Speed Ramping

Speed Control Overview

VideoBuff's speed control lets you adjust playback speed from 0.1x (slow motion at one-tenth speed) to 10x (time-lapse style). Beyond simple speed changes, it supports smooth speed ramping with easing curves for gradual acceleration and deceleration effects.

You can highlight action scenes with slow motion, compress long work sessions into time-lapse sequences, and control the tempo and pacing of your video. A pitch preservation feature maintains natural audio pitch even when speed is changed.

Basic Speed Change

To change speed, select a clip on the timeline and adjust the rate in the Speed section of the inspector panel. Drag the slider or enter a numeric value directly to set the speed.

Changing the speed automatically adjusts the clip's length — 2x speed halves the length, while 0.5x speed doubles it. Speed changes are reflected in the preview in real time, letting you find the right speed as you adjust.

The speed value is displayed on the clip in the timeline, so you can see at a glance which clips have speed changes applied.

Speed Ramping with Easing

Enabling the easing toggle makes speed changes occur along a smooth curve rather than abruptly. Ramp duration can be set from 100ms to 3000ms, defining how long the transition takes from the original speed to the target speed.

For example, setting 500ms of easing for a 1x to 0.3x slow-motion transition creates a cinematic half-second deceleration effect. The easing curve is calculated with bezier interpolation, producing organic rather than mechanical speed changes.

This is especially effective for highlights in action or sports footage.

Range-Based Speed Change

You can apply a speed change to only a specific portion of a clip rather than the entire clip. The range start and end positions are specified as percentages — for example, applying slow motion only to the 30% to 60% portion of the clip.

This lets you create sections of normal speed and slow motion within the same clip. Parts outside the range play back at the original speed.

This feature is useful for adding speed variation without splitting the clip, keeping the timeline simple while enabling advanced speed effects.

Preserve Pitch

Changing speed normally also changes the pitch of the audio. At 2x speed, the pitch rises, and at 0.5x speed, it drops.

Enabling the preserve pitch toggle maintains the original audio pitch regardless of speed changes. This is particularly important when adjusting the speed of clips containing narration or interview audio, preventing unnatural pitch shifts.

Pitch preservation is performed in real time using Web Audio API processing, with the same effect applied in both preview and export.

Technical Note: Speed Ramping Implementation

Easing curves are implemented through frame timing calculations using bezier interpolation. The display timing of each frame is dynamically determined based on the speed curve, producing smooth acceleration and deceleration.

Pitch preservation combines the Web Audio API's playbackRate property with detune functionality to counteract the pitch shift caused by speed changes. During decoding, the WebCodecs API's VideoDecoder outputs frames, and frame skipping or repetition is performed based on calculated timing.

This enables efficient speed ramp processing with hardware acceleration.