Hi,
I dont know if this sounds stupid and ridiculous to you, but I had a problem with FCP not playing back correctly myself on a G5 the other day, and just found out that the video in the canvas-window needed to be fully visible in order to play on the external Broadcast-Monitor (Decklink). So I pressed “fit window” and all was ok again.
thought I had to share this
regards Uwe Wiesemann