Change Video Speed
Speed a clip up or slow it down, with the audio re-timed instead of pitch-shifted. Runs entirely in your browser.
Re-timing, not resampling
Speeding up video is easy: each frame carries a presentation timestamp saying when to show it, and scaling those timestamps down makes the whole thing play faster. Nothing about the picture changes.
Audio is where tools go wrong. The naive approach is to play the existing samples faster, which is exactly what happens when you spin a record too fast — the pitch rises with the tempo and everybody sounds like a cartoon. The right approach stretches the audio in time while holding the pitch, which is what ffmpeg’s atempo filter does. A double-speed interview still sounds like the same two people, just in a hurry.
The 0.5 to 2.0 limit, and why the range stops at 4x
atempo will not accept a factor outside 0.5 to 2.0 in one instance. Ask it for 4 and the filter graph fails to build, which surfaces to the user as a conversion error that says nothing about audio. The fix is to chain instances — 4x is two doublings — and this page does that automatically, telling you when it happens.
The range stops at 4x because each link in that chain is another pass over the audio, and the quality cost is real. Two links is a sensible ceiling. If you genuinely need more, running the tool twice is both honest about what it is doing and no slower.
When to just drop the sound
At high speeds the audio is often not worth keeping — a timelapse of a build, a long screen recording skimmed at 4x. Turning it off skips the filter chain entirely, which makes the encode faster and avoids stacking resamples on audio nobody will listen to.