Vorbis dev - Oct 2003 - Detecting packet lengths in Vorbis-streams

How would one implement the following scheme with minimal use of
resources:

Every Vorbis packet should be preprocessed to a certain extent, that is,
the beginning of every audio packet should be parsed and some decoding
steps executed. The result of this predecode as well as the rest of the
packet should then be sent as output for final processing.

I have skimmed through the standard, and as far as i can tell there is no
field containing the packet length, however the
'end-of-packet'-condition
is mentioned at severeal places, and it is also checked for at various
places in the decoder source code.

I would really appreciate an explanation of how the end-of-packet
condition is detected or any other suggestion on how to solve my problem.

Regards,
Erik

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Quoting Erik Montnemery <erik@babes-inc.com>: 
 
> How would one implement the following scheme with minimal use of 
> resources: 
>  
> Every Vorbis packet should be preprocessed to a certain extent, that is, 
> the beginning of every audio packet should be parsed and some decoding 
> steps executed. The result of this predecode as well as the rest of the 
> packet should then be sent as output for final processing. 
>  
> I have skimmed through the standard, and as far as i can tell there is no 
> field containing the packet length, however the
'end-of-packet'-condition
> is mentioned at severeal places, and it is also checked for at various 
> places in the decoder source code. 
 
The packet lengths are read from the "lacing values" at the end of Ogg
page
headers.  (Also referred to as the "segment_table" in the RFC.) 
 
http://www.ietf.org/rfc/rfc3533.txt 
 
Each Ogg page contains a set of packets, which in the case of a "degenerate
Vorbis stream" (i.e. a normal Ogg Vorbis file) will all be Vorbis packets. 
 
-Scott 
 
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