I'm on a MAC PRO with the OS 10.6.8 and 8Go Ram, the problem is when i turn on my preview video on the Blackmagic the video monitor is not in real time and the after effect is so slow. When i put it off (computer monitor only) it's ok but i havn't my video monitor of course....and i need it. Is there some tricks for having my black magic (1080 i 50) ON and a RAM Preview in real time ??? ! My drivers Black magic is the 9.5.3 it's the highest driver for MAC OS 10.6.8 + ADOBE CS6+ FCP7. Thanks for the read. ( i tried update adobe, change qt library, change aspect ratio, pixel, preview ram settings, change drivers black magic and other but nothing work )
No, there's no trick. There is simply a lot of overhead that goes into the video preview to the external monitor. We've made that a little better in After Effects CC, and we're making a large change in this area in a version for the near future.
What is the color bit depth of your project? (8, 16 or 32?) Have you changed that recently, or have you changed the frame rate or frame size of your comp?
Performance with video preview to an external monitor is almost always related to the pure bandwidth requirements of the frames you're sending to it. If the frames require more memory, it may be slower. Frame size, frame rate, and color bit depth all affect the memory requirements of the frames.
If none of those parameters has changed, troubleshoot the general performance of your machine. If there are other processes (look in Activity Monitor) that are using significant processor and/or memory resources, they may be causing a bottleneck for the frames getting out.