[xiph-rtp] Theora "setup idents" and codebook URLs in SDP

[David Barrett]

Phil Kerr wrote:
> Hi David,
> 
> David Barrett wrote:
> 
>> "A codebook URL SHOULD include a CRC32 of the codebook itself, so as 
>> to prevent the codebook referenced by URL from changing, and thereby 
>> enabling decoding clients to use the URL as a persistent, 
>> globally-unique identifier of the codebook itself, suitable for 
>> reliable caching purposes."
> 
> Yup.  But how do we prevent clashes with the packet ident?

In this proposal, there is no global uniqueness requirement for the 
"setup ident" field in each packet.  Rather, there is a much easier 
"session uniqueness" requirement.

Because the broadcaster writes the SDP *and* the packets, it is both the 
sole author and user of the namespace.  (i.e., it defines the "setup 
ident" namespace by associating codebook URLs with "setup idents" in the 
SDP, and then it stamps packets as it sends them to match.)  Clashes are 
therefore extremely easy to avoid.

-david