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One of the great features Motion stole from Shake is optical flow and that's really the engine that powers retiming footage in Motion. So it's important before we get started with this lesson to make sure that we have some settings correct in preferences. So go up to Motion, in Preferences and let's set our Cache. At the bottom we have Optical Flow Retiming. We want to make sure to choose a folder to save the cache that gets build up as Optical Flow computes the different images.
When you slow down footage to a certain degree, let's say it's 24 frames a second footage and you slow it down and the computer has to play it back at 12 frames. Optical Flow has to actually generate the extra frames in between to create the image and this is actually one of the most powerful engines in the industry and it does a really good job doing this. But obviously, when you slow things down, everything has a breaking point. So just kind of keep that in the back of your mind. So before we get started, make sure to choose a folder on your hard drive or an external drive to save your cache.
Go ahead and close your Preferences, let's select the footage and press Play. And it takes quite a while but eventually you'll see this little runners appearing over the hillside. I'm going to stop playback just for a second. I set the play range to be the shot on purpose because I would like the move to actually be finished by around frame 300. And you'll notice this clip is a lot longer than that section. And this is actually a really good thing.
When you're retiming footage, it's always nice to sort of have extra frames. Move your playhead back to the beginning of the Timeline and let's open the Inspector. In the Properties section at the bottom, you should see Timing. And by default Time Remapping is set to Constant Speed. So anytime you drop footage in your canvas it plays back at normal speed. If you click on the pop-up menu, let's change this to Variable Speed. Now you notice Motion has already added a keyframe. You can see that because of the black diamond here.
Now as I move my playhead around and make changes, I want to make sure more keyframes are added. So make sure to turn on automatic keyframing. Press the Record button there and you know automatic keyframing is on because you see the pink in the different value sliders. Well, for some reason, these aren't pink, but I wouldn't worry about it. It's definitely recording the keyframes. Let's move our playhead down to around frame 48. This is why I want the runners to be fully in screen but still kind of off to the left-hand side here.
So in order to bring the runners on screen, this Retime Value is actually the frame number of the clip that we are retiming. So the playheads are on frame 48, the Retime Value is on 48, we are seeing frame 48. Let's click-and-drag in the Value slider way, way up. Okay, let's drag it to around 950. Now, what's happening, in 48 frames this footage is going to be retimed to play 950 frames.
Let's move our playhead back to the beginning so we can watch that. Press Play. That's pretty cool but now they are slowing down way, way, way, too slow. So let's stop playback for a second and open up the Keyframe Editor, Command+8 on your keyboard. Here in the Keyframe Editor, you can see the velocity is pretty much flat. So let's move our playhead towards the end of the clip here and click-and-drag to change the Retime Value, let's have the guys go completely off the screen.
Now if you notice it's still going to be pretty flat, I think that's probably a little too slow, so let's decrease the value on the Keyframe Editor just by clicking on this individual keyframe and dragging it directly down. Now I'll move your playhead back to the beginning and press Play, and you'll see the guys coming and they slow down a little too far away. So let me undo that. We'll just move it a little bit back up again. There we go. It's kind of a meet ground, move your playhead back to the beginning and press Play.
This is looking great. Now there is one last thing that we want to check and that's at the bottom of the Inspector. Go and stop playback for a second and let's look at these guys. Right now, there is no Frame Blending on. So what's happening, the computer just randomly slowing the footage down and whatever footage is there, it's showing me. Now we have three choices. We can turn on Blending. Let's see what that looks like. You notice it's blending the different frames so it may be taking frames from two or three frames ahead and two or three frames behind, and blend them altogether to create one frame.
Let's look at Motion-Blur Blending. You see a difference there. It's very slight. Let's move our playhead back in the Timeline a little bit so we can see a little more with this first guy. There is Motion-Blur Blending. There is Blending. It's minimal but I kind of like the Motion-Blur Blending. Now the last option is Optical Flow. When you turn this on immediately you'll get this little progress wheel and that's letting us know that Motion is now starting to cache the extra files it's creating in that area that we reset in our Preferences.
As I'm looking into image, it looks pretty good but honestly I think, I like the Motion-Blur Blending option a little better. So let's go ahead and change that back, turn off our automatic keyframing, move our playhead back to the beginning, close the timing pane, Command+8 and press Play. So we have just completed retiming in the Inspector and I hope you've learned a little bit about optical flow in the process.
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