Help needed with maths (urgent)

[Colin Bignell]

'The two best CCTV images', *one* of which is only timed in minutes, and a distance of 350m between them suggest that there might be more than one source.

[Fredxx]

Or 24, or 30, or 50, or even 60. It rather depends on the format.

Cheap CCTV systems tend top be in the ad-hoc few frames per second, if you're lucky.

[GB]

Oh, right! No wonder we are at cross purposes. :)

Forgive me asking, but do these CCTV systems use an external time synchronisation source? Bill says they have the exact time, but if that depends on an internal clock, those could be out of sync by a minute or two.

[Steve Walker]

Hmmm, while the two systems won't be set to the same time, do they both use mains frequency to maintain their clocks? If so, the difference should remain constant, so record a clock on one and then the other and look where the two systems change from one minute to the next, to calculate the offset of one from the other?

[williamwright]

It's two separate cctv systems.

Bill

[williamwright]

Correct

[SH]

My cctv recorder uses the NTP protocol to get the time and date from a public timeserver...

handy for when there is a power cut so it grabs the time & date when power is restored or for when DST - GMT changes twice yearly.

S.

[williamwright]

They do tend to gain or lose a bit over a long period. The thing to do is as follows: As soon as you know that you need a timed recording check the time the machine displays and compare it with the correct time. Then add or subtract as appropriate to the time displayed on the recorded frames.

Bill

[Fredxx]

Some IP camera systems will use a NTP time server. I have one that does. That ought to have sub-second accuracy.

[Fredxx]

I have one on a UPS just in case a "smart" intruder turns off the power.