[AVT] Carrying SMPTE TimeCode in RTP

[Dave Singer <singer at apple.com>]

Answering my own email here, I'm assuming that the answer is yes to 
the 2nd question.

The extra bits in an 8-byte SMPTE time-code can be used to
a) maintain the polarity of the code (numbers of 1s and 0s)
b) indicate the relationship of the codes to color fields
c) indicate whether it's drop-frame coding
d) and then do one of
   i) carry 4 characters more
   ii) carry a date and time-zone indication (SMPTE 309M)
   iii) carry some general SMPTE 262M data (control codes, text, 
production info etc.)

I don't believe we need color and polarity handling in RTP.
We have drop-frame in the signalling.

If we want to carry something as slowly-changing as a date or as 
unchanging as a time-zone, I on't believe that embedding it here is 
right.  Certainly thought should be applied before blindly applying 
it.  If a date is needed, it's not needed inline;  at most it would 
be in RTCP, and then I would argue for a new RTCP packet type to 
carry it.

The other two possibilities are 'general meta-data' and should not be 
sub-embedded in a time-code, in RTP, but elevated and properly 
labelled at the stream level.

So, my answer is no, we do not need the full 8-byte SMPTE time-code.

On the other open question, it's a question of taste.  I prefer it 
this way but I'm not pedantic.



At 11:13  -0800 22/02/06, Dave Singer wrote:
> In this I-D, there are still a couple of open questions.  I'm 
> wondering if any on the list can indicate their preferences, or 
> whether the editor should make his best guess.
>
> Would people like more background info (e.g. the 6 flag bits and 8 
> 4-bit binary groups documentation)?
>
> * * * * *
>
>
> Open question: should we normally compute framespersecond from frameduration?
>
> Open question: should we allow for a full 8-byte SMPTE time-code 
> formatted exactly as in SMPTE 12M? We are currently missing the 6 
> flag bits and the 8 4-bit binary groups.
>
> --
> David Singer
> Apple Computer/QuickTime
>
> _______________________________________________
> Audio/Video Transport Working Group
> avt at ietf.org
> https://www1.ietf.org/mailman/listinfo/avt


--
David Singer
Apple Computer/QuickTime

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