Final Cut Pro HD | H•O•T Hands-On Training [Electronic resources] نسخه متنی

Understanding Rendering

Depending upon the speed of your computer, when you create a transition, you will see one of three colored bars at the top of the Timeline. These bars are called render bars. They indicate whether a transition or effect will play in real time or require rendering.

"Rendering" is simply a fancy word that means that the computer needs to calculate the effect you are creating before it can play it in real time. Many effects, such as dissolves, or motion effects, or some filters, can play perfectly in real time without needing to be rendered first. On the other hand, drop shadows and motion blurs always require rendering.

Although it seems like there's a whole rainbow of render bar colors, there are only three you really need to pay attention to: green, orange, and red.

Green render bars indicate that an effect or transition can be played in real time, without requiring rendering, until you are ready to output to tape.

Red render bars indicate that your computer is not fast enough to play the effect in real time. So, in order to see an effect that requires rendering, you need to do one of three things:

Render the effect (Sequence > Render All, or Sequence > Render Selection).

Press Option+P to play the clip as fast as the computer can calculate the effect from the position of the playhead, without first rendering the clip. (This is my absolute favorite keyboard shortcut.)

Choose Tools > QuickView.

The QuickView window opens to the same size as the Viewer with a little timer at the bottom. What QuickView does is build a RAM preview of your effect; in other words, it calculates the effect and stores it temporarily into memory. Then, starting at the position of the playhead, it plays your effect forward for half the time indicated on the timer. Then, it backs up the full distance of the timer and plays the effect in real time in the small QuickView window.

The benefit to using QuickView is that, after the first time through calculating your effect, you'll see the effect in real time. The thing I don't like about it is that it requires me to put my playhead in the middle of the effect, then calculate how much time I need to see the effect. Plus, it won't play anything longer than 10 seconds.

For these reasons, I almost never use QuickView, but use Option+P all the time.

[View full size image]

If you look really closely at the render bar line, you'll notice it's divided into two sections. Video renders are indicated in the top half and audio renders in the bottom half. An audio render is required if the number of audio tracks (or effects) exceeds the computer's capability to play them simultaneously in real time.

You can set the number of real-time tracks your computer can play in Final Cut Pro HD > User Settings > General. (The Audio Playback Quality setting determines the quality of audio playback on the Timeline. The "Low" setting is a good choice. Audio quality will always be high for final output.) Generally, keep this track setting small, so that more of your CPU is reserved for processing video, rather than audio.

There's one more thing you need to understand about rendering and that's Safe RT versus Unlimited RT.

Apple has worked really hard to bring more real-time effects to Final Cut. Obviously, the more real-time effects, the less time you waste waiting for the computer to render. The thing is, see, there's real-time and "real-time."

You change the setting in the top-left corner of the Timeline by using the RT pop-up menu.

Safe RT plays all green bar renders in real time, exactly as it will output. (Well, "exactly," depending upon the video playback quality setting in your preferences.) If you always want to know what your effects will look like, set Final Cut to play using Safe RT (this is the default).

Unlimited RT give you more real-time effects by dropping calculation-intensive portions of the effect. For instance, drop shadows, motion blurs, feathered edges are all calculation-intensive effects. So, Final Cut does not display these in Unlimited RT, so that you can view the rest of the effect to decide if you like it. If you are doing an effects-intensive production, running in Unlimited RT can save you a ton of time in previewing your effects, because not all effects need to be perfect in order for you to decide if you like them. Effects that are playing in real time but not with all elements are indicated by an orange color in the render bar.

Most of my productions are not effects-heavy, so I run my system in Safe RT. However, this is purely personal preference because all effects will be fully rendered at the highest quality before outputting to tape.