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[AVT] RTP streaming and adaptation to AVC of an SVC temporal scalable bitstream - Packet loss
Dear
all,
I'd like to clarify the following scenario
(the reference documents are draft-ietf-avt-rtp-svc-02.txt and
RFC-3984).
We're implementing a system
including:
a) an SVC encoder + RTP streamer module
(non-interleaved mode),
b) an SVCtoAVC adapter, taking the RTP
stream from the network, adapting its SVC payload to AVC, streaming (RTP)
the resulting AVC stream,
c) an RTP receiver + AVC
decoder.
The SVC encoder implements just temporal
scalability: it produces/sends AVC-compliant NALUs and before any of them a
prefix NALU to carry scalability information.
The different (temporal) layers are
transported in a single RTP session.
Let's suppose that the SVCtoAVC adapter has
to forward just the base layer by dropping the enhancement layers and the
prefix NALUs and making just some minor adaptation in the Sequence Parameter
Set.
Now the question: how can we handle a
packet loss in the path between the SVC encoder and the SVCtoAVC adapter,
considering the single RTP session?
The problem is that the SVCtoAVC adapter
is not able to know which layer the lost packet belongs to; it can just
detect a generic packet loss, which could affect either the base layer or an
enhancement layer, then the SVCtoAVC adapter doesn't know whether this loss
has to be signaled to the receiver, i.e. whether it must insert a
sequence number gap in the outcoming RTP stream...
If we used different RTP sessions the
hardle would be cleared, as the sequence number would be increased
separately for any layer. Anyway, we'd need to keep the single RTP session mode
(if allowed, of course).
Any suggestion would be very
appreciated.
Thanks in advance.
Best regards,
_______________________________________________
Audio/Video Transport Working Group
avt at ietf.org
https://www1.ietf.org/mailman/listinfo/avt