[LEAPSECS] Celebrating the new year a few seconds late

[Brooks Harris]

On 2019-01-01 9:36 AM, Philip Newton wrote:
> On Tue, 1 Jan 2019 at 15:33, Daniel R. Tobias <dan at tobias.name> wrote:
>> A lot of Americans synchronize their new year celebrations to the
>> drop of the ball in Times Square as seen on TV, which means they
>> celebrate a few seconds late because digital TV has an inherent delay
>> to it (for signal encoding or something... I really don't know the
>> technical details).
> You used to hear that during major sports events as well -- there'd be
> cheers coming up from various houses, then an echoing cheer a little
> bit later when those who had digital rather than analogue TV saw the
> goal.
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Back in the days of analog TV (which is still used in some parts of the 
world) the broadcast TV signal was one of the most stable time sources 
around. This was necessary because the display of the signal on a CRT TV 
set depended critically on the timing of the components of the signal, 
the horizontal and vertical scan lines of each frame (actually two 
interlaced 'fields').

There were experiments at NIST in the early days of TV to use the TV 
signal as a time dissemination source. It worked well, as coordinated 
with the NIST radio time signals. But it didn't turn out to be a 
practical solution.

All that real-time behavior went away with the advent of digital video 
and digital TV broadcast. Everything is buffered in some manner, 
sometimes very short, like parts of the picture scan lines, to entire 
frames, and, often many frames. There are many processes signals now 
propogate through, including compression and decompression of various 
formats, like Mpeg2, which is what we've mostly been watching for many 
years. New formats, including hi-def etc are constantly being adopted. 
With each of these stages there is some buffering and delay. And each 
facility and broadcaster has different equipment and procedures, so its 
unlikely any two TV signals are synchronous by the time they get to the 
audience's screens. And each TV set has its own internal buffering which 
adds more delay, and few of these products match each other in that 
respect. And, as noted, live broadcasts are often intentionally delayed. 
"Live" is not really live.

And then there is internet video streaming. In that case of course 
everything is buffered at many stages through the network and on your 
computer's desktop. If you've watched some live streamed event you might 
find it streamed from two or more servers. I've seen 10-20 second delays 
and more between two "live" streams. And of course there's no telling 
how much delay has occurred since the physical event in front of the camera.

-Brooks