[xiph-rtp] About wkc

[Luca Barbato]

One of the remaining points to discuss is about static defined and well
known configurations. I doesn't make much sense supporting that for
vorbis and theora, but I got that request.

Current status of the section:

- Define it as an out of band delivery method as any other possible

- The uri provided tell where to fetch the full batch/list of
Configurations and a checksum is provided to validate it

- Start counting the Ident for wkc from 2^23 (or just use the odd ones,
depending on which endian you like more)

- you MUST always provide another way to fetch them (compatibility)

Pros:
- Doesn't alter anything in the currently defined structure

Cons:
- It has a fixed set of Idents reserved for wkc

Neutral consideration
- It will provide full configurations so it could even make LESS sense
- Someone could abuse/misuse it, degrading the quality of the encoded files.

Possible improvements

- Specify an optional offset for the Ident count for every Config
delivery method so that you can reserve just the right amount of Idents
for each use [keep in mind that everything is a special case of a
special case (chaining inside the same rtp session) and shouldn't be
used very often)]

- Redefine a bit the configuration format to
- Send Configurations w/out the codebooks
- have a Well known list of codebooks.

Those changes are relatively simple but I'm not so keen in adding
complexity for a feature that is hard to use properly and that got
already people against.

I hope to get some feedback about this issue.

lu