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As of version CS6, After Effects has made some major changes in the way that it manages the cache of your previously rendered and previewed frames. After Effects refers to this as its Global Performance Cache and that encompasses both RAM and disk-based caches, and these are the subjects I want to cover in this sidebar movie. As you may know by now, when you have performed a RAM preview on a composition, this green bar will indicate frames that have been cached or previously calculated and stored in RAM.
They need to be stored into RAMS so that After Effects can play them back in real time for your preview. Any change you make to your composition will cause this green bar to be erased, indicating it no longer has proper frames stored in RAM. For example, if I change the initial scale of the snowflake layer to 95%, you'll see that the green bar has disappeared just for the range in between those two scale keyframes. From the second scale keyframe onward, the value remains the same, so there is no need to invalidate or remove those cached frames.
If I wanted to preview this composition again, I would need to press 0 on numeric keypad or otherwise start a RAM preview. After Effects would calculate the missing frames and they can preview the entire composition once it has a green bar for the entire length of your work area or comp. However, big change in After Effect CS6, is you can now go back to previously cached states and After Effects will retrieve those frames that were previously thrown away. If I go ahead and move my time indicator back to the side of this comp and Undo my Change Value, I'll go back to my 100% scale for this first keyframe and I will still have a green bar above my timeline.
What After Effects has done is reached into its RAM, pulled these previously cached frames out of it and restored them in to the current preview cache. This will save you a lot of time you're playing what if. For example, I can go ahead and Redo my Change Value on a keyframe and I will not lose my cache, because After Effects knows I've previously rendered these frames, let's use these instead. You can also do things like apply Effects, edit them to see how you like their effect. I'll go later in this composition, decide I don't like that blurry snowflake, turn off the effect, and you'll see the green bar reappears as After Effects finds frames in memory that matches the current state of the composition.
So it's very cool, and indeed this is not restricted to the same composition. I can take this composition, duplicate it, open up this second comp, and you'll see a green bar appear for it immediately even though I've not RAM previewed this comp yet. That's because After Effects has analyzed this particular combination of layers and parameters, realized it has already calculated this condition or this state before and restored the cache from those previously calculated frames were in memory. Very nice. If I want to have a second version of this, I can go ahead and change this to something like, let's say 80% for this first keyframe.
I can either RAM preview this now, or take advantage of another feature, introduce an After Effects CS6, which is Composition Cache Work Area in Background, the shortcut is Command+Return or Ctrl+Return. This means, if you have a busy project with a lot of compositions you don't need to wait for each composition to fully preview before you can go on to the next comp. You can say cache this one on the background and change to your previous composition and continue working while the other comp is now rendering in the background.
The Info panel keeps you informed of what's going on, including when it is done with the other composition. I can switch back to other comp now. And now, we'll see a blue bar for those frames that it calculated. A blue bar indicates that these frames have been cached to disk not to RAM. In the case of Composition Cash Work Area in Background, After Effects is trying not to take away from the RAM you're using while working on another comp, because using other resources is using a processor you're not using right now and saving those frames off to disk. Whenever you want to preview a composition that has frames on the disk rather than in RAM, you just RAM preview again, and it will quickly load them from disk into RAM and playback to preview.
Another nice improvement in the way After Effects handles this cache is that when you save a project, it will transfer this RAM cache for particular slow or difficult to calculate frames, to the disk cache. After Effects makes a judgment, whether or not a frame would be easier just to render all over again or to store off to disk and retrieve and chooses the faster option. I can hit Command+S to Ctrl+S to save this project, but to drive a point home, I'm actually going to quit this project and pretend that I came back another day.
Let's say, it's the next day, you start up After Effects again, it'll take a moment to initialize, and you reopen a previously cached project, so just the one we were just working on. I'll open this one and you'll notice that these cache bars will automatically fill in. When I saved and quit, what After Effects did was save the RAM cached frames to the disk cache, and now that I've reopened the same project, After Effects when looking through its disk cache and found out that it still had frames connected to this particular project.
In this case, After Effects made a decision that it would be just as quick to render these simple frames as we retrieve them from disk, that's why you don't see a blue bar, but just the act of scrubbing the time indicator through these frames causes them to be rendered into RAM. But you might ask why is the bar blue instead of green? Again, After Effects does not want to waste resources, so it's keeping these frames on disk until you say you need them. If I go ahead and press 0 on the numeric keypad to initiate a new RAM preview, it will copy those frames from disk into RAM very quickly, faster than it could render and I get a near immediate preview of a project that I had already closed and quit from my previous work session. Very nice.
It's a feature you don't see on the screen, but it's going to save you a lot of time when you're working on projects. Now one more point about this disk cache. I'm going to open up the Preferences > Media & Disk Cache and there's a very important tip in this dialogue. For improved performance, choose a disk cache folder on a fast hard drive or even better a solid-state drive; the faster your cache drive, the more After Effects will use it, because that drive will be faster than re- rendering frames, and the faster that those frames will be retrieved from disk and put back into RAM.
Now the default happens to be your system drive and that's not really your best drive for your cache because your system is competing for resources on that drive as well. The best thing you can do is choose or even install another fast drive and point the cache to that. In this case I have a RAID attached to this computer. So I'm going to choose folder, this isn't the current folder that After Effects is using for my cache. Go over to a folder I created earlier on my RAID drive, choose that one instead, and now I will get much faster cache performance.
Don't confuse the disk cache with the Conformed Media Cache; this one is for MPEG and other format files and After Effects used to decode and convert into something and access more quickly. You can empty the disk cache if you need to. You can have multiple disk caches. Some freelancers will actually dedicate a different folder per client or per project, and if necessary, copy and move that cache folder with them, say if they have to go into remote location to work. But most important thing is put it on your fastest drive, give it a lot of room. I'm going to bump this up to 100 GB, just so I can save more frames for more projects on to my disk drive and will speed up your working practices in After Effects.
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