[vorbis] xml stream formats

[robert at moon.eorbit.net]

On 11 Jul, Ralph Giles wrote:
> A parser could adjust it's tree based on the <?context ?> tags, realizing
> it missed scenes 25-26, for example. If encounters an actual error
> (unbalanced tags) it could just seek the next context statement and
> restart.
> 
> I agree this is pretty complicated. :(

Yup, and its likely to get more complicated as we adjust it to handle
cases we haven't considered yet.

>> I would suggest that any text interleaved with a stream be subject to a FEC with a
>> redundancy of two or so. There has to be a text sequence counter, and chunks
>> of text should only be output if the block can be completely recovered.
>> This would leave the "blocking problem" (i.e., what constitutes a usable
>> piece of code, text, etc.) to the user/programmer at a higher level.
> 
> Ogg already takes care of ordering and checksumming of the pages, so we'll
> know if we've lost something. I think error correction is overkill; being
> able to just drop the missing bits and continue is reasonable enough.

Agreed.

> How often do we expect to have dropouts? As I understand it, all mp3
> streaming happens over TCP where this isn't a problem, but that things
> like mbone video netcasts usually use UDP. Maybe Jack could comment here?

I hate nullsoft for taking the easy way out and only supporting TCP. UDP
is more suited for streaming protocols -- especially since you have the
choice between unicast and multicast. 

Packets get dropped pretty frequently -- any collision on the network
involving a streaming UDP packet will cause the UDP packet will get
lost. The protocol should abstract all that out for us and the codec
needs to be able to handle missing data in the data stream when the
protocol cannot recover lost data.

--ruaok         Freezerburn! All else is only icing. -- Soul Coughing

Robert Kaye -- robert at moon.eorbit.net  http://moon.eorbit.net/~robert

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