> I build a video switcher between 2-3 cameras. my problem is
> when each camera is switched the picture is not stable, there's
> a "flick" on the monitor.  after 0.5 sec it become stable.  can
> I prevent this behavior? how can I make the switching "smoother"?

The problem, as many people have said, is that the video signals
from the multiple cameras are not phase locked (or genlocked).

Each camera has reasonably stable horizontal and vertical
oscilators for its internal use.  Each camera expects any monitor
to synchronize with that camera's video output signal.  After you
switch, the monitor skews its oscilators and resync to the "new"
video signal in about 1/2 second.

One major stumbling block is probably the type of cameras that
you are using.  Most inexpensive cameras do NOT provide a way to
feed an externally generated sync signal into the camera.
Therefore, multiple cameras of this type cannot be genlocked.

If all your cameras can accept external sync signals, then you
can get (or build) a master sync generator and distribute its
signal to all of your cameras.  This is how a multiple-camera
video/TV studio works.  And allows seamless cuts and fades from
one camera signal to another camera signal.

If you happen to have a set of N cameras where (N-1) will accept
external sync and 1 won't, you can make that 1 camera the master.
The video signal from the one camera that can't do external sync
becomes master.  You can buy (or make) a circuit to extract the
sync signals from its video output and feed them to the others.
But I expect this scenario is unlikely.

Resynchronizing 3 video signals -- after the fact -- to each
other is difficult & expensive.  The circuitry for each of (N-1)
video signals has to be able to time shift its signal one full
frame time to guarantee that it can remain sync'ed to the master.

                                                Lee Jones

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