[ntp:hackers] Fwd: Video Frame Rate Ref Clock

Warner Losh imp at bsdimp.com
Thu Dec 13 23:48:41 UTC 2012


On Dec 13, 2012, at 4:29 PM, houston.jim at comcast.net wrote:

> 
> 
> ----- Forwarded Message -----
> From: "houston jim" <houston.jim at comcast.net>
> To: "Hal Murray" <hmurray at megapathdsl.net>
> Cc: hackers at lists.ntp.org, OnePV1D at gmail.com
> Sent: Thursday, December 13, 2012 6:22:08 PM
> Subject: Re: [ntp:hackers] Video Frame Rate Ref Clock
> 
>>> I am looking for a Ref Clock that uses video I/O card frame rate.
>>> Any idea if such a thing exists?
>> 
>>> Our broadcast equipment all have GPS accurate video frame rates and
>>> this so
>>> using the frame rate seem like a logical source clock for NTP.
>> 
>> You need time as well as a stable frequency.
>> 
>> Is there a timestamp in one of the refresh slots? I did a quick google
>> and didn't find anything.
> 
> Hi Everyone,
> 
> I expect that it would be a SMPTE timecode.  I found this mentioned on 
> Wikipedia.  Maybe Bart will describe the video standard being used and
> we can check what it supports.
> 
> I would be worried that the time code might have the time from when the
> video was created rather than the current time.

It generally does. And there's a few different time code fields and standards to worry about as well (time within the picture and time filmed at least). There's another field for the current time, but I don't know how extensively it is deployed outside of terrestrial analog video broadcasts.

Warner


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