Why does the audio pitch change?

We set the video element's playbackRate directly, which speeds up or slows down both video and audio together. At 2× audio is one octave higher; at 0.5× it's one octave lower. Browsers don't expose formant-preserving time-stretching to web pages.

Why does encoding take as long as the resulting video?

We capture in real time — if your output is 30 seconds at 2× from a 60-second source, encoding takes ~30 seconds. Native tools like ffmpeg can do this much faster with the setpts filter.

Why is the output WebM?

MediaRecorder in Chrome and Firefox encodes to WebM (VP9/VP8 + Opus). Safari may produce MP4. The format may differ from your input.

Can I get true slow-motion with smooth frames?

Not with this approach — we're just re-recording at a different rate, not interpolating frames. For buttery slow-mo you need optical-flow frame interpolation, which native tools (Premiere, Twixtor) do better.

Is the file uploaded?

No. The video plays locally and is captured via MediaRecorder. DevTools → Network will show zero uploads.

What if captureStream isn't supported?

We fall back to drawing frames onto a canvas and capturing that, in which case the output is video-only (no audio). The UI tells you which method was used.

Change Video Speed

Speed up or slow down a video in your browser (0.5×–2×).

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See how it works

Watch a quick simulation of this tool in action — no file needed.

Change Video Speed — in action

Drop a video or click to browse

1. Click the drop zone — pick a video clip to speed up or slow down.

How to use Change Video Speed

Follow these steps — everything happens instantly in your browser.

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Step 1. Drop a video file (under 200 MB recommended).
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Step 2. Pick a playback speed with the slider or the 0.5×–2× presets.
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Step 3. Click “Re-encode at Nx” — the video plays at the chosen rate and is captured in real time.
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Step 4. Download the resulting WebM at the new speed.