Video Speed
Drag the speed control and watch the preview change right away — that's just the browser's own playback, nothing is processed yet. Once you decide, the video is re-encoded at the chosen speed, and the audio follows without turning into a chipmunk: the original pitch is preserved. All in your browser, with no upload.
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How it works
The video uses the setpts=PTS/speed filter, but that alone only retimes the frames — without pinning a higher output rate, the codec keeps the original frame rate and drops whatever doesn't fit the grid, losing motion instead of speeding it up. So the tool also sets an output rate of 60fps times the chosen speed: it covers the real rate of most videos, and when it doesn't, the effect is a duplicated frame, never a lost one. Audio is a different story: ffmpeg's atempo filter only accepts a factor between 0.5 and 2.0 at a time — asking for 4x or 0.25x directly fails. The tool decomposes the speed into a chain of atempo stages (for example, 4x becomes two atempo=2 in sequence) whose product gives the final factor, keeping the pitch correct at any speed within the 0.25x-4x range.
- From 0.25x (slow motion) to 4x (sped up)
- Instant preview with the player, before processing
- Optional audio, pitch preserved (no chipmunk effect)
- Before/after size comparison