Slow Motion (Time Stretch) Tutorial for After Effects

After Effects April 19, 2021 5 min read

Slow-motion has many uses in videos, from creating stunning slideshow backgrounds to adding a narrative’s emotional context. Whatever your reason for creating a slow-motion sequence, you can’t go wrong with using this effect in After Effects. In this tutorial, we’re going to look at a couple of ways you can create super cool slow-mo in Adobe After Effects.

Part 1: Learn Basic Smooth Slow Motion in After Effects

There are 3 ways to create slow-motion effects in After Effects: time stretch, timewarp, and time remapping. In this tutorial, we will look at the first 2, but if you want to find out about time remapping, you can check out this handy guide.

The first step is to trim your footage to the correct length before you apply your speed effects. You should also make sure your composition is long enough for your clip once the speed effects have been added. Once you’re happy with the clip you want to slow down, choose either the Timewarp or Time Stretch methods below.

For the best slow-motion shots, you should film the footage at a higher than the standard frame rate. The frame rate tells you how many images per second are being recorded. We view regular speed footage at 24 fps, and anything below that looks a little jerky. If you shoot in 50 fps, you can slow the footage down to half speed and stay above 24 fps. You can still slow the footage down if it’s at 24 or 30 fps, and we’re going to show you how.

Option 1: Time Stretch

The Time Stretch function allows you to stretch the clip in your timeline, increasing its length. Trimming the clip tells After Effects which portion of it you want to use.

  1. Right-click on the clip in the timeline and select Time > Time Stretch.
  2. In the dialogue box, you can stretch your clip using 2 different methods; the Stretch Factor and New Duration.
  3. Change the Stretch Factor setting to adjust your clip in percentage terms. Normal speed would be 100, and to slow your clip to half speed, you would change this setting to 200.
  4. Change the Duration setting if you know how long you need the video to be but are not worried about how much the speed has changed. For example, change the number 04.00 to adjust the duration to 4 seconds. This method is super helpful if you need to fit footage into a template.
  5. Click on the Layers panel on the Frame Blend option to choose either Standard Frame Blending or Pixel Motion Frame Blending.

Option 2: Timewarp

Timewarp is an effect that allows you to slow down and speed up a clip without changing its duration. Trimming the clip tells After Effect how long you want it to be in the timeline, and the Timewarp effect compresses or extends the footage beyond your trim points.

  1. Right-click on your clip and choose Effect > Time > Timewarp.
  2. In the Effects Control panel, ensure the Method is set to Pixel Motion.
  3. Change the Speed setting to 25 to create a half-speed effect. The full-speed setting will be 50, so it can be tricky to work out exactly what settings you need for a specific duration.

A plugin that can take the place of the built-in Timewarp effect is Twixtor, which is well worth checking out.

Part 2: How to Use the Twixtor Plugin

Twixtor by RevisionFX is a plugin for After Effects, which can help you create super slow motion footage, even if you’ve not shot at a higher frame rate. Once you’ve installed the plugin, follow these simple steps to create a slow-motion effect.

  1. Add the clip you’re working with to the timeline and trim to the length you want. Make sure your timeline is long enough to include the additional clip length.
  2. Go to Effect > Vision Plugins > Twixtor to add the effect to your clip.
  3. In the Effects Control panel, set your Input Frame Rate to the original frame rate of your video.
  4. Change the Speed setting to your desired percent.
  5. Finally, in the timeline, drag the end of your clip out to the new length.

Part 3: Drone Footage Cinematic Effect Using Slow Motion in After Effects

If you’re fortunate enough to have a Drone for your project, there are some things to consider when filming to help create that cinematic look.

Step 1: Shoot at a Higher Frame Rate

The higher the frames per second your camera films at, the slower you can make your footage before the quality degrades. Always make sure your footage is shot at 50 fps as a minimum. This will allow you to slow down your footage and double the playing time of the clip without losing any quality.

Step 2: Interpret Your Footage

Rather than using Time Effects on your Drone footage, you can Interpret your footage at whatever frame rate you prefer, allowing you to drag it from the browser to the timeline at your chosen speed.

  1. Import your clip by hitting Cmd or Ctrl + I on your keyboard.
  2. Find the clip in the Project Browser and right-click.
  3. Choose Interpret Footage > Main.
  4. Select the Conform To Frame Rate option, change the setting to 24 fps, and hit OK.
  5. Drag your clip to your timeline, and you will see your 60 fps footage has been stretched out to 24fps. You can edit your clip as you would any other media asset, including adding effects, adjustment layers, and keyframe animations.

Step 3: Add Pixel Motion Blur

If you are struggling to make your slow-motion shot smooth, and the Frame Blend options are not doing the trick, you can add the Pixel Motion Blur effect.

  1. Complete the steps above to interpret your footage. You can also apply this effect to slow-motion footage created with Time Remapping, Timewarp, and Time Stretch,
  2. Right-click on your clip in the timeline and go to Effects > Time > Pixel Motion Blur.
  3. Make sure Shutter Control is set to Manual.
  4. Adjust the Shutter Angle and Shutter Sample settings to change the depth of the pixel blur added to your clip.

Step 4: Create the Vertigo Effect

The vertigo effect is a cool effect you can create with moving drone footage, where 2 camera movements appear to be happening simultaneously. The vertigo effect is normally produced in-camera, using a zoom lens and a camera dolly. For drone footage. However, you can achieve this effect in After Effects.

  1. Place the playhead at the end of your clip and create a Scale keyframe.
  2. Move the playhead to the start of your clip and create a second Scale keyframe.
  3. Adjust the Scale of your clip. You should try to create the opposite motion to your camera movements. (Note: if your camera is moving toward something, you should increase the scale of your footage at the start. If the camera is moving away from something, increase the scale at the end).
  4. Play around with the Scale to see how much you want to add until you create a cool vertigo feeling.

After Effects slow-motion tools are comprehensive and robust when used correctly. There is a massive range of styles and looks you can create utilizing the Time Warp and Time Stretch tools. Learn how easy it is to create slow motion in Premiere Pro, DaVinci Resolve, and Final Cut Pro.