Video Speed Changer
Speed up or slow down video clips from 0.25x to 4x with synchronized audio pitch. All encoding happens directly in your browser without uploading files.
MP4, WebM, MOV, MKV, AVI, FLV, 3GP · up to 1 GB
Tips
- The browser downloads a 30 MB media engine once on your first visit, allowing future edits to run completely offline.
- Keep audio pitch correction enabled if you want to avoid chipmunk voices when speeding up or deep voices when slowing down.
- Slowing down footage below its native frame rate duplicates existing frames, so consider recording at higher frame rates for smooth slow motion.
How to use it
- 1 Select or drag and drop a video file from your device.
- 2 Choose your target playback multiplier between 0.25x and 4.0x.
- 3 Toggle pitch correction to keep voice frequencies natural or allow pitch shifts.
- 4 Process the video and save the resulting file once rendering finishes.
What you should know
Changing video speed requires modifying the presentation timestamps (PTS) of video frames and resampling audio streams. When speeding up footage to condense long screen recordings or timelapses, frame intervals shorten and excess frames may be dropped to match target frame rates like 30 or 60 fps. Slowing down video expands frame intervals, which creates choppy playback unless source files were recorded at high framerates like 60 or 120 fps. Audio presents an additional challenge: simple speed changes alter pitch unless processed through time-stretching algorithms that maintain natural vocal frequencies without distortion.
This tool alters playback speed between 0.25x and 4x while re-encoding both video and audio streams entirely client-side. You can preserve the original voice pitch during speed adjustments or let the pitch scale naturally with playback tempo. The WebAssembly engine processes your file locally using your computer hardware, meaning processing time depends on clip duration, resolution, and selected bitrate. Because processing runs in a single browser thread, high-resolution 4K files or lengthy videos will take several times their actual playback duration to encode, and complex container metadata or extra subtitle tracks are discarded.
Frequently asked questions
Will changing the video speed degrade image quality?
The tool re-encodes video frames at high bitrates to match the new speed, which preserves visible visual clarity while changing frame timing.
Why does rendering take longer than the original clip duration?
Video processing runs locally through WebAssembly inside a single browser thread, so software re-encoding requires substantial CPU power for high-resolution footage.
Can I adjust the speed of audio tracks without altering the pitch?
Yes, the built-in time-stretching filter automatically compensates for speed increases or decreases, preserving standard vocal pitch across the 0.25x to 4x range.
Guides
Articles and format references related to this tool.
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