[vorbis-dev] Carrying non-audio data in an Ogg/Vorbis I stream

[Svante Seleborg]

Hello,

I would like to "piggy-back" other data in an Ogg/Vorbis I physical stream
(i.e. file) in a manner that does not conflict with specifications and
existing decoders/players/editors etc.

As far as I can see, I have some possible choices:

1 - Chaining a logical bistream at the end. If this is the way to go, two
questions arise to begin with:

q1a - How to identify this stream in a future-proof way? Just invent a new
header, beginning with 'm' 'y' 'h' 'e' 'a' 'd' 'e' 'r' ?

q1b - I have not found any specifications on how a decoder should handle
this - obviously I want a silent ignore, not an error message or even worse,
a failure to decode. Is this defined somewhere?

2 - Inserting non-audio packets in the actual stream. This situation is
defined to be decoded as 'a non-audio packet when audio is expected
indicates stream corruption or a non-compliant stream. The decoder must
ignore the packet and not attempt decoding it to audio.'. The second part of
this is ok for my purpose, but I don't like the sound of the first part
'indicates stream corruption' etc. An overly ambitiuos decoder might flag
this as an error for example.

3 - Another choice, which for various reasons feel less satisfying, is to
encode it as comments. The problem with this is first of all that it may be
attepmpted to be shown by decoders/players/editors, and second of all that
the data in question may be *large* (i.e. significantly larger than the
actual audio) - and it is unfortunate to have it at the front...

4 - Can I possibly just concatenate a completely separate Ogg stream at the
end of the first one? This seems to violate the constraints of an Ogg/Vorbis
I stream though.

In general, is there really no defined way to introduce data into an
Ogg/Vorbis I stream that is well-defined to be silently ignored by current
decoders, without this implying an error, non-compliance or whatever?

Ideas, comments - or just pointers to the appropriate specifications are
appreciated.

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