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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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In the previous movie we showed how Frame Mix mode, indicated by this dashed line underneath the Frame Blend Switch column, can help smooth out slowed-down motion and soft amorphous footage. For example, we started with this Aerial Clouds. I'll hold down Option or Alt, drag it in to replace. You can see we had some very nice smooth motion. However, it doesn't always work that well. Open up the comp 10-Pixel Motion*starter, where we have this man walking around his car towards his plane. Yup! It looks like a tough life.
Notice that we already opened up the Stretch column and slowed this down by a factor of 300%, and again, you can right-click on any column header and choose or hide any of these columns. If I was to enable Frame Blending for this layer in Frame Mix mode and also turn on Frame Blending for this composition so you can see it previewed, you can already see these echoes, or ghosting, appearing around the edges of this man. That is the result of adjacent frames being mixed together to try to smooth out motion.
I'll press page down a few times to step through this clip. You'll see where it gets sharp, where we get back on a whole frame, but these intermediate frames exhibit some clear ghosting issues. You will see it on the car as well and a little bit on the plane. But this high contrast edge between his dark jacket and the bright sky really shows up the problem. Well, there is another Frame Blending mode known as Pixel Motion and to enable that, you just need to click on the Frame Blending switch one more time. I get a solid line.
You'll notice this line is sharpened up immediately, and focus on this edge of the jacket as I now step backwards in time back to the frames we were having trouble with. You'll see that we don't have any of that ghosting going on through his collar. What Pixel Motion mode is doing is actually looking at the motion of every individual pixel from frame to frame and trying to create brand-new in-between pixels, guessing where that pixel would have been if we indeed had shot, say, at a higher frame rate.
At first, this looks like magic, and you go, this is great! I'm going to use this on everything to make it look better. However, if you've been looking at other parts of the frame, like right around the Artbeats logo that's burned in here in the right corner, you notice some things are falling apart. Let's go to something very obvious, like where he is walking across this car. So he has motion in one direction, walking to the left, and the car has motion in the other direction as the camera pans and the car slides off to the right. Go down to around 120, where his arms start to swing in front of the car.
Now his arms are moving at a different speed than rest of his body. This is where it gets to be a bit too much for Pixel Motion to guess where all the pixels are moving to. You can see these weird interference fields moving across the windshield of the car and really wrecking it. So this is something you need to watch out for in Pixel Motion mode. Never just apply it and render assuming it worked fine. At the very minimum, RAM Preview the entire visible portion of the clip to make sure you don't have any weird artifacts like this appear.
This is the type of thing that makes a client reject what you thought was a final version, and then you're left scrambling trying to fix it. Now, if Pixel Motion doesn't work for you, and if Frame Mix is leaving too much ghosting going on, like around his collar here--I will step forward-- you do have a few other alternatives. Inside After Effects you can turn off Frame Blending, set your Stretch back down to 100%--you need to go back to where the clip actually is. Then apply Effect > Time > Timewarp.
Timewarp uses the same underlying technology as Pixel Motion but exposes all these parameters to you to help tweak. Now, I'm not going to go through all these parameters here. If you are really curious though, this is based on a technology called Kronos from The Foundry. If you go to their web site and dig up a manual on earlier versions of Kronos, such as Kronos for Final Cut, you will find an explanation of all of these parameters to help you dial this in. There is also a pair of third-party solutions: one, The Foundry has a brand-new version of Kronos called Kronos 5 which works even better, and secondly, Re:Vision Effects has long had this wonderful plug-in called Twixtor.
That's the one we've used for years to help smooth out motion on critical shots. So between Twixtor or Kronos 5 you should be able to crack problems that After Effects cannot solve with its built-in Frame Blending and Pixel Motion.
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