On Feb 24, 2005, at 12:47 AM, Dave Singer wrote:
At 1:49 PM -0800 2/23/05, lazzaro wrote: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.
Note that the mapping itself in the RTCP can always be right; it's merely a question of whether it arrives too late for the terminal to be able to apply it to the media from the identified timestamp. If indeed the client wants a short buffer, and the source gets no advance notice, and it's not possible to send immediate RTCP packets, there may be an issue.
Agreed, in my description I was analyzing the actions the receiver takes if it needs to make a time stamp decision under time pressure, not the accuracy of the RTCP packet once it arrives.
--- John Lazzaro http://www.cs.berkeley.edu/~lazzaro lazzaro [at] cs [dot] berkeley [dot] edu ---
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