[vorbis-dev] Xiph Magic

[Andrew MacLennan]

On Thu, 17 Jul 2003, Andrew MacLennan wrote:

> > >sure about Speex but I'm pretty sure that Vorbis packets are not
> > >self-sized.  If not, how come simply trimming (non-header) Vorbis
> > >packets is supposed to produce a legal Vorbis file?  Quoting the spec:
> > >"Vorbis provides none of its own framing, synchronization or
> > >protection against errors".
> >
> > In theory, it is possible to decode an incomplete Vorbis packet and
> > still render some sort of audio output. In a Vorbis packet, the order
> > of information is sorted according to importance, so if the last
> > part of a Vorbis packet is missing, the decoder could be (according
> > to the spec probably should be) able to produce audio output with
> > minial distortion.
> >
> > In the normal case (and I am quite sure, that the common players
> > would fail playing a properly Ogg-framed Vorbis stream with incomplete
> > packets), the packets are complete and the decoder is able to determine
> > the end of a packet without relying on the Ogg framing.
>
> 	I may be overlooking something very obvious (given that I haven't
> had too much chance to study the Vorbis spec. yet), but I don't see how
> Vorbis packets can be self-contained ie. in particular, how a decoder
> might determine the end-of-packet condition without higher-level framing ?
> Could you (or anyone) explain this a little more ?

        Actually having just read Beni's recent post, it's occurred to me
I didn't phrase my question very well : I meant to question whether Vorbis
packets are self-contained in the sense of being able to determine a
*premature* end-of-packet condition - I'm reasonably sure they're not ?
To be fair, I misread Tor-Einar's original comment : I understand that
Vorbis packets *are* self-contained if they're guaranteed valid and
uncorrupted.

Andy MacLennan.

--- >8 ----
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