First thing, I'm sorry for my English, it's really awful. I'll try to do my best. I'm a video editor. I recently had to buy a new iMac 27inch (OS X Yosemite 10.10.2 - 3,5 GHz Intel Core i7 - RAM 16 GB - NVIDIA GeForce GTX 780M 4096MB). Usually I work on FCP7, but on this new machine I have encountered an unusual problem when I try to do A/V sync. If i put in sync audio and video "on the clapperboard", at the beginning of the clip, in the space of a few minutes the clip go out of sync, considerably. With Premiere Pro (using same clips, audio and video) I don't have this problem. And, obviously, this problem does not exists on my old Mac with old OS. Why? Someone can help me?