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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