Most of the video devices available allow to attach a reference signal. Should i have a reference signal attached to my video card?
If your video hardware provides a reference signal input (commonly known as Ref In) you can attach a stable and continuous reference signal to that input.. This will allow just:out to run synchronized and therefore frame accurate, which is even more important when using the redundant playout feature. Activating an internal switch to live method (DSK or Buffered) means, that the video card synchronizes to the incoming video instead of the reference signal and therefore the incoming video must be stable. The signal attached to the Ref In is ignored in this case and we recommend to disconnect it.
In order to stabilize the AV signal in advance, i.e. before it's sent to the video card input, you can use frame synchronizers like this: http://www.aja.com/products/fs/
In case no reference signal and no live signal is attached, the video card will use the built-in clock, which is more or less accurate and therefore the master time will drift away from the reference time.