develop a technical solution. We've always
(well, as long as I've been around :) planned on having some kind of
stream description metadata for when we've got more than one substream.
Because of the way the ogg bitstream format is stuctured, the only place
this can go is in another logical substream. Adding a tag like you suggest
will be simple enough.

What's not clear is how to arrange for this to be efficiently testable. As
I said before, the only way I can see mime-magic working is to key on the
filename extension, or to guarantee that the first substream will be a
special-purpose, binary table effectively adding a header to the
headerless ogg. We're not really willing to do either of those.

That's about as far as we got. I've definitely added efficient
type-determination the the requirements for the metadata header, but
unless someone has a brilliant idea, a limited substring search will
probably be required. :-/

We still wish you wouldn't fork the mimetype, if only because we don't
know how we're going to do this yet. The only ogg files we're generating
now are "degenerate" in that they contain only a single vorbis substream.
However, since "efficient type determination" almost certainly means
putting the stream description metadata substrem (whew!) first, looking
for 'vorbis' at byte 29 like I initially suggested is probably not
the best idea. Associating application/x-ogg with the initial 'OggS', and
handing that to ogg123 by default strikes me as the most future-proof.

FWIW,
 -ralph


--
giles at ashlu.bc.ca

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