[speex-dev] vorbiscomments in speexenc

Monty xiphmont at xiph.org
Wed May 5 13:58:21 PDT 2004

Hi Conrad, I was discussing this with Jean-Marc just now...

> 	1. it doesn't append a "framing bit" to the end of the
> 	comments packet. According to the Vorbis comment spec,
> 	an ERROR must be flagged when decoding such a packet.

The framing bit is an obsolete concept when also in the context of Ogg
framing although it is part of the spec.  It provides nothing Ogg
doesn't provide in a production environment (it crept in during the
day when Ogg framing wasn't yet solid and the Vorbis codec was using
additional framing paranoia.  I left it in the spec on the basis of
'can't hurt when not using with Ogg').

That said... Obsolete or not, Vorbis decoders do check for it.  Speex
decoders do not.

So it seems a simple case of 'include the bit and everyone's happy!',
but we end up with a case of 'the encoder must write this bit which
the decoder must not read.'  That's probably worst of it.

Oh, one silly thing... the Vorbis I bitpacker is LSbit first.  The
comment header is octet-aligned (the only header that is).  So what
you really end up doing is writing '0x01'.

> 	2. it explicitly allows comments which are not of the
> 	form name=value, and even provides a commandline option
> 	for adding them.

Basic agreement here. 

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