Summary
Some of the applications included with Final Cut Studio are able to display output to an external video device. Viewing such output on a precisely calibrated monitor is the best way to accurately evaluate color and framing of material that is intended to be viewed on a television. Apple Qualified video interfaces are evaluated with each of the Final Cut Studio applications that can access them for output. Other applications, such as iMovie HD and Final Cut Express also allow external video monitoring.
Issue
It's possible for a minor conflict to arise if a Final Cut Studio application is running at the same time as another application, which also uses external video output. If both applications are set to access the same video output device in such a case, switching directly from one application to another may cause unexpected results. In many cases, you might see an alert message, such as this one:
The video output device could not be opened.
This situation is merely a display characteristic; it won't affect your projects or your media.
Solution
In unusual instances, if the application has lost contact with the video interface, you can simply quit the application, then open it again. If you're working in two Final Cut Studio applications that require video output from the same device, you can quit the first application prior to opening the second.
If both applications need to be running simultaneously, you can set one of the two applications so that it will not output video. This should allow you to actively move between the applications with ease. Check the user guide under the Help menu for specific steps for each application.