On 2019-01-01 9:36 AM, Philip Newton wrote:
On Tue, 1 Jan 2019 at 15:33, Daniel R. Tobias <[email protected]> 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.
_______________________________________________
LEAPSECS mailing list
[email protected]
https://pairlist6.pair.net/mailman/listinfo/leapsecs
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
_______________________________________________
LEAPSECS mailing list
[email protected]
https://pairlist6.pair.net/mailman/listinfo/leapsecs
