Change Video Speed
Speed a clip up or stretch it out, anywhere from a quarter speed to four times. The picture is copied rather than re-encoded, so nothing is lost on the way through, and the preview plays at the exact speed and pitch you have chosen before you export anything.
Why the picture survives and the sound is rebuilt
A video frame carries a picture and a presentation time. Retiming a clip changes only the second of those — the pixels of frame 400 are the same pixels whether the clip runs at 1× or 4×. So this tool never decodes them: it reads the encoded packets, divides every timestamp by the speed you picked, and writes them back out. The frames you download are bit-for-bit the frames you brought, which is why this finishes in seconds on a clip that the crop and resize tools would spend minutes on — those change the shape of a picture, and there is no shortcut for that.
Audio has no equivalent. Samples run at a fixed rate — 48,000 a second, say — so a soundtrack that plays in half the time has to contain half as many of them, and no amount of timestamp arithmetic produces that. The samples have to be rebuilt. Doing it the obvious way, by reading every other one, is what makes a sped-up voice sound like a chipmunk: the waveform's periods shrink along with the clip, and pitch is period. The default here instead cuts the audio into overlapping windows and lays them back down closer together, matching each one against the waveform already written so the seams add rather than cancel. The clip gets shorter; the periods inside each window never change; the voice stays where it was.
The one thing retiming cannot do is invent frames. Slowing footage down spreads the frames you have across more time, so a 30 fps clip at quarter speed is genuinely a 7.5 fps clip — the tool prints that number before you run it rather than after. If you need smooth slow motion, it has to come from the camera; check what your platform accepts on the frames calculator first.
Frequently asked questions
How do I speed up or slow down a video?
Drop the file in, pick a speed between 0.25× to 4× — or drag the slider to anything in between — and export. The preview plays at the speed you have chosen, with the pitch setting you have chosen, so you can hear the result before you commit to it.
Will the voices sound like chipmunks?
Only if you ask them to. The default keeps the pitch where it is, the way an editor does when it retimes a clip: the soundtrack is cut into overlapping windows and those windows are laid back down closer together, so the clip gets shorter while every waveform inside it keeps its original length. If you actually want the tape-speed effect, there is a setting for that too — and a third that drops the audio entirely.
Does this re-encode my video and lose quality?
Almost never. A speed change is a timestamp change: the frames themselves are identical whether a clip plays at 1× or 4×, so this tool copies the encoded picture straight through and only rewrites the timing. Your output frames are bit-for-bit the ones you started with. That holds for H.264, HEVC, VP9, VP8, AV1 and ProRes — everything a phone, camera or screen recorder produces. Only an unusual codec that no common container can carry has to be re-encoded, and the tool says so before you start.
Why is slow motion choppy?
Because retiming spaces out the frames you already have; it does not invent new ones. A 30 fps clip at quarter speed is a 7.5 fps clip — every original frame is still there, just held four times as long. That is what every non-AI speed tool does, and the tool warns you with the exact resulting frame rate before the run. Smooth slow motion comes from footage shot at a high frame rate in the first place.
How long does it take?
Dropping the audio makes it a pure stream copy — seconds, regardless of whether the clip is thirty seconds or an hour. Keeping the audio adds the time it takes to rebuild the soundtrack, which runs at a few hundred times realtime, so a five-minute clip spends a second or two on it. Neither case re-encodes a single frame of picture.
Does this upload my video anywhere?
No. The file is read from disk and retimed inside this browser tab — there is no server, no queue, no account and no watermark. MP4, MOV, MKV and WebM go in, up to 2 GB.