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Red, yellow, and green render bars and what they mean

[Thanks to Steve Hoeg, who helped with some of the details of this post.]

(For a video that briefly covers much of the material in this article, go here.)

If you’ve worked with Adobe Premiere Pro even a little bit, you’ve noticed that colored bars—red, yellow, and green—appear at the bottom of the time ruler at the top of the Timeline panel, above clips in a sequence. These colored bars are often referred to as render bars. But what do they mean, and what does this mean to your work?


a digression into rendering…


First, we need to understand what it means to render a preview.

In the context of computer graphics, rendering is the creation of an image from a set of inputs. For Premiere Pro, this essentially refers to the creation of the frames in a sequence from the decoded source media for the clips, any transformations or interpretations done to fit the source media into a sequence, and the effects applied to the clips.

For clips based on simple source media that match the sequence settings and have only simple effects applied, Premiere Pro can render the frames that make up the sequence in real time. In this case, each frame is rendered for display just before the CTI (current time indicator) reaches it. Premiere Pro caches these results so that it doesn’t unnecessarily redo work when you revisit a frame.

For more complex sets of effects and more difficult source media, Premiere Pro can’t always render the frames of the sequence as fast as needed to play them back in real time. To play these frames in real time, they need to be processed and saved ahead of time, so that they can be read back and played instead of being recalculated on the fly. The creation of these frames to be saved for rapid playback is what is meant by rendering a preview.

By the way, it’s common but confusing and misleading jargon to refer to rendering of previews as rendering all by itself. Rendering for display, rendering for final output, rendering for previews—these are all valid uses of the word rendering. Don’t fall into the trap of using this general term to refer only to the specific case of rendering for the purpose of creating preview files for real-time playback.

Note: Rendering of previews is only for preview purposes. Preview files will not be used for final output unless you have Use Previews option checked on output—which you should not use except in the case of rough previews. Using preview files for final output will in almost all cases cause a decrease in quality. It can speed things up in some cases, so it may be useful for creating a rough preview in less time.


OK, so now about those colored render bars…


With that preparatory definition out of the way, what do the colored bars mean?

  • green: This segment of the sequence has a rendered preview file associated with it. Playback will play using the rendered preview file. Playback at full quality is certain to be in real time.
  • yellow: This segment of the sequence does not have a rendered preview file associated with it. Playback will play by rendering each frame just before the CTI reaches it. Playback at full quality will probably be in real time (but it might not be).
  • red: This segment of the sequence does not have a rendered preview file associated with it. Playback will play by rendering each frame just before the CTI reaches it. Playback at full quality will probably not be in real time (but it might be).
  • none: This segment of the sequence does not have a rendered preview file associated with it, but the codec of the source media is simple enough that it can essentially be treated as its own preview file. Playback will play directly from the original source media file. Playback at full quality is certain to be in real time. This only occurs for a few codecs (including DV and DVCPRO).

Note the uses of the word probably above. The colors aren’t a promise. They’re a guess based on some rather simple criteria. If you have a fast computer, then a lot of things marked with red may play back in real time; if you have a slow computer, then some things marked with yellow may need to be rendered to preview files before the segment can be played in real time.


what causes a segment to get render bars of a certain color


What kinds of things contribute to a segment getting a certain color of render bar? The general answer is that changes that tend to make processing of a segment much slower will switch it from none to yellow or from yellow to red.

I’ve broken the examples below into separate lists for Mercury Playback Engine GPU Acceleration and Mercury Playback Engine Software Only, which are the two possible settings for Renderer in the Video Rendering And Playback section of the project settings. (For details of CUDA acceleration and the Mercury Playback Engine, see this page for CS5 and this page for CS5.5.) Because Premiere Pro CS5 can use CUDA to accelerate scaling, deinterlacing, blending, and many effects, many things that cause a red render bar in software-only (CPU) mode only cause a yellow render bar in GPU acceleration mode. Even more things are accelerated by CUDA in Premiere Pro CS5.5.

Mercury Playback Engine GPU Acceleration:

  • yellow: The source media’s codec is computationally difficult (such as AVCHD). As mentioned above, only very few simple codecs don’t get a yellow bar; these include DV and DVCPRO.
  • yellow: The settings of the clip (e.g., pixel aspect ratio, frame rate, field settings) don’t match the settings for the sequence.
  • yellow: A CUDA-accelerated video effect or transition has been applied to the clip. (A CUDA-accelerated video transition only causes a yellow bar over the duration of the transition.)
  • red: A non-CUDA-accelerated video effect or transition has been applied to the clip. (A non-CUDA-accelerated video transition only causes a red bar over the duration of the transition.)

Mercury Playback Engine Software Only:

  • yellow: The source media’s codec is computationally difficult (such as AVCHD). As mentioned above, only very few simple codecs don’t get a yellow bar; these include DV and DVCPRO.
  • red: The settings of the clip (e.g., pixel aspect ratio, frame rate, field settings) don’t match the settings for the sequence.
  • red: Any video effect or transition has been applied to the clip. (A video transition only causes a red bar over the duration of the transition.)

I hope that from this you will see that a yellow render bar doesn’t mean that something is wrong. It’s entirely normal for most modern codecs. And even a red render bar is to be expected with certain effects or when you are using media of various formats in a sequence. If you see a colored bar, don’t panic.


how the render bars relate to playback commands


One of the primary uses for the color bars is to give you the ability to render preview files more selectively.

  • When you press the spacebar, Premiere Pro plays the sequence without rendering any additional preview files first.
  • When you press the Enter key (or choose Sequence > Render Effects In Work Area), Premiere Pro renders preview files for all segments with red render bars before playing the sequence.
  • Unfortunately, there isn’t a default keyboard shortcut for the Render Entire Work Area command. The Render Entire Work Area command renders preview files for all segments with red or yellow bars before playing the sequence. I have customized my keyboard shortcuts to map this command to Shift+Enter.

a simple example


software-only
Above is a sequence in a project set to Mercury Playback Engine Software Only. The footage is 4K RED Cinema footage that matches the sequence settings. The first clip has a non-CUDA-accelerated effect applied. The second has a CUDA-accelerated effect applied. The third clip has no effect applied. The difficult nature of the footage causes it to be marked yellow for “probably will play in real time”. Any effect on these clips in software-only mode causes them to be marked with red render bars.

GPU
Switching the project setting to Mercury Playback Engine GPU Acceleration causes the CUDA-accelerated effect to get a yellow render bar instead of the red render bar that it got in software-only mode. The non-CUDA-accelerated effect is still marked as red, though.

render effects GPU
I pressed Enter to just create a rendered preview file for the segment with the red render bar…

render entire work area
… and then pressed Shift+Enter to use my custom keyboard shortcut for Render Entire Work Area.

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