Wich is the way to see video preview in sync with the audio at the same time
There is an application called xjadeo, which syncs to JACK transport. it can run on OS X, but I do not believe that it is available as a binary (ready to run) download. It provides sample accurate video playback alongside Ardour (and other JACK aware applications).
Other than that, the options are weak - you would need a video playback application that could slave to or send timecode, and as far as I know most of those that do that are very expensive (Final Cut Pro etc).
I actually have a double-clickable .app of xjadeo 0.4.0, and it works great. But I can’t seem to figure out where I got it. Anyone know the link?