[xiph-rtp] Ident field and configuration - stream mapping

[Ralph Giles]

On Fri, Oct 14, 2005 at 01:54:43AM +0200, Luca Barbato wrote:

> a stream radio wants to just use one single continuous rtp stream.
> 
> with 256 codebook possible the stream would last about 1280m ( 5min per 
> song, plausible) that means less than a day
> 
> take 65536 ,that means about 227 days
> 
> take 2^24 and you have enough years of music.
> 
> with 2^32 you have something more.
> 
> Let me just say that is an abusive behavior (better have different 
> sessions) and as usual are random numbers.

Yes, your summary is accurate. In practice the numbers for Vorbis
would be must better because there aren't that many different codebook
sets in use, and just tuning the huffman tables has been demonstrated
to offer too little optimization.

We expect both the number of setup switches and the chance of a CRC32
collision to be greater for Theora, since there are active plans to
develop and encoder that adapts the decoder setup to a particular
input set.

I'd decided that 16 bits was good enough, and just left the other 8 
reserved as a hedge against needs. We could use them to define 
a standard set of 'profile' codebooks, for example. What do you think
about that?
 
> Direct mapping will require to put a start value for the off band case 
> or another way to map them correctly. I'm thinking either of additional 
> fields or (ab)use the uri in a way similar to 
> proto://host.x/path/stream_id/codebook_number

Yes, Aaron suggested a very similar url contruction scheme to allow
new sets of headers to be posted and retrieved during live encoding.
I'm ok including this as a MAY in one of the out-of-band transfer
documents.

Speaking of, if you want to document retrieval over http separately,
could you write that up? I'd like to describe both it and the separate
multicast channel techniques asap because they're important for useful
implementation. We could also mention them in passing in the payload 
draft, which would give people the idea of what to do.

 -r