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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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We have talked about how to create smooth slow motion and how to create stuttery stop motion. Next, let's talk about freeze frames, how to stop motion altogether. You might have noticed that I have closed all my previous comps, just to clean up my display, and now I am going to open up the comp 13-Freeze Frame*starter. Let's say we have been given a job of creating a 20-second-long composition, but the most suitable clip we could find was just this 12-second-long shot. How can we extend this clip to fill the entire composition? Well, there's a couple of different things you could do.
One would be to open the Stretch column and time-stretch this clip to fit the entire 20 seconds of duration, then use frame blending to smooth out the motion. But sometimes some clips just don't look right when they are not playing at their natural speed. Let's audition this clip. We can see that there is a considerable amount of time at the start and at the end where there is no motion at all. We can probably extend this clip by putting some handle on to the front or end by extending under this ending pose or this beginning pose.
One approach would be to take a still image and just paste that in. However, there is cooler way of doing this inside After Effects. I am going to select my clip, and you can go either to the Layer menu and the Time submenu or just right-click directly on a clip and choose Time, and then choose Enable Time Remapping. Time Remapping gives you the ability to keyframe time, in other words determine what the frame of your source we will be seeing at what frame of your composition. If you look closely and go to the last Time Remap keyframe After Effects creates for you, you might notice that it's just beyond the end of your clip.
This was done for historical reasons. Back when most of the source material with interlaced video, they wanted to make sure you got every bit of source material, including the last field. However, these days a lot of material is progressive scan, no interlacing of fields, and having this keyframe pass through of your clip can occasionally cause problems. So what many users do is they press O to go to the outpoint of the clip, place a Time Remap keyframe there, and then go to that row glass keyframe and get rid of that. Once we have Time Remapping enabled, you might notice your layer bar has this gray area after it and before it.
This indicates that you can now extend the head or the tail of this clip. For example, I will just place my cursor over the tail of my clip. You'll see I get a two-headed arrow which indicates there's more material to reveal my source, and I can just drag it out to the end of my composition. Same thing for the head; I can go ahead and drag it out to start my composition. The little hash marks underneath indicate that you have now extended something before the beginning of your clip. Now we have our hold at the start, we pick up the motion, and then we have our hold at the end. Very simple.
This time-remap trick is great if all you need to do is extend existing head or tail in your clip. Let's say you needed to stop somewhere earlier than the very end of your clip. You scrub to the point where you want to stop, put a Time Remap keyframe there, go to your last keyframe and disable it, and now you will hold this frame of source material for the entire remainder of your clip. What if you don't want any motion in the middle? What if you just want to pick one particular or pose and have that act as a still image for the entire duration of your composition? I am going to temporarily turn off Time Remapping. Disabling the animation stopwatch for Time Remap actually makes the whole parameter go away, and now instead I will right-click again, choose Time, and this time choose Freeze Frame.
Freeze Frame will reapply Time Remapping, but will only place one hold keyframe at the Current Time Indicator. As you see in the Time parameter down here in the Timeline panel, that same value, that same frame of source will now be used for your entire clip. Now there is something to watch out for while you are using Time Remapping. If you've looked closely at this particular video clip, you might have noticed these little teeth along the columns here. I want to go ahead and zoom in so you can see this in greater detail. Those jaggy teeth are a tell-tale sign of interlacing, where these two fields captured at different points in time and interlaced on alternating lines present in the source material.
This is a very common video format. We recommend that any source material you bring into After Effects that has interlacing should have those fields separated for best performance in After Effects. That way you can get access to all of the visual information. To do that, I will select my clip, right- click on it, and choose Reveal Layer Source in Project, click on the Interpret Footage button for this clip, move this to the side so you can see both the clip and the Interpret Footage dialog at the same time, and choose Separate Fields.
All interlaced high-def video is Upper Field First, but this happens to be a NTSC standard-definition clip, and most of those are Lower Field first. When I choose that the good news is that my fields will be separated; the bad news is that After Effects was having to interpolate the missing lines for every frame it's displaying, so my visual resolution has gone down. I can use this Preserve Edges option inside Interpret Footage dialog, and that will improve thing a little bit. But in general, it's not great to have to freeze interlaced material, because that means you are going to freeze one field or only half of the visual information possible.
If you have a choice, we recommend that you shoot progressive scan, not interlaced, on your cameras. That will give you lot more flexibility to do freeze frames and other time- remapping tricks later. And speaking of time-remapping tricks, that's the subject of the next section.
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