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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.
The After Effects Apprentice videos on lynda.com were created by Trish and Chris Meyer and are designed to be used on their own and as a companion to their book After Effects Apprentice. We are honored to host these tutorials in the lynda.com Online Training Library®.
Our focus in this first chapter will be on how to smooth out motion when you've had to change the speed of the clip in your project. If you have access to the exercise files that came with this video course, open up the project file AEA_Time Games.aep. If instead you're following along using our book After Effects Apprentice Second Edition, open up the project file that came with Lesson 7 Expressions and Time Games. Those who are using the project that came with the video course might notice that our comp numbering starts with 9 rather than 1. That's because this subject was actually taken from the second half of Lesson 7 in our book, but we thought it was important enough to treat on its own.
Open up the Comp 09-Frame Blending*starter. I've already queued up a quick RAM Preview, and I'll play it by pressing 0 on numeric keypad. You see what we have here is a very smooth fly-through along the tops of some clouds. But say the client--or you, for that matter--felt that this was a bit too fast and you wanted to slow it down. Well, you may remember from back in the After Effects Apprentice Layer Control Lesson, there is a couple of different ways of slowing down a clip: one is to go directly to the footage source in the Project panel, Aerial Clouds, open up its Interpret Footage setting, and change its frame rate there.
Another approach is to go into the Timeline panel, right-click on any column header in the Timeline panel, and select Columns > Stretch. This is how you get access to a parameter to time-stretch the playback on an individual layer. By the way, in some other programs this parameter is known as Speed, which is the inverse of the Stretch that After Effects uses. Let's say I wanted to slow this down so it's only playing back at one third of the speed it originally was. I can enter a Stretch Factor of 300% or I could enter new duration for the whole clip.
Notice that the Time Stretch dialog has a couple of additional options on how to stretch the clip, namely, what frame stays in its original position in the composition timeline? The in point, the current frame, which is where the time indicator is, or the out point. In this case, I want my in point to stay the same, so I will say Hold in Place > Layer In-Point. I'll click OK. I'll press 0 on the numeric keypad again to RAM Preview, and you might notice that we have a bit steppier of a playback now. It is slower, but it's not very smooth.
And if I halt playback and use the page down key to step a frame at a time through this, you'll hear I've got identical frame. There's a new frame, identical frame, identical frame, finally a new frame, identical, identical, new frame. What After Effects is doing by default is merely holding on a frame until it's time to call up a brand-new one. Well, there is a way to improve that, and it's called Frame Blending. Just like Motion Blur, Frame Blending needs to be turned on in two separate locations: for the layer and for the composition.
This column with the multiple filmstrip icons is the Frame Blend switch. You need to enable Frame Blend for the layer in that column. For now, just click once to where you get this dotted line. That indicates you are in Frame Mix mode, where After Effects will do a simple crossfade and blending of adjacent frames. Now, even though I've turned this on, you've noticed no change up here in the Comp panel, and again as I step through the Comp using page down, you're seeing a lot of repeating going on.
If you were to render this file, it would be smooth, but if you want to preview it here in the Comp panel with smooth motion, you also need to turn on the Frame Blending switch for this comp. This is basically a Preview switch. Frame Blending can take a little bit of time to render. That's why After Effects gives you the option of leaving it off while working, but we want to see its results. So as soon as I click this on, you'll notice a slight change in the Comp panel, and now as I step a frame into time, you'll see what appears to be smooth motion with every press of the page down button and every frame of motion.
I'll press 0 to RAM Preview. Now we have a nice smooth slow motion. Now, this Frame Mix mode with the dashed lines down here in the Timeline panel works really well for footage that has soft edges or is otherwise indistinct. Clouds work really great for it. If I was to use this Alien Atmospheres-- I'll hold down Option or Alt, drag it and replace the footage-- this would also blend very, very smoothly.
Even some footage that has a mixture of sharp and soft areas, like this Light Alchemy-- again, I hold Option on Mac, Alt on Windows and drag to replace the clip in my Timeline-- will still frame-blend pretty well. What doesn't blend well is a object that has very clear sharp edges and fast motion. You'll see echoes from the mix, and that's a problem we'll tackle and solve in the next movie.
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