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Re: [AVT] Working group last call: JPEG-2000 payload format
Boudani Ali skrev:
2- In section 4.1 of Draft-ietf-avt-rtp-jpeg2000-15.txt: you consider 90
KHz for the Timestamp, this is not enough for professional video using
JPEG2K: isn't better to leave this to the implementers?
Can you please clarify why it isn't enough with a 90 kHz clock even for
professional video? When is their need for time jitter related to when a
frame was sampled needs to be smaller than what a 90kHz clock provide.
Especially considering that most of the frame rates used will have
perfect match to a particular tick increment per frame. I don't think we
have heard any such issues being raised in AVT before. If we do miss a
critical motivation then this applies to all our video payload formats,
not only one.
However unless there is strong motivation to change this I think staying
with 90kHz is a good choice. I know of least two reasons, both having to
do why you shouldn't leave this with the implementors.
1. First, if any timestamp rate can occur all receivers need to include
code that support any values. This makes implementations more complex.
2. The timestamp rate may not be set to low, as this will reduce the
utility of the RTCP receiver reports that uses the media codec timestamp
rate in its measurement. This has occurred for example for MPEG-4 which
allows flexible timestamp setting, when some senders used 30Hz as
timestamp rate. For RTCP sakes the timestamp rate should at least be 1kHz.
Therefore I think staying with 90kHz as one and only rate is better. But
please provide more motivation why pro-video will have issues with that.
Cheers
Magnus Westerlund
IETF Transport Area Director & TSVWG Chair
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Multimedia Technologies, Ericsson Research EAB/TVM/M
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Ericsson AB | Phone +46 8 4048287
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S-164 80 Stockholm, Sweden | mailto: magnus.westerlund at ericsson.com
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