0.25x–4x video speed with audio kept in sync (atempo) — slow-mo & timelapse.

How to use

1. Drop a video → pick a speed (0.25–4x).
2. Choose keep-audio or mute.
3. Process → download the retimed MP4.

About this tool

Slow-motion sports clips, 2x lecture speed, 10x timelapse B-roll — one slider handles it all. The FFmpeg engine adjusts video timing with setpts while the audio runs through an atempo chain that preserves pitch, so voices never go chipmunk. Everything is processed on your device through WebAssembly. Your file never leaves this page — processing runs in your browser via WebAssembly; nothing is uploaded and the file is dropped from memory when you close the tab.

FAQ

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