Select File
or drag and drop files here
How to Change Video Speed
Upload a video file (MP4, WebM, MOV, AVI, or MKV)
Set the playback speed using the slider — 0.25x for slow motion, 2x for double speed, up to 4x
Click Process and download the result as WebM
Common use cases for changing video speed
- Speed up a long screen recording or tutorial to 2x for faster review
- Create a time-lapse effect from a slow pan or static shot at 4x
- Slow down sports footage to 0.5x to review technique or a key moment
- Speed up a cooking or crafting video to make a short social media clip
- Slow down a music performance video for transcription or learning
- Create dramatic slow-motion effects from standard 30fps footage at 0.25x
Why speed changes require a full re-encode
Unlike muting or trimming — which can copy the video stream directly — changing playback speed requires every single frame to be decoded, re-timed, and re-encoded. The video PTS (presentation timestamp) of each frame must be recalculated, and the audio must be time-stretched and pitch-corrected in sync. This is why speed changes take significantly longer to process than simpler operations. FFmpeg handles all of this correctly in a single pass, but it is computationally intensive, especially when running as WebAssembly in the browser without GPU acceleration.
Key Features
0.25x to 4x Speed Range
Slow down to quarter speed for detailed slow motion, or speed up to 4x for time-lapse style output. The full range is supported in a single pass.
Automatic Pitch Correction
Audio pitch is corrected using FFmpeg's atempo filter chain so voices and music stay at the correct pitch at any speed. No chipmunk effect at 2x, no distortion at 0.5x.
Full Re-Encode with VP9
Output is encoded with VP9 and Opus for good quality and small file size. The re-encode handles both video and audio correctly across the full speed range.
No Upload Required
Processing happens entirely in your browser using FFmpeg compiled to WebAssembly. Files never leave your device.
Complete Privacy
All processing is done locally using FFmpeg WebAssembly running in your browser. No video data is transmitted to any server at any point.
Frequently Asked Questions
Will the audio pitch sound correct at 2x or 0.5x?
Yes. The tool applies FFmpeg's atempo filter chain which corrects audio pitch independently of speed. At 2x the audio is sped up but not pitch-shifted, so voices sound natural rather than high-pitched. The same applies to slow motion.
Why is the output WebM instead of MP4?
The tool uses the VP9 video codec and Opus audio codec, which are bundled in the FFmpeg WASM build used for processing. These codecs produce efficient output and are packaged in a WebM container. WebM is supported in all modern browsers and most video editors.
How long does processing take?
Speed changes require a full re-encode of every frame, so processing time depends on video length and resolution. A 1-minute 1080p video typically takes 1-3 minutes in the browser. FFmpeg WASM is slower than native tools — this is a software limitation.
What speed values are supported?
Any value between 0.25x and 4x in 0.25x increments. The atempo filter has a valid range of 0.5x–2x per stage, so the tool chains multiple stages automatically to support the full range.
Is there a file size limit?
The tool enforces a 500MB limit. Note that processing time scales with file size — very large files may take several minutes to encode.