[time-nuts] Measuring TV delays

[Magnus Danielson]

On 03/01/14 15:05, David J Taylor wrote:
> There seems to be a mis-perception that folk might estimate a fixed
> delay and somehow use the data as a source of time.  That was certainly
> never my thinking, but simply to observe the delays, and see what values
> might be obtained.  I've contributed one, rather uncertain, data point.
> It would be interesting to know whether there is any timing data in the
> various digital streams we get, either via terrestrial or via satellite
> sources.

There are several potential time-signals, but I would say it would be a 
bit hard to verify their traceability, which makes the exercise difficult.

The MPEG-2 Transport Stream have PID timestamps for every channel. 
However, there is really no good TAI/UTC traceability in them. Also, 
re-stamping is used to cover up for delay variations.

VITC might be present, and might provide local time, but for NTSC 
countries there is a frequency error only partly covered in the 
drop-frame compensation which causes a deviating display-time from 
actual local time.

Caption can also carry time, but there is no guarantee it has a sane source.

Cheers,
Magnus