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Discover how to manipulate time in After Effects. Author Chris Meyer shows how to stop, slow, and speed up footage, and how to combine these techniques with nested compositions, expressions, and the Graph Editor. Along the way, he reveals several important yet somewhat hidden functions, such as the advanced composition setting that ensures predictable stop motion, the Frame Mix and Pixel Motion modes of the Frame Blending switch, and the Time Remap parameter.
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To make this nested composition loop throughout the duration of its longer final composition, we need to do three things. The first one we discussed in the Quizzler challenge movie. You need to make sure your source composition indeed seamlessly loops. We did that by careful placement of our keyframes, and also by time stretching our looping background to make sure it, too, repeated when we got to the end of the composition. To test that, I am going to go somewhere near to the end of my comp, press the spacebar to play through the end, and make sure that it's seamless when it comes back to the head. And we'll play through one more time, seamless loop.
We have the source we need. Now, back in our final composition, we need to do two more things. First off, we want to manipulate what frame of this source is being played back at a particular time in our final composition. As soon as we talk about remapping frame of source to frame of comp, you should be thinking time remapping, and that's part two. So I'm going to select this layer, go up to Layer > Time > Enable Time Remapping, and you'll see it's automatically extended this nested comp to fill out the remainder of this composition; if it didn't, you just place your cursor over the end and drag it out to fit.
It hasn't created a pair of keyframes for us at the start, and if you remember, one frame past the end of our source comp. You might be tempted to try to start copying and pasting keyframes at this point, but you're going to end up with something awkward as you go from the first frame of source back to the last frame of source. The better solution here is to find a way of looping the duration of this comp. As soon as I start talking about looping, your mind should go back to the previous After Effect Apprentice lesson on expressions.
We mentioned one of our three favorite expressions was loop, and it wasn't a variation that could loop the duration of the source. Perfect! So I'm going to hold down Option on Mac, Alt on Windows, click on the animation stopwatch for time remap. That enables expressions, and I can either use the Expression Language menu to help me out or I remember the Loop expression by heart, because it's fairly simple. I want to loopOut. I want to continue from the out point of this composition onward. The duration time--not based on keyframes--and what I want to do is cycle, basically, repeat the content over and over, don't go back and forth like a ping-pong, don't offset in time but just cycle repeat what I have, comma. And my source composition was 5 seconds long. Close parentheses. Click off.
My expression has been accepted. Press 0 on the numeric keypad to RAM Preview, and you'll see that we now have a seamlessly looping composition playing out for the entire duration of this final comp. Now you might have noticed a particular glitch back here right around this keyframe, where the screen goes dark. This is another artifact of Time Remap defaulting to placing its second keyframe one frame past the end of your source.
This comp actually goes from 0 to 429. So as we mentioned earlier, what a lot of users do, as soon as they enable time remapping, is they go to that last keyframe, press page up to back up one frame, to the true end of the source, put a keyframe there, then go to that last keyframe and turn it off. As soon as you do that, we are now seamless through this particular gap. And just to approve the usefulness of this, I want to go back to the source composition, make some changes.
I'll press F3 to open Effect Controls, maybe change the color of one of these pulleys, maybe change the timing of one of these keyframes, go back to my final comp, RAM Preview again, and all of my changes have been picked up automatically and are included in this still-looping composition. That's why you use expressions: they allow you to go back and change your master for the expression and have those changes ripple throughout your composition. So now you've built quite a good skill set. You've combined the concept of nesting compositions with expressions with time remapping, and that's why we're teaching in this way.
We're giving you a series of building blocks that you can start to combine and reuse to solve your own problems on your own jobs.
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