I have a similar but simpler issue, I’m editing multicam in FCP 7, 4 cameras, all footage converted to standard Pro Res 1280 x 720. My problem is that during playback, after around 4 or 5 seconds it freezes up, the audio chokes but then kicks back in about 2 seconds later and continues to play while video in the viewer is frozen. I always have the sync open selected in the viewer and canvas menu.
I tried turning playback to low quality in the RT menu and no change. Other settings there seem correct- safe RT, full frame rate for playback and multiclip playback checked. My sequences match my source footage, I’m editing off FW 800 drives, and here are my imac specs- intel duo core 2.66ghz with 4GB, 256 MB vRAM.
I do this every week and this issue is frustrating but also seems intermittent. Any thoughts?