Hi everyone,
Yesterday I used the hackathon time to sync our modification with libwebrtc
57. I need now to sync chromium. Sergio is at the same point on his side.
Waiting for emil and boris to join the mailing list, I put those items here
for archive. Hopefully, they will join today (US time). Emil and I should
write the slides today for wednesday PERC session.
Sergio has some concerns with the OHB structure in our ICIP-submitted draft:
- On the original PERC IETF draft, the first bit of the PT is used to carry
the information of the X bit on the original RTP packet. In our draft, if
len =0,1,2 it should behave like the old draft, that is: the first bit
should still be the X bit. But if len>2, it then becomes a new "R" bit, the
meaning changes and the X bit is lost. We would not be able to signal the X
bit anymore.
- Moreover we cannot signal the M mark bit. this will be needed for SVC
streams if doing spatial layer selection
He'd like to propose a new format:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|M|X|P|S|Q|p| z |
+-+-+-+-+-+-+-+-+
M - mark bit
X - extension bit
P - Payload Type present (1 byte)
S - SSRC present (3 bytes)
Q - Seq Num present (2 bytes)
p - Padding present (1 byte)
z - zero fill padding (0,1 or 2 bytes)
This format has many improvements:
- it covers the missing info (extension, mark and padding bit)
- padding bit addition allows to support the empty bwe packets without
modification
- it has a easier parsing serialisation
- the zero fill padding is there to ensure len>2 to be backward compatible
with current draft
For discussion.
Alex, for sergio
--
Alex. Gouaillard, PhD, PhD, MBA
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President - CoSMo Software Consulting, Singapore
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sg.linkedin.com/agouaillard
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