[time-nuts] New Years Eve TV countdown
cfharris at erols.com
Thu Jan 1 23:21:27 EST 2015
I strongly suspect that the major cause of time lag in TV programs
seen on Digital over-the-air TV is in the TV sets themselves.
My evidence for this is observation of simulcast programs that are
broadcast in both HD and LD on different channels of the same
station. The HD always lags the LD by about 10 seconds on my
2014 vintage Sony TV. It was the same on my 2007 vintage Sony TV,
only maybe a little more so.
If it ever even once went the other way, I would consider that it
might be some anomaly at the broadcast station, but it never does...
So, I believe it is related to the processing effort the TV set has
to do to process HD over that of LD.
The stations can do all the work in the world to minimize their
time lags, and perhaps even achieve the 750ms you quote, and it will
all be for naught come New Years eve when some time nut notices
how the ball drops 8 or 10 seconds after the midnight we measure
through other means.
Simultaneous was possible in the days of analog TV to within 1 frame
plus transport time. Digital TV's are going to have to run a lot
faster than they do now just to catch up with what was routine in
Magnus Danielson wrote:
> In digital times, the main reason for creating delays is due to the temporal
> compression of MPEG-2 and MPEG-4. Production quality is either not compressed or
> JPEG-2000 compressed. If you do not compress at all, delay structure can be similar
> to that of analog video days. JPEG-2000 typically requires the full frame to be
> grabbed before serious crunching can be done, due to the 2D wavelet processing. There
> exists low-delay compression schemes which is in the handful of lines (about 16) of
> delay. MPEG-2 requires a re-arraning of transmission order in order for the
> IBBBPBBBP... sequence requires the I (or preceeding P) and following P be sent before
> the B frames interpolating between them.
> Add that many buffer management systems is horrible, especially when going over IP.
> Doing long distance (22500 km) 4K uncompressed video has been done with only 750 ms
> delay. That delay is probably trimable if you really need to.
> The one feature you have with digital video, is that you can create delays by mistake
> so easy, and that is gravely misused feature to this day. Let's say that most systems
> does not impress me.
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