How to Speed Up or Slow Down a Video

When to change clip speed

Speed change is one of the most expressive tools in an editor's kit. Slow motion draws out a moment, giving the viewer time to take in detail that would otherwise flash past in an instant - a water balloon bursting, a dancer landing a jump, a car drifting through a corner. Fast motion compresses long, repetitive, or time-consuming processes into a few engaging seconds, a technique used in everything from cooking videos to construction montages.

Beyond aesthetics, speed is also a practical editing tool. A clip that's slightly too short to fill a gap in your timeline can be stretched to fit. A clip that runs too long can be sped up to compress it without losing content. When combined with keyframe animation, gradual speed ramps - where the clip accelerates or decelerates smoothly - create a high-end cinematic look.

How slow motion works: the basics of frame rate

Understanding slow motion requires understanding frame rate. Standard video is shot and played back at 24, 25, or 30 frames per second (fps). Your eye perceives motion as smooth at these rates because the frames update faster than your visual system can detect individual images.

Slow motion is created by shooting at a higher frame rate - 60, 120, or 240 fps - and then playing that footage back at the standard 24 or 30 fps. Because more frames are captured per second than are displayed, each source frame is shown for longer, which stretches time. Footage shot at 120 fps played back at 30 fps is 4x slow motion - each second of action becomes four seconds on screen.

If your camera only shoots at 30 fps and you apply slow motion in post, the editor must manufacture missing frames by duplicating or interpolating between existing ones. This produces a characteristic "blurry" slow motion rather than the smooth, crisp slow motion of true high-frame-rate footage. It can still be effective for mild slowdowns (0.5x), but breaks down visually below about 0.25x on 30 fps source material.

Slowing down a clip in LuxOpus

Select a clip in the timeline, then open the Inspector panel on the right side. Go to the Properties tab and find the Speed slider. Dragging it to the left reduces speed - 0.5x is half speed (slow motion), 0.25x is quarter speed.

When you reduce a clip's speed, it gets longer in the timeline. A 10-second clip at 0.5x speed occupies 20 seconds. LuxOpus adjusts the clip's length automatically; you don't need to manually extend it. If the slowed clip now overlaps a neighbouring clip, you'll need to move the following clips to the right to make room, or use ripple delete to rearrange the sequence.

The audio pitch is automatically adjusted when you change speed. At 0.5x speed, audio plays at half pitch, which on dialogue produces the familiar deep slow-motion voice effect. If you want to remove or replace the audio on a slowed clip, mute the track or delete the audio clip separately.

Speeding up a clip: fast forward and time-lapses

Increasing a clip's speed works the same way in reverse. In the Inspector's Properties tab, drag the Speed slider to the right. Values above 1x speed the clip up - 2x is double speed, 4x is quadruple speed.

Sped-up footage is often used for B-roll: the secondary footage that plays while a voiceover continues. A time-lapse of clouds moving, a city street filling up over an afternoon, or a fast-cut montage of someone building or cooking all benefit from the 2x–4x range. The motion looks energetic and purposeful.

Fast-forwarded speech sounds comical at 2x and incomprehensible above that. If you're speeding up a clip that contains dialogue you want to keep, consider keeping the speed below 1.5x, or removing the audio and replacing it with music or a separate voiceover track.

What happens to audio when you change speed

When you change a clip's speed, the audio changes too. Slowing down stretches the audio waveform, lowering the pitch. Speeding up compresses it, raising the pitch. This is physically accurate - it's the same phenomenon you hear when a record plays too fast or too slow.

For music and ambient sound, this is often desirable or at least acceptable. For dialogue, it sounds unnatural. The standard professional solution is to separate the audio from the video, keep the audio at normal speed, and only change the speed of the video portion. In LuxOpus, you can do this by placing the audio on a separate audio track, unlinking the clip from the video, and applying speed change to the video clip only.

For slow motion sequences in action footage, most editors mute the original audio and replace it with music, because slow-motion audio is rarely usable - it picks up camera handling noise, wind, and mechanical sounds in an exaggerated way.

Creative uses: speed ramps and transitions

A speed ramp is a gradual transition between different playback speeds within a single clip - for example, starting at 1x, slowing to 0.25x at the moment of impact, then returning to 1x. This technique is used extensively in action sports, music videos, and film trailers because it directs the viewer's attention to the most important moment.

In LuxOpus, you can approximate a speed ramp by cutting a single clip into three pieces - before, during, and after the key moment - and setting different speeds on each piece. Trim the boundaries between pieces carefully so the motion is continuous across the cuts. It takes a few minutes but produces a convincing result.

Speed changes also work well as a substitute for transitions. Rather than dissolving between two clips, try ending a clip with a fast acceleration (2x–4x on the last half-second) and beginning the next clip at slow motion (0.25x for the first second). The energy contrast gives the cut a sharp, intentional feel without relying on a dissolve effect.