From VidvoxWiki

Grid Pro Manual
Getting Started
The Basics Managing Media Playing Movies The Mixer The Sequencer Using FX The Preview Screen
Advanced Features The Gesture Slider Controllers The Fontsynth The Audio Player The DVR Shortcuts The Preset Manager
Optimizing Grid Pro

Using the Preview Screen

The Preview Screen can be used to view any video stream in GRID Pro without having any effect on the main video output to a secondary display. You can switch between sources - bus a, bus b, mixer - using the source picker below the preview screen. To cycle through sources, one by one, hold option while clicking anywhere in the preview screen.

Once you have selected a source, you can pick whether to view the source before or after FX processing. To toggle between pre and post FX, click anywhere on the preview screen, or the yes/no button below the preview screen.

The preview can also use a special "Quad" mode which splits the screen into four smaller previews, allowing you to view multiple video streams at once. When using Quad mode, four menus will appear below the preview screen for selecting the sources for each quadrant. To activate Quad mode, click the QUAD button in the source picker, or hold shift while clicking in the preview window. To leave Quad mode, select any other source from the source picker, or shift click on any quadrant to have it fill the entire preview screen.

Display modes and priority

The preview screen can use one of three different graphics modes for displaying video on screen: Quicktime Acceleration, OpenGL Accerlation, or no hardware acceleration. The optimal setting will vary depending on your graphics card. The currently selected graphics mode can be changed in the GRID Pro preferences under displays, or by using the Displays menu.

When using the main output screen or recording to disk, the preview screen can be set to a low priority mode or turned off to increase the framerate.