[xiph-rtp] draft-ietf-avt-rtp-vorbis confusion

[Luca Barbato]

Remi Denis-Courmont wrote:
> De:	Luca Barbato <lu_zero at gentoo.org>
> 
>> the Identification and the Setup MUST be
>> packed as they are, while the comment
>> header MAY be replaced with a dummy
>> one.
> 
> Yeah - but what is a "dummy" comment header?
> This is not defined in the I-D nor the Vorbis spec.

The vorbis spec defines the minimal header accepted. A sender could put 
there a string like "Program - Version" or just "".

"an empty one" "a different one" "a smaller one" would sound better?

> And how does this translate into the "number of headers" field,
> that comes at the beginning of the packed configuration packet?
> This does not seem to be specified anywhere.
> Add to that, that the xiph-rtp Vorbis example code does not sout of date,
> recipe for IOP failure.

gstreamer and lscube have fully interoperable independent implementations.

>>> A possibly more serious problem
>>> concerns the 2-bytes length which is
>>> prepended to "packets". The text
>>> seems to imply that, in the case of a
>>> fragmented packet, the field is found
>>> once at the beginning of the first
>>> fragment, and encodes the whole
>>> (defragmented) packet length.
> 
>> Could you point me/us the exact line?
> 
> The first sections imply that each Vorbis packet is prepended with a 2 byte length.
> That would "intuitively" mean that the 2-byte length is part of the fragmented data
> (like the UDP length of a fragmented IPv4 packet).

I spent some time to disambiguate the use of packet/payload and any word 
that may refer to the rtp payload or a group of samples encoded in a 
vorbis frame and the people requesting that were happy in the end.

> You however indicate that EACH fragment contains a length field at its beginning.
> This is consistent with the fragmentation examples, but counter-intuitive and
> contradicts my understanding of the previous sections.

This has been discussed before...

lu

-- 

Luca Barbato
Gentoo Council Member
Gentoo/linux Gentoo/PPC
http://dev.gentoo.org/~lu_zero