Why does everyone sound like a chipmunk?

Because the sound is being played faster and pitch rises with speed. Choose to drop the sound, or stretch the audio separately with the tool that preserves pitch.

Why does my slow motion look jerky?

There are no extra frames to show. The clip was filmed at an ordinary frame rate, so slowing it holds each frame on screen longer instead of revealing anything new.

How much faster can it go?

Eight times. Beyond that a viewer cannot follow what is happening, and the result is a flicker rather than a timelapse.

Does the file get smaller when sped up?

Usually, since there is less running time to store — though a fast-moving picture is expensive per second, so the saving is rarely proportional.

Change Video Speed

Play a video faster or slower, sound and all.

Everything runs inside your browser. Your files never leave your device.

Drop your file here

.mp4, .m4v, .mov, .qt, .webm, .mkv, .ts, .mts, .m2ts · they stay on this device

Ask about Change Video Speed

Questions about what this tool does, which option to pick, or what it can and cannot handle.

This is the one part of the site that uses a server. The question you type here is sent to an AI provider to be answered — your files and whatever you put in the tool above are not, and the assistant cannot see them. Answers are generated and can be wrong; the tool itself is not guessing.

About the Change Video Speed

Speeding a video up and slowing it down are the same operation seen from two sides: every frame is given a new moment to appear at, and the file is rebuilt around that new timing.

Speeding up is what turns twenty minutes of a plant growing, a room being painted or a journey being driven into something anybody will actually sit through. Four times and eight times are the useful settings for that, and above eight there is generally nothing left for a viewer to follow. Slowing down is for the opposite case: a fast movement you want to inspect, a moment that went past too quickly to see.

There is an honest limit to slow motion that is worth knowing before you are disappointed. Playing footage at quarter speed does not create any frames that were not recorded. A clip filmed at thirty frames a second becomes, in effect, seven and a half frames a second of new information, held on screen four times as long. It will look stepped, because it is. Genuinely smooth slow motion has to be recorded at a high frame rate in the first place — that is what a phone's slow-motion mode does, and no tool can reconstruct it afterwards.

The sound is the other decision. Speeding audio up raises its pitch, exactly as a record played too fast does, and voices turn comic. That is the honest default here, since it keeps sound and picture together. If the pitch matters more than the sound does, drop the audio and lay a track over the result with Add Audio to Video — or take the sound out first and stretch it properly with Change Audio Speed, which preserves pitch, then bring the two back together.

How to use it

1Add the video.
2Pick a speed. Four times and above is timelapse territory; a half or a quarter is for inspecting a movement.
3Decide whether to carry the sound along or drop it.
4Run it and check the new length reported under the result.

Questions

Why does everyone sound like a chipmunk?: Because the sound is being played faster and pitch rises with speed. Choose to drop the sound, or stretch the audio separately with the tool that preserves pitch.
Why does my slow motion look jerky?: There are no extra frames to show. The clip was filmed at an ordinary frame rate, so slowing it holds each frame on screen longer instead of revealing anything new.
How much faster can it go?: Eight times. Beyond that a viewer cannot follow what is happening, and the result is a flicker rather than a timelapse.
Does the file get smaller when sped up?: Usually, since there is less running time to store — though a fast-moving picture is expensive per second, so the saving is rarely proportional.