[xiph-rtp] header ident decision

[Phil Kerr]

Ralph Giles wrote:

>On Tue, Apr 05, 2005 at 08:28:29PM -0700, Ralph Giles wrote:
>
>  
>
>>Therefore I'd propose the following payload header:
>>
>>    0                   1                   2                   3
>>    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
>>   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>>   |           Setup Ident         |   Reserved    |C|F|R| # pkts. |
>>   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>>
>>    
>>
>
>Discussion on this point seems to have petered out. I'm going to decide 
>executively in favor of this proposal rather than Aaron's, with the 
>blessing of Fluendo. Phil, please (again) update the draft to reflect 
>this new payload header, and Aaron's changes to the meaning of the C,F 
>bits.
>  
>
Will do.

>Rationale for the record: Aaron's variable-length setup ident encoding 
>is much more flexible, but also adds complexity. While it's true that's 
>nothing compared actual vorbis or theora decode, the packetizer is not 
>necessarily an integral part of the decoder. I'm particularly worried 
>about the additional decision overhead for embedded use, where the fix 
>32 bit alignment makes things dead easy. It's also a stronger decision 
>against the 32 bit CRC proposal, preventing any kind of application-
>specific fallback. Finally, next to the 32 bit SRC id's and timestamp 
>in the RTP header itself, the 3 byte overhead for non-chained streams
>felt like a reasonable balance to me.
>
>So there we go, progress!
>
>  
>
Yippee!

>I've made no decision on the out-of-bound setup transmission issue 
>though. Storage formats, levels of indirection and so on are still up
>in the air. Really, I'd like to see some implementations try different
>things.
>  
>
This can be looked at later.

>One this I think we can define is in-band transmission. Just send the
>header packets in the RTP stream like they were any other type. The 
>16 bit setup ident field of the header packets must match the setup 
>ident of the data packets that rely on them. 
>
Do we care about setup ident collisions?

>In the default case the 
>three standard headers are sent at the beginning of the stream, just
>as they are in Ogg. The server MAY also retransmit the headers 
>periodically; clients MUST handle such header packets when they occur.
>  
>
This is catered for in the current documentation.

-P

> -r
>
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