Forwarded for Peter Vince.
Bill
-----Original Message-----
From: owner-s22-12m at eng.smpte.org on behalf of Peter Vince
Sent: Thu 3/2/2006 2:13 PM
To: s22-12m at eng.smpte.org
Cc:
Subject: (s22-12m) RE: (s22-list) FW: [AVT] Carrying SMPTE TimeCode
in RTP
I would argue that the date IS needed. Time code is highly
redundant, with the full HH:MM:SS:FF time being encoded every
frame. By this means, the full time can be decoded from even a
single frame. 24-hour broadcasting has been the norm for a long
time now, and therefore larger units of time than in the time part
of the time code are needed to ensure a contiguous and unambiguous
sequence. Further, to regenerate the original time code at the
other end, all the data needs to be carried.
Peter Vince (Snr.Engr., BBC TV, London)
Addr: Room 3057, BBC TV Centre, Wood Lane, Shepherd's Bush, London,
W12 7RJ
Tel.: +44-20-8576-0000
Fax.: +44-20-8576-0018
email: peter.vince.01 at bbc.co.uk
-----Original Message-----
From: owner-s22-list at eng.smpte.org [mailto:owner-s22-
list at eng.smpte.org] On Behalf Of Miller, William C
Sent: 02 March 2006 18:02
To: s22-list at eng.smpte.org
Subject: (s22-list) FW: [AVT] Carrying SMPTE TimeCode in RTP
Anyone want to comment?
Bill
-----Original Message-----
From: avt-bounces at ietf.org on behalf of Colin Perkins
Sent: Thu 3/2/2006 12:23 PM
To: Dave Singer
Cc: avt at ietf.org
Subject: Re: [AVT] Carrying SMPTE TimeCode in RTP
On 2 Mar 2006, at 00:42, Dave Singer wrote:
> 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.
Seems reasonable.
Colin
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