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Pick a speed between a quarter and four times normal and watch the preview play at that pace straight away. When it feels right, save it: the new timing, and the matching audio, are written into a fresh MP4.
Processing locally on your device
Overview
Changing a video’s speed means changing how long each frame is shown. Eight presets cover the common choices — 0.25×, 0.5×, 0.75×, 1.25×, 1.5×, 2×, 3× and 4× — and a slider sets any value in between in steps of 0.05. The player previews the chosen speed instantly, using your browser’s own playback-rate control, and the tool shows the original length next to the new one, so you know a 3-minute clip at 1.5× will run 2 minutes.
Speeding up drops frames. The output keeps the source frame rate rather than packing in more frames per second, so a 30 fps clip at 2× is still 30 fps and plays smoothly on every device. Slowing down does the opposite: each frame is held for longer, and frames are repeated to keep the original frame rate. That works well for footage shot at 60, 120 or 240 fps, where there are plenty of real frames to stretch. A normal 30 fps clip slowed to 0.25× will look steppy, because the tool doesn’t invent in-between frames.
Sound is handled separately. With Keep audio on, the track is retimed with FFmpeg’s atempo filter, which changes speed without changing pitch, so voices at 1.5× sound quicker but not like chipmunks, and slowed speech keeps a natural tone. Speeds beyond the filter’s single-step range are reached by chaining it. Turn Keep audio off to drop the soundtrack entirely, which is common for slow-motion clips you plan to set to music. Video is saved as H.264 MP4 at CRF 21 and audio as AAC at 160 kbps.
The work happens in your browser with FFmpeg 5.1 compiled to WebAssembly, a one-time download of about 31 MB that is then cached. Since every frame is re-encoded, processing time grows with the length of the output: a slowed-down clip gets longer and so takes longer, while a sped-up clip has fewer frames to encode and finishes faster.
| Speed | New length | Good for |
|---|---|---|
| 0.25× | 4:00 | Dramatic slow motion (120+ fps sources) |
| 0.5× | 2:00 | Sports technique, action moments |
| 1.5× | 0:40 | Tutorials and talking heads |
| 2× | 0:30 | Skipping slow sections, comic effect |
| 4× | 0:15 | Timelapse-style processes |
Drop a video into the speed changer.
Click a preset such as 0.5× or 2×, or drag the slider to any speed from 0.25× to 4×.
Play the preview to check the pace.
Choose whether to keep the audio.
Click Change speed and download the MP4.
Use cases
Turn a slow process — a sunset, a build, a drawing — into something watchable at 3× or 4×, without needing a dedicated timelapse app.
Phones that shoot 120 or 240 fps capture real slow motion. Slow it to 0.25× here and every frame is a genuine one, so movement stays smooth.
Speed a screen recording to 1.25× or 1.5× so it gets to the point, while the pitch-preserved narration still sounds like you.
A quick burst of 2× or a dramatic 0.5× slowdown adds punch to pets, pranks and sports clips for social posts.
Pro tips
Answers to common questions about the speed changer.
No. With Keep audio on, the sound is retimed with a pitch-preserving filter, so voices and music keep their original pitch at any speed. Very large changes can sound slightly processed.
Slowing down holds and repeats existing frames; the tool doesn't generate new in-between frames. Footage shot at 30 fps has few frames to stretch, so 0.25× looks steppy. High-frame-rate footage slows down much more smoothly.
The same as your source. Speeding up drops frames instead of raising the frame rate, and slowing down repeats frames, so the file plays smoothly everywhere.
Not in one pass. For larger changes you can run the result through the tool again, for example 4× twice for 16×.
It depends on the output length and resolution, because every frame is encoded again in the browser. Sped-up videos are shorter and finish faster; slowed-down videos are longer and take proportionally more time.
No. ToolEnhancer processes files on your own device inside the browser. They are never sent to, stored on or seen by our servers.
Yes. The speed changer is free to use with no sign-up, no watermarks and no daily limits.