To display a frame from a sequence that has a video effect applied, the Avid editing application must calculate the result of the effect at that frame. For example, to display the midpoint frame from a dissolve between two clips, the application must calculate, for each pixel in the frame, a 50 percent blend between the color and luminance values in the outgoing clip and those in the incoming clip. To display frames in real time, the application must be able to performáenough of these effect calculations per second to maintain the appropriate display rate for your project, for example 30 frames per second (fps) for NTSC video.

Because your computer's processor and memory capabilities are finite, your Avid editing application's ability to play back effects in real time is limited. Effect calculations are more complex for some effects than for others, and still more complex when many effect options have been adjusted or when multiple effects apply to the same frame in a sequence. Even the fastest and most powerful system might eventually reach a point where it can no longer maintain real-time playback.

When the Avid editing application is unable to maintain real-time playback, it continues to play at the correct rate but does not display frames that it cannot process quickly enough. If the application is having only a small amount of difficulty with the complexity of the sequence, you will probably perceive a short stutter in the video playback, but you might still be able to get a useful sense of how your effects will look once they are rendered. If the application is having more difficulty, it is less likely that you will be able to judge the look of the effects.

You can use the following methods to control how real-time effects preview operates: