Re: [AVT] RE: Carrying SMPTE time-codes in RTP streams, discussion email

[lazzaro <lazzaro at eecs.berkeley.edu>]

[Magnus and Dave in discussion on SMPTE]

> > > A. Is it acceptable to get the update a bit late? Using RTCP can 
> > > easily result in that the time code update arrives up to a few 
> > > seconds late. However if some latency is acceptable, the RTCP 
> > > bandwidth and the usage of the AVPF profile can ensure that one 
> > > maintain a limit on the latency to send the update.
> >
> >
> >  I *think* so...
>
> This is an important point, so further feedback on this is crucial.

I think the right answer to the question is "depends on the app", and
separates into two questions:

A. For the app, is associating the wrong SMPTE code with the RTP
stream for a few seconds a disaster?

B. For the app, how much advance notice does it have of an upcoming
SMPTE change?

Apps where A="yes" and B="very little if any" are probably not going
to be happy with the RTCP approach ... apps where A="no" will be
fine with the RTCP approach ... the final class of apps is "it depends".

An example of "B=little if any" is when the SMPTE is changing because
an operator is hitting buttons on a tape-deck controller, and is 
expecting
the RTP-controlled rack-mount to respond with 5 ms latency over a local
LAN in a reliable way.

---
John Lazzaro
http://www.cs.berkeley.edu/~lazzaro
lazzaro [at] cs [dot] berkeley [dot] edu
---


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