Video Speed Changer
Upload a video, pick a speed from 0.25x to 4x using the preset buttons or a custom number input, and export a new file with both the picture and the audio re-timed to match. Choose MP4 or WebM as the output container; the tool automatically picks whichever your browser can encode. Everything runs on-device using the browser's native WebCodecs and Web Audio APIs, no upload involved.
Reviewed by Vincenzo Manto, Founder & Lead Developer · Last updated October 11, 2026
How it works
- 1
Upload a video file and let it load in the player.
- 2
Pick a speed preset (0.5x-3x) or type a custom value between 0.25x and 4x.
- 3
Check the estimated result duration shown below the player.
- 4
Pick MP4 or WebM and export. The tool re-times both the video frames and the audio to the new speed.
Re-timing frames and audio, not just relabeling them
Rather than rely on a container-level playback-rate flag that most players and devices ignore, this tool decodes every video frame and divides its timestamp and duration by your chosen speed factor before re-encoding, and separately resamples the audio track through an OfflineAudioContext at the same factor, so the exported file plays at the new speed on any device without special support.
An honest tradeoff on audio pitch
Changing playback speed without altering pitch requires a time-stretching algorithm (a phase vocoder), a substantial piece of DSP that's out of scope for a from-scratch, in-browser tool. Instead, this tool resamples audio the same way adjusting the speed knob on a tape deck or turntable would: pitch rises with speed and falls with slowdown. It's a well-understood, honest tradeoff rather than a silently broken pitch-preservation claim.
Frequently asked questions
Does the audio pitch change when I speed up or slow down a video?
Yes, and this is intentional and disclosed rather than hidden: the tool resamples the audio using the Web Audio API at the chosen speed factor, which shifts pitch the same way an old tape or vinyl record does when played faster or slower - faster speeds raise the pitch, slower speeds lower it. Pitch-preserving time-stretching is a much more complex algorithm (a phase vocoder) that isn't implemented here.
What's the fastest and slowest speed I can choose?
Anywhere from 0.25x (quarter speed, 4x longer) to 4x (four times faster, a quarter of the original length). Use the preset buttons for common values or the number input for anything in between.
Does this happen on a server?
No. Decoding, re-timing, and re-encoding all happen entirely client-side in your browser tab using WebCodecs and Web Audio, so the video is never uploaded anywhere.
Why is the video re-encoded instead of just changed in metadata?
Most players ignore a simple 'play faster' flag in a file's metadata, and there's no reliable cross-player way to tag a different frame rate for only part of a file. Re-encoding at the new timestamps guarantees the sped-up or slowed-down result plays correctly everywhere.
What if my browser doesn't support MP4 or WebM encoding?
The tool checks what your browser can actually encode before you export and only offers the formats that will work. If neither is available (a very old browser), it tells you plainly. Try a recent version of Chrome, Edge, Firefox, or Safari.
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