Introduction to Real-Time Processing

Final Cut Pro handles real-time processing with a feature called RT Extreme. The term real time refers to an editing system’s ability to calculate the final image while maintaining an acceptable frame rate and visual quality. In other words, you can see the results of an effect as soon as you play your video. Real-time processing is the opposite of rendering, in which you have to wait for an effect to be calculated and stored on disk before you can see the results.

For basic editing tasks, Final Cut Pro handles real-time processing automatically, keeping you focused on the creative choices at hand. However, if you work with a lot of effects or if you color correct video footage, you should take some time to learn the details about the real-time architecture of Final Cut Pro.

Being able to see your sequence play back in real time, regardless of the quality, is often more important than seeing full-quality video. By default, Final Cut Pro attempts to calculate video at full quality. However, it’s fairly easy to exceed your computer’s ability to calculate effects in real time and at full quality.

To maintain your creative pace, avoid rendering, and maximize performance, Final Cut Pro provides several real-time playback modes, such as Safe RT and Unlimited RT.

To learn about where you can change real-time playback settings, see Locations for Changing Real-Time Playback Settings.

To read detailed explanations about each real-time playback mode, see About Real-Time Playback Options.

Real-Time Playback Versus Rendering

For most stages of editing, reduced playback quality is more acceptable than losing the ability to play back effects in real time. Toward the end of a project, during the “finishing” stages such as color correction and output, you can choose to render at full quality to ensure the best results. For more information, see Rendering and Video Processing Settings.

Note: Final Cut Pro always displays real-time previews using 8-bit processing.

How Real-Time Processing Works

Consider a clip placed in a sequence. Even when no effects are applied to the clip, Final Cut Pro and your computer must do a certain amount of work to play back the media file associated with that clip: the hard drive must be able to read the frames of video as fast as they need to be displayed, and the computer processor must decode each video frame into uncompressed pixels that are then shown on your computer display.

In the past, even the most expensive computers could barely achieve the required hard disk and processor speeds. Editors often had to install specialized video cards that could provide the necessary processing power for playback. Today, personal computers can easily achieve video playback and still have a lot of processing power left to spare.

How Final Cut Pro Calculates Processor Workload

You can process your video footage in a remarkable number of ways: by adding video filters, adding motion effects such as scaling and rotation, making speed changes, adding transitions between clips, and compositing multiple video layers. All of these effects are really just mathematical operations performed on the pixels of your video. The more effects you add to a clip, the more operations are required to display the results.

Final Cut Pro analyzes a sequence to determine the processor workload required for playback. Different portions of a sequence may require different amounts of processing. Final Cut Pro breaks the sequence into segments and then indicates the processor workload for each segment with a colored status bar. For more information, see About Render Status Bars.

Figure. Timeline window showing status bars that indicate the workload for each segment.

For example: You edit a DV clip into a sequence. Final Cut Pro adds up the processor “expenses” of reading the media file from your hard disk and decompressing the DV frames. Because these processor “expenses” are fairly low, the color of the status bar over that clip in the Timeline indicates that real-time playback is possible.

Now you add a color correction filter to a clip. Playback of this clip is now more “expensive” for the processor because more calculations must be performed to display the result. Final Cut Pro compares the number of required calculations to the speed of your computer’s processor. If the processor “expenses” are low enough, the clip can still be played in real time, even with the additional color correction filter.

Achieving Real-Time Playback When Processor Power Is Exceeded

As you add more effects to a clip, more processing power is required to play that segment of the sequence. If too many effects are added, Final Cut Pro recognizes that the number of calculations is too “expensive” for the processor, and the color of the status bar changes to indicate that playback may still be in real time but no longer at full quality.

To keep your edit session moving and render-free, Final Cut Pro has several real-time playback settings that balance playback quality with a minimum of dropped frames. For a complete explanation of real-time playback settings, see About Real-Time Playback Options.

What Are Dropped Frames?

Dropped frames are frames that are unintentionally skipped during playback, either because the hard disk cannot keep up with the video data rate or because the computer processor cannot perform all of the applied effects in time. Some real-time playback modes allow dropped frames, while others require rendering to avoid dropped frames.

Dropped frames during editing are usually tolerable. However, during output, dropped frames are almost always unacceptable.

Identifying Which Effects Can Play Back in Real Time

The real-time status of effects can be identified in several places:

  • Timeline and audio clip item render status bars

  • Tooltips in render status bars

  • Filter and transition names in boldface type

About Render Status Bars

The presence of a colored status bar in the Timeline indicates that a clip requires some kind of processing. There are two render status bars above the Timeline ruler. The upper one is for video and the lower for audio. These render bars indicate which segments of a sequence will play in real time, the quality of playback, and which segments require rendering.

Figure. Timeline window showing status bars that appear near the top of the Timeline.

About Render Status Bar Tooltips

If you position the pointer over a render bar, a tooltip appears with information about the real-time or render status of that section of your sequence.

Figure. Timeline window showing a tooltip that indicates the status of a particular section of a sequence.

Effect Names That Appear in Boldface

In both the Effects tab of the Browser and the Effects menu, video transitions and filters that can play back in real time appear in boldface.

Figure. Browser window showing the Effects tab with real-time effects appearing in boldface.

A real-time effect appears in boldface based on:

  • The video format used by the currently selected sequence. Video formats that have higher system requirements for real-time playback result in fewer effects displayed in boldface.

  • The processing capabilities of your computer, such as the processor speed and the amount of installed RAM

  • The playback video quality and frame rate selected in the RT pop-up menu

  • The external video option you have selected in the A/V Devices tab of the Audio/Video Settings window, and whether or not it is turned on.

  • The capabilities of the currently selected video effects accelerator card (if you are using one for real-time video processing)

Note: The number of effects that appear in boldface may change depending on the current sequence settings and which real-time playback settings are selected.