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Re: [AVT] RE: [Sip] RE: [Sip-implementors] media description in SDP is for sender or receiver?
Hi Ling,
See inline.
Ling, Fan wrote:
Magnus,
You are dead on on the issues we are concerned about. Initially, our
understanding is the same as yours. However, when we proceed from
one-to-one video telephony application to multiparty video conference
application, the same understanding brings in some trouble.
Let's assume "MPEG4 simple profile level 1" is the negotiated codec.
In one-to-one video telephony, both ends can use different video sending
parameters, that is, "config=" or VOL parameters, both ends decoder just
configure itself to the incoming video bitstream's setting. In
multiparty conference, this means any one terminal has to configure its
multiple decoders according to different incoming bitstreams. This makes
the system a lot more complicated.
I don't see that you can avoid this. You anyway need to save the per
stream decoder state, thus all active participants will result in state
on the receiver side.
However isn't the real issue in multi-party that in many of the setup
scenarios you are not able to describe in the answer more than a single
configuration. Thus you are forced to use the inband transport that is
not as robust.
That's why we are coming back to the standards, to see whether there is
a rule that dictates that not only the codec type needs to be the same,
the video bitstream parameters (VOL) also needs to be the same for both
encoder and decoder.
To my knowledge this is not possible. However input from video coding
experts are solicited.
Cheers
Magnus Westerlund
Multimedia Technologies, Ericsson Research EAB/TVA/A
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