Two SDI inputs are perfectly sync?

Hi,

I am using a DeckLink Duo 2 to capture 2 SDI videos.
When I capture 2 inputs (as SDI A(for FILL) SDI B(for KEY)) at the same time, are these inputs perfectly synchronized?
Or, since these 2 inputs are internally different device, so does the capture timing shift?

If I want to capture SDI as perfectly synchronized FILL + KEY,
1) using 1 input as RGBA
2) using 1 input as SideBySide(Dual Link?)

Any other ideas? or related post?
Please advise me.

Thanks,

Takuma Ohya

You seem to be asking if the two channels of the Duo are synchronized. I think a more important question is are the two devices providing the sdi inuts synchronized? If they are cameras I think the answer will be no unless they have an external timebase input feature driven by an external timebase generator.