Subject: [AVT] Take two: MWPP and the marker bit

From: John Lazzaro <[email-masked]>
Date: Thu, 3 Apr 2003 10:49:40 -0800

Hi everyone,

	Looks like my mailer truncated the posting I just sent to the
list, let's try again ...

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Hi everyone,

	Looking for input on the following MWPP issue ...

	MWPP supports two MIME types: mpeg4-generic for MPEG work
and mwpp for general use. From 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 "one access unit per packet" semantics for
the recovery journal to work, as so for mpeg4-generic use M
is defined to 1 for all packets.

	Currently, M is also defined to 1 for all packets for
use with the mwpp MIME type, on the theory that the confusion
that would result from two separate M bit definitions is best
avoided.

	However, reading over the recent list discussion on
voice codec marker bit use, I'm wondering if I should reverse
this decision, and define M bit semantics for the mwpp MIME type
that are in the spirit of voice-codec use (for MWPP, the right
definition is to use the M bit to differentiate packets with
new MIDI data from empty "guard" packets).

	Any input on this decision is appreciated, I'm undecided
at the 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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