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Read guide →Change Video Speed
Speed up or slow down a video from a quarter speed to four times, retiming the audio alongside the picture.
Drop a video here or click to browse
MP4, WebM, MOV, AVI — processed locally and never uploaded.
Reviewed 2026-08-15
Free Change Video Speed – how it works
Video timing is changed with the setpts filter, which rewrites each frame's presentation timestamp. Audio is handled separately with atempo, which stretches or compresses the waveform in time while leaving pitch broadly intact, so sped-up speech does not turn into a chipmunk.
Six presets are available: 0.25x, 0.5x, 0.75x, 1.5x, 2x, and 4x. Slowing a clip down does not create new frames, so at 0.25x you are seeing each original frame held four times as long. Footage shot at a high frame rate slows down much more convincingly than standard 30 fps video.
If the source has no audio, the audio filter is skipped entirely rather than failing or emitting a silent track.
How to use Change Video Speed online
- Add the video. Drop in the clip you want to retime.
- Pick a speed. Values above 1 shorten the clip, values below 1 lengthen it. Two times is the usual choice for trimming dead time out of a demo; 0.5x is the common pick for examining fast motion.
- Render and watch it back. Run the change and play the result. Listen to the audio too, since heavy speed changes are more audible than they are visible.
When to use it
- Halve the running time of a long screen demo so it fits an attention span.
- Slow a fast interaction down enough to see what the interface actually did.
- Speed a timelapse-style recording up to 4x for a summary clip.
- Fit a clip to a platform duration cap without cutting content out of it.
Known limitations
- Slowing down repeats existing frames rather than interpolating new ones, so heavy slow motion on ordinary footage looks stuttery.
- The audio retime keeps pitch roughly stable but is not transparent. At 4x or 0.25x, speech develops audible artefacts.
- Everything is bounded by the memory one browser tab can claim. Clips under about 30 seconds are comfortable; multi-minute or 4K footage often stalls or fails with an out-of-memory error.
Frequently asked questions
Does the audio pitch change when I speed up the video?
Not appreciably. Audio is retimed with atempo, which changes duration while holding pitch, rather than simply resampling. Extreme settings still introduce artefacts, but voices stay recognisable.
Why does slow motion look choppy?
There are no extra frames to show. At 0.5x each original frame is held twice as long, so 30 fps footage effectively plays at 15. Filming at a higher frame rate in the first place is the only real fix.
Is my video uploaded to a server?
No. FFmpeg is compiled to WebAssembly and runs inside the page, so the file is read from your disk into the tab's own memory. Nothing about the video is sent to opentools.
Can I ramp the speed gradually instead of applying one rate?
Yes, but not here. The Video Editor supports a speed curve per clip with easing, so a clip can start at normal speed and accelerate.
Why does the first render take longer?
The FFmpeg WebAssembly build is about 31 MB and has to download before the first job can start. The browser caches it afterwards, so later visits skip that step and begin encoding almost immediately.
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