We're experiencing a 5D de-sync with external audio. The external audio starts in sync with the video, but falls off over time.
I'm suspecting the de-sync is because of a framerate issue. What was the standard conversion process for 5D? I set it to process from h.264 to ProRes 422, same frame size, uncompressed audio, but was I supposed to set the framerate to either 59.97 or 29.97 to keep things in sync? Anything else I'm missing?
Second half deals with correct procedure for importing audio assets into FCP BEFORE syncing. First half deals with a method of fixing it if you have a complex timeline that needs fixing. In your case it is likely that you haven't done a whole lot of editing with drifting sync.