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

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

On Feb 13, 2005, at 4:06 PM, Dave Singer wrote:
> here is the draft.

Looks good, I never realized:

>    It is worth noting that in neither case is the SMPTE time-code an
>    accurate clock;  in the first case, it runs slow, and in the second,
>    the adjustments are abrupt and periodic - and still not quite
>    accurate.

Abrupt and periodic are both OK, but if over long periods of time,
if there's going to be a systematic slip of the RTP time base relative
to the SMPTE time base in the case of NTSC ... I could imagine that
being a problem in some applications.

Is there a standardized way to do a second-order adjustment
on top of the drop-frame adjustment, to make the timing perfect over
long periods of time?  Or is the standard method to make "nominal"
"real-time" conform to SMPTE time, sort of how we drop a second
or add a second from "official time" on New Years Eve every few years?

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


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