Change How Long a Video Lasts
Type the length you want and get exactly that. An 8-second clip becomes a 40-second slow-motion shot — audio stays in sync, nothing gets cropped.
Select a video to retime
MP4 · MOV · WEBM · MKV · AVI — up to 1.00 GB
Your video never leaves your device — everything runs in this tab.
Silent retimes skip encoding entirely and finish in seconds.
Need this in a script? Retime over the API.
Set the Duration, Not a Guess
Most speed tools make you work out the multiplier yourself, then hope the result lands near the length you needed. This one works the other way round: you say "make it 40 seconds" and the speed is calculated from your clip's real duration, so the finished file is that length. Perfect for filling a fixed ad slot, stretching a short clip over a voiceover, or turning a quick action shot into proper slow motion.
Exact Target Length
Enter a duration in seconds and the output matches it, whatever the source length happens to be.
Instant When Silent
A clip with no sound is retimed by rewriting frame timing alone — nothing is re-encoded, so it is lossless and finishes in seconds however big the file is.
Audio Stays in Sync
Sound is stretched to the new length with its pitch intact, automatically. There is nothing to configure.
How to Change a Video's Duration
Upload Your Clip
Drop in an MP4, MOV, WEBM, MKV or AVI. Its current length is read straight away.
Enter the New Length
Type the number of seconds you want — or switch to speed mode and pick a multiplier like 0.2×.
Retime and Download
Press Retime and save the finished video. Everything else is decided for you.
Frequently Asked Questions
Can I turn an 8-second video into a 40-second one?
Yes — that is exactly what this tool is for. Upload the clip, type 40, and it comes back 40 seconds long, playing at one fifth of the original speed. You can stretch a video up to 50 times its original length, or shorten it by the same factor.
Will the slow-motion look choppy?
Each original frame is held on screen longer, which keeps every frame perfectly sharp and shows the source's own frame rate — the same thing a video editor does when you slow a clip down. The output is written at a normal frame rate, so it plays smoothly everywhere.
What happens to the sound?
It is tempo-stretched to the new length with its pitch preserved, so speech stays understandable and nothing drifts out of sync. This happens automatically — there is no audio setting to get wrong.
Does retiming reduce the quality?
If the clip has no audio track, nothing is re-encoded at all — only the frame timestamps change, so the picture is bit-for-bit the original. When there is sound to keep in sync the video is re-encoded at a near-visually-lossless quality setting.
Is my video uploaded anywhere?
No. The whole retime runs inside your browser tab, so the file never leaves your device. There is also an API endpoint if you need to do this from a script or on a server.