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 should attach a stable and continuos reference signal to that input and enable the Ref In feature (in the software provided by the video card vendor). This will allow just:out to run synchronized and therefore frame accurate, which is even more important when using the redundant playout feature. Activating the built-in DSKeyer of an AJA device 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/