Editing the speed of a video clip in After Effects primarily involves adjusting its duration relative to its original playback time, with one straightforward method being the Time Stretch feature.
Adjusting Clip Speed Using Time Stretch
The Time Stretch feature in After Effects allows you to quickly speed up or slow down a video clip by changing its Stretch Factor. This method is effective for making global speed adjustments to a single layer.
Step-by-Step Guide to Using Time Stretch
Follow these steps to modify the speed of your video clip:
- Locate Your Clip: In your After Effects timeline, find the video layer you wish to edit.
- Access Time Stretch:
- Right-click on the video clip layer in the timeline.
- From the context menu, navigate to Time.
- Select Time Stretch...
- Adjust the Stretch Factor:
- A "Time Stretch" dialog box will appear.
- In this dialog box, you will see a field for Stretch Factor (represented as a percentage).
- 100% represents the clip's original speed and duration.
- To speed up the video, decrease the percentage value. For example, setting it to 50% will make the clip play twice as fast.
- To slow down the video, increase the percentage value. For example, setting it to 200% will make the clip play at half its original speed.
- As you adjust the Stretch Factor, the new duration of the clip will automatically update.
- Confirm: Click OK to apply the changes. The clip's layer in the timeline will visibly lengthen or shorten to reflect the new duration and speed.
Understanding the Stretch Factor
The Stretch Factor directly correlates to how much the original duration is "stretched" or "compressed."
| Stretch Factor (%) | Effect on Speed | Effect on Duration | Example Result |
|---|---|---|---|
| 100% | Original Speed | Original Duration | 5-second clip remains 5 seconds |
| < 100% | Speeds Up | Decreases Duration | 50% makes a 5-second clip play in 2.5 seconds |
| > 100% | Slows Down | Increases Duration | 200% makes a 5-second clip play in 10 seconds |
Practical Tips for Time Stretch
- Global Adjustment: Time Stretch is ideal for applying a uniform speed change across an entire video layer.
- Simplicity: It's one of the simplest methods for quick speed adjustments.
- Frame Blending: For significant speed changes, especially slowing down footage, consider enabling Frame Blending or Pixel Motion on the layer to achieve smoother playback and avoid choppy results. You can access these options by right-clicking the layer > Frame Blending.
- Limitations: While effective, Time Stretch doesn't offer the granular control of keyframe-based speed ramps or time-remapping, which allow for variable speed changes within a single clip.
