[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [AVT] Re: VMR-WB RTP Payload and Storage Formats
Gino,
Thanks - this is a much more compelling explanation of the problem. The
issue with switching between sampling rates in an RTP session is a well
known problem with the way audio payload formats have been defined in
the RTP/AVP profile. If you want to work to solve that in the general
case, I would support that work. However, introducing workarounds for
specific codec - making it inconsistent with the others in the profile
- doesn't seem like a good idea to me.
On 5 Oct 2004, at 05:58, Scribano Gino-QA1087 wrote:
It seems that the 'sampling rate' issue has now crossed over to the
Storage Format thread. In any case, it's been a while since my initial
comments regarding application impacts of restricting the RTP
timestamp to be equivalent to the source media sampling rate. So, I
would like to reiterate that the impact of this restriction extends
well beyond saving a few bytes of storage in a tone generation box. As
I stated previously, this restriction is also problematic for mixing
and/or switching diverse media sources in streaming and conversational
applications.
Consider a conference bridging application, where at least one party
is a land-line circuit (which requires 8 KHz sampling) and at least
one other party is a wideband VMR-WB terminal (which may employ 16 KHz
sampling). Conference bridging for these media streams requires
switching and/or mixing the input streams into like output streams.
According to your restricted method, use of the VMR-WB sample rate
adaptation function for this application requires end-to-end session
renegotiation (eg, an SDP offer-answer cycle for each leg) in order to
achieve a common sampling rate, and hence timestamp interval, for all
RTP terminations involved in the conference bridge.
I would have thought the conference bridge could act as an RTP
translator, and resample as appropriate for some participants?
Additional latencies and synchronization complexities associated with
end-to-end renegotiation of the sampling rate for all RTP terminations
should not be required to establish and maintain the bridge in such
applications.
Colin
_______________________________________________
Audio/Video Transport Working Group
avt at ietf.org
https://www1.ietf.org/mailman/listinfo/avt