Video Speed Changer
Speed up or slow down a video from 0.25x to 4x, keeping the audio in sync and at its natural pitch.
Tool guide
What this tool does
Video Speed Changer re-times your video with FFmpeg’s setpts filter and stretches the audio with the atempo filter, which changes tempo without the chipmunk effect. Use presets for slow motion or timelapse, or enter any multiplier between 0.25 and 4.
A tutorial that drags, a long screen recording that would be clearer at double speed, or an action shot you want to show in slow motion all need the playback speed baked into the file, not just changed in your player. Many sharing platforms do not offer speed controls at all.
The tool uses FFmpeg compiled to WebAssembly. The video timestamps are divided by your multiplier (setpts=PTS/speed), so 2x halves the duration and 0.5x doubles it, and the result is re-encoded to H.264 MP4. Audio is processed with a chain of atempo filters, which time-stretch the sound while keeping its pitch, so voices still sound natural. Frames are not invented for slow motion: a 30 fps clip at 0.5x plays its real frames for twice as long. Everything happens on your device.
How to use Video Speed Changer
- Drop one or more videos onto the upload area, or click to browse.
- Pick a preset (0.5x, 1.5x, 2x, 4x) or type a Speed multiplier between 0.25 and 4.
- Choose whether to keep the audio with preserved pitch or remove it.
- Choose Quality; Standard (CRF 22) suits most uses.
- Click Change speed and follow the progress bar.
- Preview the result and download it.
Tips for better results
- 1.25x to 1.5x makes talking-head tutorials feel brisker without hurting comprehension.
- For dramatic slow motion, start from high-frame-rate footage (60, 120 or 240 fps); normal 30 fps clips will look choppy below 0.5x.
- Remove the audio for timelapses; time-stretched sound at 4x is rarely useful.
- Trim the clip first so you only re-encode the part you need.
Common use cases
- Turning a 20-minute screen recording into a 5-minute timelapse.
- Slowing down a sports swing or a dance move for analysis.
- Speeding up a recipe or crafting video for social media.
- Making a lecture recording faster for revision.
Common mistakes to avoid
- Expecting smooth slow motion from 24 or 30 fps footage; the tool repeats real frames rather than generating new ones.
- Using extreme speeds with speech; above 2x voices become hard to follow even with pitch preserved.
- Forgetting that the output is always re-encoded; keep the original file.
Frequently asked questions
Will the audio sound high-pitched when sped up?
No. The atempo filter changes the tempo of the audio without changing its pitch, so speech sounds natural at moderate speeds such as 1.5x or 0.75x.
How is the new duration calculated?
New duration = original duration ÷ speed. A 60-second clip at 2x becomes 30 seconds; at 0.5x it becomes 120 seconds.
Why is processing slower than playback?
Changing speed requires decoding and re-encoding every frame, and the browser engine runs on a single CPU thread. Shorter or lower-resolution clips finish much faster.
Is my video uploaded?
No. The FFmpeg engine is downloaded once from the jsDelivr CDN; the video is processed in your browser.
Feedback & suggestions
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