At the station that I worked at, time code was recorded in the
digital video stream in the camera, but, was only used for editing.
The editors would use this time code to mark the segment end points.
There was no correlation to the camera time code and actual time.
When we taped a show from a feed, we used internally generated time code.
This was used for the automation equipment.
If a recording had time code of 2359 - 0000 in the show, the show had
to be redubbed with time code that did not cross the day boundary.
Our automation equipment did not understand day nor did it understand
negative time.
I would guess that if the station were 100% automated, everything
that was broadcast would have valid time code.
We broadcast Network, prerecorded syndicated shows, commercials,
promos and locally produced programming.
Because of the in field switching between cameras and graphic sources
for a live broadcast camera time code was not important as the
switching was done manually (you cannot automate a live event).
There was probably continuos time code inserted at the output of the
production switcher, but,this time code was not used at our station
as we had to manually switch to a local source for promos,
commercial, and locally prepared programming.
I do not think that there would be a reason to preserve the camera
time code from camera to air.
I cannot see where it would be of much value as the camera would free
run time code.
It could be preset, but, there was nothing to guarantee frame
accuracy for the length of a live event that was shot with numerous
field cameras.
The cameras were gen locked to allowing glitch free switching between
sources at the production board, but, there is no way, that I know
of, to sync time code.
This is how the station that I worked at operated.
Other stations my have operated differently.
The bottom line is I know of no way to derive accurate time from a
present day TV signal without the station inserting time information
in the stream.
This is how the VCR time auto set worked.
But the uncertainties in the coding and decoding times would make
this less accurate than time derived from other available sources.
73
Glenn
WB4UIV
At 08:24 AM 1/3/2014, you wrote:
On 03/01/14 10:04, David J Taylor wrote:
From: Chris Albertson
When they broadcast "live" TV like from a sports vent I wonder if the time
code generated by the camera is preserved? But then even if it were the
time might have been set manually to match the display on the camera
operator's cell phone.
Same for scenes with clacks in the background. Do you trust them to be
on-time? They might even have ben intentionally set wrong to hide the
transmit delay.
=================================
Can't comment on the camera time-code, Chris, but I would hope it was
centralised rather than being off the operator's phone!
You try to lock up cameras with a "genlock" or "black-burst" signal,
which is a black signal with color-burst, and often VITC to get
production-time. Production time may be similar to local time. For
most live events I expect it to be, as it is very handy. Timing
generators can either be set manually or get time from GPS or such.
The reason to lock cameras up is that you don't need frame-stores to
align them up but can use the video-mixers line-stores instead. In
the old analog days, all delays in a studio was aligned up so that
the signalas matched to within 20 ns. This meant long cable-runs to
cable-equalize all cameras.
The clocks I mentioned, F1 races, do appear to be accurate (observations
partially from being present at the event), and certainly /not/ skewed
to compensate for broadcast delay. Other times are when you see "behind
the scenes" and a control-room clock is visible. Usually these are
centrally synced, and can give a fair impression of the broadcast delays.
Since you don't know the distribution and de-coding and trans-coding
delays, it's hopeless to come up with a skewed time to fit all.
Forget it. The mode is rather to live with the delay there is.
Cheers,
Magnus
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