The devs do know about this and it is an in-progress issue. Also if you look in the Activity monitor you can see the OS thinks the processes are not responding, but in fact they are. Apparently the finding the fix has been extremely evasive.
It seemed like it got fixed for an update or two, but now it’s back more consistent than ever, on my system. For the past while I’ve been running Cubase with the video component hidden from it, but of course that’s not an option for you or many others…
complaints went down a lot since we found out the above workaround. However, as I can see from this thread this issue can still be triggered by something we don’t know yet. For now, I can only give you one other vague hint on this topic. The video warning message can also pop up in cases where the MediaBay is trying to scan files (audio and video) that are corrupt or cannot be interpreted correctly by Cubase. So please check if there are certain user folders that you’ve set up to be scanned by the MediaBay and that might contain corrupt files. Nevertheless, I’m afraid there is at least one more thing causing this issue and we are trying hard to find it.
I’ve unchecked my boot drive in the Media Bay just to be sure. The problem persists. I’ve posted above that I have no aggregate devices in AMS either. It seems also that video playback makes Cubase go progressively slower and slower in the course of two-three hours’ work, display updates become slow and unresponsive, and I have to quit and restart the session.
I went from OS X 10.8.4/Cubase 7.5.3 to OS X 10.9.5/Cubase 8.0.5 and the error started immediately when trying to open any project. I did have an aggregate device, removed it, and the problem went away.
So, in my case at least, it sounds like something that was introduced in Cubase 8 or something that changed in the OS.
This problem arrived with Mavericks and the way it behaves with the video engine. We already gave you the feedback that you need, it is caused by an aggregate device, please read the post above. In any case we are still investigating and we do not have any new information to share.
You can ignore this, the OS thinks they are not active or responding but in fact they are.