Vorbis - Jan 2002 - Ogg and Vorbis questions

>From the top of vorbisfile.c:
/* A 'chained bitstream' is a Vorbis bitstream that contains more than
   one logical bitstream arranged end to end (the only form of Ogg
   multiplexing allowed in a Vorbis bitstream; grouping [parallel
   multiplexing] is not allowed in Vorbis) */

Is this paragraph talking about multiple streams in a single Vorbis stream in an
Ogg, or is it talking about multiple Vorbis streams in a single Ogg?

(If it's the former while the latter remains possible, OggVorbis is really
awesome ::-)

And I can make an Ogg that has a Vorbis stream, and maybe a FLAC stream and
perhaps another FLAC stream in it, right?  (I'd look this up on the site,
but I
can't seem to reach it...)

Thanks,
        Ross Vandegrift
        ross@willow.seitz.com

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On Fri, 18 Jan 2002, Ross Vandegrift wrote:
> Is this paragraph talking about multiple streams in a single Vorbis stream
in an
> Ogg, or is it talking about multiple Vorbis streams in a single Ogg?
> 
> (If it's the former while the latter remains possible, OggVorbis is
really
> awesome ::-)
> 
> And I can make an Ogg that has a Vorbis stream, and maybe a FLAC stream and
> perhaps another FLAC stream in it, right?  (I'd look this up on the
site, but I
> can't seem to reach it...)
I think you might be confused about some terms.  Here is a one way to think
about it:

* The Ogg file taken as a whole (either on disk or streaming through your
network connection) is a _physical bitstream_.  In theory, a physical bistream
can contain data corresponding to all sorts of media types.

* The physical bitstream can be broken down into 1 or more _logical
bitstreams_.  Each logical bitstream contains data of a particular format,
like Vorbis, FLAC, Tarkin, etc.  Most Ogg file you run into are degenerate
streams which contain exactly one logical bitstream containing Vorbis data.

* Chaining refers to the property of Ogg files that two physical Ogg streams
concatenated together is also a valid physical Ogg stream.  The interpretation
of this is that the logical bitstreams in the second file are played after the
logical bitstreams in the first file.  This is handy for streaming where you
might output each file from your playlist, one after the other, in a
continuous stream.

But, yes, you can put two FLAC streams and a Vorbis stream into the same Ogg
physical stream, each in their own logical bitstream.


---
Stan Seibert

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