No upload, 100% local, no account

Change video speed

Speed up a tutorial or slow down a clip for detail, the soundtrack follows without the chipmunk effect. Everything runs in your browser; your file never leaves your device.

How Video speed works

Video speed changes the playback rate of a clip from 0.25x to 4x directly in your browser, using ffmpeg compiled to WebAssembly. The video stream is rescaled with the setpts filter (a straight timestamp rewrite, so there is no frame blending or quality loss beyond the codec re-encode), and the audio track is time-stretched with the same atempo filter chain audio-speed uses, so the soundtrack follows the new pace without a chipmunk or slow-motion voice.

Speeds outside the 0.5x-2x range that a single atempo stage accepts are reached by chaining multiple stages automatically; you just pick a value from 0.25x to 4x. Nothing is uploaded: the file is read, processed and re-encoded on your own device.

Written by Bastien Sulyan

How to use Video speed, step by step

  1. Drop or select the video file you want to speed up or slow down.
  2. Set the speed with the slider or a preset button, from 0.25x to 4x.
  3. Click Start. ffmpeg rescales the video timing and time-stretches the audio locally.
  4. Preview the result and download it once processing finishes.

Common use cases

  • Speeding up a screen-recording tutorial to 1.5x or 2x so it is quicker to watch.
  • Slowing a sports or dance clip to 0.5x to study the technique frame by frame.
  • Shortening a long clip to fit a social-media time limit without cutting content.
  • Matching a video clip length to a fixed music track duration.

Frequently asked questions

Is my video uploaded anywhere to change its speed?

No. ffmpeg compiled to WebAssembly rescales the video and audio timing inside your browser tab. The file is read into memory on your device, processed there, and the sped-up or slowed-down result is offered as a local download. Open your browser DevTools Network tab while running the tool and you will see no request carrying your video.

Does the audio pitch change along with the speed?

No. The audio track goes through the same atempo time-stretch that audio-speed uses, which changes duration without shifting pitch. A voice at 2x sounds faster but not higher-pitched; at 0.5x it sounds slower but not deeper. If you want a genuine pitch change, the audio-pitch tool does that instead, independently of speed.

Why does the video stream use a different technique from the audio stream?

Video timing is a straight timestamp rewrite (setpts=PTS/speed): each frame simply gets a new presentation time, so no frames are invented or dropped for a moderate speed change. Audio cannot work that way, since resampling it naively would shift pitch, so it uses the atempo time-stretch filter chain instead, the same one audio-speed relies on.

Does changing the speed re-encode the whole video?

Yes. Both the video and audio streams are re-encoded, because their timing is rewritten. The output codec is chosen from your output file extension (H.264 for MP4/MOV/MKV, VP8 for WebM), so the result stays playable everywhere.

What is the largest file I can speed up or slow down?

Up to 500 MB, the same ceiling as the other one-shot ffmpeg video tools on this site (rotate, crop, trim). On a memory-constrained mobile device the limit is lowered automatically to protect the tab from running out of memory.

Does video speed work offline?

Mostly, yes. The speed change itself always runs on your device, so your video never leaves your machine. The one caveat: ffmpeg's engine is a sizeable download fetched from this site the first time you use any ffmpeg-based tool. Once that download and the page have both completed, you can disconnect from the network and the speed change still works.