Re: [AVTCORE] [MMUSIC] BUNDLE: a single stream with multiple MIDs?

On Fri, Jul 8, 2016 at 4:06 AM, Jonathan Lennox <jonathan@vidyo.com> wrote:

> Hi, all —
>
> (This was an issue I raised in AVTCORE in Buenos Aires — I promised to
> send e-mail to the list but hadn’t remembered to get around to it until
> now.)
>
> When finishing up the CLUE RTP mapping draft, I realized that one of
> CLUE’s RTP requirements didn’t actually end up getting satisfied by BUNDLE
> (which is the solution CLUE converged on).  This isn’t a CLUE-specific
> issue, so I’m raising it here.
>
> The issue is whether we want to support a use case, in BUNDLE, where a
> single RTP stream corresponds to more than media description (and thus has
> more than one MID value)?
>
> The use case is where one m-line has a semantic of “always view this
> person” (my boss, say, or my customer); and another m-line has a semantic
> of “the current loudest speaker”. (In CLUE, these would be a single content
> capture in the former case, and a switched capture for the latter.)
> Whenever the boss *is* the current loudest speaker, the same content would
> be sent for both m-lines.
>
> A naive implementation would simply duplicate all the packets for the two
> m-lines, with different MID values, but this has two problems.  First off
> all, it obviously wastes bandwidth.  Potentially more seriously, it
> precludes any RTP middlebox topology which doesn’t rewrite SSRC values,
> since the same content (arriving with a single SSRC value at the middlebox)
> would need to be sent with two different SSRC values down from the
> middlebox.  If PERC goes with its current consensus of no SSRC rewriting,
> this will particularly be a problem for PERC.
>
> I certainly don’t think this is something that should block BUNDLE’s
> completion, but I think it could be a pretty easy extension.
>
> (My initial design proposal was to allow multiple SDES values of the same
> type, and multiple SDES header extensions items of the same type, to be
> sent simultaneously in RTP — protocol-syntactically this is trivial, you’d
> just need to negotiate that you support it.  But I’m not wedded to this
> solution.)
>
>
Thinking a bit more on this .. it seems like a nice way forward . I agree
with Magnus that it needs a way for the recipient to understand
addition/removal of an item from the set ..
If the set represent duplicates , then when the boss is the loud speaker,
the set will contain 2 mids .. when the loudest speaker is not the boss,
the set will have just one item in this example and the receiver will do
the normal processing of the loudest speaker .. From the mux point of view
these MIDs must be IDENTICAL-PER-PT

> What do people think — is this worth working on?  Is there interest in
> discussing it in Berlin, and if so, in what venue?
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