Subject: Re: LATM specified in a public MPEG document?

From: John Lazzaro <[email-masked]>
Date: Fri, 22 Sep 2000 11:15:20 -0700

>> Simple SA session without scene description can be realized
>> by the LATM-based RTP specification.

> Are these facts already stated within the current LATM description?
>  We otherwise would now have the chance to clear these matters by means
> of the Corrigendum (deadline is the end of September).

Since there's no publicly-available LATM document, I'm on shakey ground
commenting on this, but nonetheless -- note that the MIDI
SA_access_unit's don't include their own timestamp (unlike SASL SA_access_units
that do have an optional timestamp in "scorebeats", which are tempo
modulatable), and since Bodo Teichmann's comment stated:

> [ Bodo Teichmann <[email-masked]> writes] 
> 
> > LATM was actually developed for only "natural"  audio coders, 
> > i.e. not fo Structured Audio. it is not possible to transmitt
> > multiple objects, no scene desctipion  and no time stamps
> > can be transmitted .

This means that taking LATM by itself, there would be no way to have
timestamps on MIDI SA_access_units.

For RTP over LATM this shouldn't be insurmountable, because of the RTP
timestamps, but if the Corrigendum you're mentioning isn't about LATM
over RTP but just LATM itself, it would seem to break using MIDI in
SA_access_units for all but "use immediately" semantics, which is 
what I assumed the quoted section above meant to convey.

For my own work, its becoming clear that making an RTP packetization
just for Structured Audio is the right thing to do -- one lost MIDI
NoteOff command can really wreck the entire performance (for those   
not familiar with MIDI, NoteOff's end individual notes of a performance
which are begun by a NoteOn -- a lost NoteOff means a note that sounds
"forever"), and a packetization meant for interactive performance over
low-latency networks really has to address this issue to be useful,
either by schemes similiar to draft-ietf-avt-rtprx-00.txt for unicast,
or by various FEC approaches for multicast ...

-------------------------------------------------------------------------
John Lazzaro -- Research Specialist -- CS Division -- EECS -- UC Berkeley
lazzaro [at] cs [dot] berkeley [dot] edu     www.cs.berkeley.edu/~lazzaro
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From: Dave Singer <[email-masked]>
Date: Fri, 22 Sep 2000 11:35:40 -0700

At 11:15 AM -0700 9/22/00, John Lazzaro wrote:
>Since there's no publicly-available LATM document,

well, this is a show-stopper.  we cannot base a standard on something 
that is not publicly defined.
-- 
David Singer
Apple Computer/QuickTime