FCP 7: Creating Speed Changes

[ This article was first published in the February, 2011, issue of
Larry’s Final Cut Pro Newsletter. Click here to subscribe. ]

Jonathan Levene is a new intern we have working with us for a month or so, and he suggested this next article on creating speed changes in Final Cut Pro 7.

Apple rewrote both the Constant and Variable Speed change interface for FCP 7. While I’ve covered this in my webinar and video tutorials, I realized that I haven’t written an article on it. So, at Jonathan’s urging, here goes.

CONSTANT SPEED CHANGES

There are three “rules” about constant speed changes:

1. A constant speed change changes the speed of the entire clip by the same amount.
2. If the audio and video of a clip are linked, then a constant speed change affects both the audio and video.
3. A constant speed change has the option to change the duration of a clip.

Here’s how it works:

1. In either the Viewer or the Canvas, select the clip with the duration you want to change. (Although you can select multiple clips and change all their speeds at the same time, I generally work with one clip at a time.)

NOTE: In the example above, notice the position of the cursor marking the end of the clip. I’ll come back to this in a minute.

2. Select Modify > Change Speed (or type Cmd+J).

3. The Change Speed dialog appears. At the top, either enter the new duration you want the clip to run, or enter the speed you want the clip to playback.

Changing Duration in this dialog box always changes the speed of the clip, even if you have plenty of extra video in the handles of the clip.

4. In this example, we are reducing the speed of the clip to 50% of normal speed. All the other settings in this dialog remain at their defaults.

Notice that the clip’s duration is longer than when we started – reference the position of the cursor for comparison to where the original clip ended. This is because, by default, Final Cut plays every frame of the clip from the In to the Out – and because it is playing these frames more slowly, the duration of the clip MUST change.

If you look closely at the end of the clip name, notice that the new speed of the clip is displayed in parentheses.

You can also see if a motion effect, such as a speed change, has been applied to a clip, by clicking the Toggle Clip Keyframes button in the lower left corner of the Timeline.

Any clip, whether selected or not, that has a dark blue horizontal line under it has had a motion effect, such as a speed change, applied to it.

NOTE: If the clip had a filter effect applied to it, a green line would appear under the clip, as well.

So far, this behavior is the same in all versions of Final Cut Pro.

What’s new with FCP 7, however, are the icons in the middle of the dialog and a new checkbox at the bottom.

The big news for Constant Speed changes in FCP is the Ripple Sequence checkbox. When this is checked, FCP plays every frame from the In to the Out of a clip. This means that the duration of the clip MUST change – either longer (for slo-mo) or shorter (for time-lapse) – because of this requirement.

However, when Ripple Sequence is not checked, FCP changes the speed of the clip, but does NOT change the duration of the clip. This means that for slo-mo clips, FCP will start at the In, but only play as many frames as will fit into the original duration, not displaying frames toward the end of the clip.

Or, for time-lapse, FCP will play as many frames as necessary past the Out, in order to retain the original duration of the clip.

NOTE: When you speed a clip up, if you do not have enough frames after the Out to support the speed you’ve chosen, FCP will shorten the clip and leave a gap in the Timeline.

The other very helpful new feature is the ability to add acceleration and deceleration to the start and end of the speed-changed clip.

In this example, I am:

• Slowing the clip to 50% speed
• NOT changing its duration in the Timeline by unchecking Ripple Sequence
• Adding an Ease-In ramp so that the clip slowly transitions from normal speed to slo-mo at the beginning, while slowly speeding back up to normal speed at the end. (You see this in the Start / End icons that I’ve clicked.)

The amount of the easing is determined by the two Smoothing numbers on the right side. The smaller the number, the less the easing effect. Normally, the default settings will be fine, but for very short clips, you may want to adjust these a bit smaller.

Frame Blending seeks to decrease the jerkiness when you are creating very slow clips. It has no effect on fast-motion clips. For best quality, leave this checked.

NOTE: Motion and other third-party speed change software use more sophisticated math — Motion calls it “Optical Flow” — to invent pixels for intermediate frames on extremely slow clips that smooths the movement even more. However, FCP does not use that technology. See the section at the end of this article.

Scale Attributes affects any keyframes you’ve set for other motion or filter effects. When Scale Attributes is checked, keyframe positions will be adjusted based on the revised length of a clip. Again, you would generally leave this checked.

VARIABLE SPEED CHANGES

Just as there are “rules” about constant speed changes, there are also three rules about variable speed changes:

1. While a variable speed change could change the speed of a clip by a single amount, it is designed to allow different parts of the same clip to play at different speeds.
2. A variable speed clip only affects the video of a clip, whether linked to audio or not.
3. A variable speed change never changes the duration of the clip.

