[xiph-rtp] Lots of proposals

[David Barrett]

Tor-Einar Jarnbjo wrote:
> Are there really that many usage models for which
>  Vorbis over RTP is a feasible protocol?  ...
> I might have
> missed some of your opinions on this, but what are your concerns
> against HTTP and a separate RTP stream as not only the two mandatory
> delivery methods among several optional, but as the only two delivery
> methods defined?

Well, I don't claim to know all the uses, but in my case I'm using Speex 
and Theora (and eventually Vorbis) in a P2P scenario where peers are 
inaccessible via TCP because they're behind NATs and firewalls.  Thus:

1) HTTP is cumbersome because I'd need to have clients post their 
codebooks to a TCP-accessible server/peer, which undermines the value of 
a decentralized system and introduces greater points of failure.

2) A separate RTP stream brings no benefit as whether I send codebooks 
inline on the data RTP stream, or in a separate RTP stream, the 
broadcaster still has no idea if it ever arrives, and the receiver has 
no way of triggering a retransmit.  This leads to the wasted bandwidth 
and high setup latency that you spoke about earlier.

So in my case, neither of the two methods work well for me.  Yes, I can 
force them to work if they're the only options, but I'd prefer more 
options -- such as a "codebook ACK" packet sent via RTCP -- and I'd 
prefer to do it without breaking the standard.


> Is this problem really relevant for Speex? I am not 100% into the
> stream definition, but I was pretty sure that Speex does not require
> reliable delivery of any part of the stream.

Hm, I think you might be right -- Speex can make due with just what's
defined out of band, such as with SDP (which needs to be delivered 
reliably, but that's a separate concern).  Regardless, if the problem 
only exists for Vorbis and Theora (and possibly also Flac), and if the 
problem is identical for both, that seems sufficient justification for 
standardizing the solution between the two.


> Neither am I, but have you ever seen any software writing Ogg/Vorbis
>  files, which can not be read by any other software which supports 
> reading Ogg/Vorbis files? I think this is a very perfect analogy to
> RTP servers (producing Vorbis streams) and RTP clients (consuming
> Vorbis streams).

I agree, that's a good analogy, and I don't dispute the vision is 
compelling.  I just don't think it's practical given the differences 
between live RTP streams and standalone files.

-david