Subject: [AVT] MWPP and the marker bit ...

From: John Lazzaro <[email-masked]>
Date: Thu, 3 Apr 2003 10:29:20 -0800

Hi everyone,

	Looking for input on the following MWPP issue ...

From the draft-ietf-avt-mpeg4-simple-07.txt:

   Marker (M) bit: The M bit is set to 1 to indicate that the RTP 
   packet payload contains either the final fragment of a fragmented 
   Access Unit or one or more complete Access Units.

MWPP needs 1-packet-per-access-unit semantics to work properly, and so
MWPP defines the M bit to always 1 for mpeg4-generic use.

Up until now, I've also defined the M bit to always be 1 for "native
MWPP streams" (mwpp MIME type), on the theory the confusion that would
come from having two different M bit uses for the different MIME types
outweighs the advantage of using the M bit for something useful.

However, the recent discussion on the list over voice-codec M bit use
has made me wonder if I should instead define the M bit for the mwpp
MIME type to have a meaning akin to the voice-spurt M bit meaning.
For mwpp, this semantic would be "any packet that codes at least one
new MIDI command", and the purpose would be to let receivers quickly
distinguish empty "guard packets" from packets with new data.

Any input one way or the other is appreciated -- I'm undecided at this
point ...

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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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