How to Change a Digital Video Clip’s Speed with Time Stretch
The duration of your DSLR video clip represents the length of time it plays from start to finish. In the linear world, you alter the length by lopping off frames. For example, instead of the subject walking into the frame, through a long passage and out of the frame, you can trim the point when she’s walking and out of the frame.
The alternative to that method is to change the speed of the clip to make the subject move faster through the scene or in slow motion, if you choose.
To create a fast- or slow-motion effect, you can change clip speed. Sometimes you can make the scene move slightly faster, or slower, to fit into a specific place, for example, if you’re making a music video.
Other times, you may want to show a quick passage of time. Notice how reality shows use this effect by speeding up an establishing shot to show a passage of time. Other times, you may do the opposite and slow the scene down to let the audience savor details they may have missed at normal speed.
To slow down a clip that has another clip on its right in the Expert view timeline, drag it to an empty track or to the end of the movie. This way, you can stretch it without bumping into an adjacent clip.
Follow these steps to alter the time of your clip:
Select the desired clip in the timeline.
Just click the clip to highlight it. Choose Clip→Time Stretch. You can also click the Tools panel on the Action bar and choose Time Stretch.
Stretch the clip (or contract).
In the Time Stretch dialog, type a percentage for Speed. Remember, 100 percent is the baseline, so values less than 100 percent slow the clip down, whereas higher values speed it up. That means at 50 percent the clip plays at half the speed. At 200 percent, it’s twice as fast as normal.
Decide if you want to maintain pitch.
Normally when you change the video speed, the audio changes too. Sometimes that’s an acceptable effect, but most of the time, you want to shy away from changing the speed of spoken dialogue. When it comes to ambient noise, speeding up a clip can give you that fast-forward sound. In order to eliminate that, check Maintain Audio Pitch in the dialog so the audio sounds normal.
Remember the clip changes size in the timeline.
When you slow the clip down by 50 percent, the clip represents that much more space in the timeline. Make sure that you move the clips to the right to accommodate the size before you change the clip speed.
Preview your changes.
After you make your adjustments, watch the clip and click OK if you're satisfied.
Sometimes you want to alter the speed of more than one clip. If the duration is the same, you can apply the Time Stretch function to multiple clips.
Here are several ways you can select multiple clips:
Shift+click each clip.
Drag a marquee around the selected clips.
Select all the clips in the timeline by clicking the timeline and selecting Edit→Select All.