Here, Apple made the most changes to the interface. In the past, we would make variable speed changes in the Motion tab. Now, everything is done in the Timeline.

While there are a couple of ways to do this, here’s my favorite method.

1. Click the Toggle Clip Keyframes to display the time hash marks at the bottom of every clip.

These hash marks (surrounded by a red box that I drew to highlight them) represent the speed of the clip. When they are evenly spaced, as they are here, the clip speed is constant. Slowing down a clip spaces these hash marks more widely, speeding up a clip squeezes them closer together.

In this example, I want to start the clip at 100% speed, slow it to 50%, then speed it back up to 100% at the end. Then, we’ll add some acceleration settings and see what happens.

2. Select the Speed tool – I call it the “Stopwatch in a Box” – keyboard shortcut is SSS.

3 Using the playhead in the Timeline, find the frame you want the speed change to start on. (You need to use the playhead, because you can’t view a clip while dragging the Speed tool.)

4. Then, using the Speed tool, click the clip at the position of the playhead. Notice that you just set a keyframe in the hash marks at the bottom of the clip. (If the hash marks are not displayed, you won’t be able to set a speed keyframe. Also, you need to click on either the clip or the hash marks.)

5. Find the location where you want the speed effect to end and set another Speed keyframe.

NOTE: Keep in mind that when you change the speed of a clip, the position of the second keyframe is going to move. You will need to allow for this in the clip. You’ll understand this problem better when you first change the speed of the clip.

6. Notice that here, I’ve created two keyframes in the middle of the clip — roughly equally spaced from the ends. FCP automatically created two more Speed keyframes – one at the In and the other at the Out.

7. Here’s the key point: Using either the Speed tool or the Arrow tool, Control-click on the hash marks BETWEEN the two keyframes where you want the speed change to occur and select Change Speed Segment.

This opens the Change Speed dialog we first saw when making a Constant Speed change.

8. Set the Rate to 50% and click OK. Notice what happened to the hash marks in the Timeline.

The hash marks got a lot more widely spaced, indicating that the speed of the clip, for that portion, has slowed down. Notice also that because the rate changed, the speed keyframe on the right changed position by moving farther to the right. This is because the keyframe is tied to a specific frame in the clip, not to a position in the clip itself.

9. Now, Control-click the segment you just changed the speed for and select Speed from segment start > Curve from Start. This adds a deceleration keyframe starting at the keyframe so the video gradually slows down to 50%.

You could do the same thing from the Change Speed dialog box. To open it, Control-click between the same two keyframes and select Change Speed Segment.

10. Next, Control-click, again, between your two speed keyframes and select: Speed from segment start > Curve Centered on End. This creates a gradual acceleration centering on the ending keyframe. (Pick the acceleration you like. You can use any combinations of these choices you prefer. I’m using different ones in this example just so I can illustrate what they do.)

You can see the results of your work by looking at the hash marks below the clip. The deceleration starts at the first keyframe, slows in the middle of the clip, then starts speeding up before the next keyframe, but doesn’t finish until after the second keyframe.

New with Final Cut Pro 7 is the ability to more precisely control keyframes, plus the ability to easily add acceleration and deceleration to any keyframe.

WHEN YOU NEED GREATER SPEED VARIABILITY

However, this whole system of speed changes breaks down if you select extremely slow speeds. Frame blending essentially performs a dissolve between each frame. This dissolve becomes really obvious when you slow a clip down to 10% speeds or slower.

With extreme slow motion, it doesn’t work at all. Motion provides Optical Flow, which can significantly increase quality, but in my work, I’ve found it to have problems separating the foreground from the background clip.

In order for Motion to work well, the foreground needs to be significantly different in color or contrast from the background. Even then, it can be tricky.

You might be better off to turn to third-party plugins. Probably the best-known is Twixtor by Re:Vision Effects. This plug-in works with a variety of different software, including After Effects, Motion, and Final Cut Pro.

Here’s a website where you can learn a lot more about it:

http://www.revisionfx.com/products/twixtor/

UPDATE – March 3, 2011

Andreas Kiel adds:

Just another note. It’s about frame blending with speed changes.

The way you describe is totally correct. And there is a thing which often is overseen – it’s the frame-blending.

FCP does a pretty good job on that even though I only use it for a rough cut and go to AE with Twixtor later.

To get a decent time remap you should enable frame blending. If you work with ‘P’ material you probably get more obvious ‘blended’ frames. When you stop the time remap at a wrong keyframe the blending will stay for the rest of the clip — that might be bad. So to make sure you don’t have unwanted ‘blending’ make a cut at the last keyframe (and/or first) and remove the time remap from those. It’s often not obvious that you got frame blending on this kind of editing, but I think it’s a good idea to do it that way especially when you work with ‘P’ material.

Larry replies: Thanks, Andreas.

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