Speed a video up to 4× or slow it down to half — entirely in your browser, with the audio resampled to match. No upload, no account, no watermark.
When you change a video's speed without doing anything special to the audio, the pitch of every voice and every sound shifts the same way the timing does. Speed it up to 2× and a person's voice rises about an octave — the classic "chipmunk" effect. Slow it down to 0.5× and the voice drops an octave, sounding underwater.
Zimblu does this honestly rather than hiding it. The audio is resampled to match the new playback speed exactly, so it stays in perfect sync with the picture, but the pitch shifts as a natural consequence. Most of the time this is what you actually want: a tutorial sped up to 2× is more watchable, not less, with the voice slightly higher. A slo-mo replay sounds dramatic with the audio bass-y.
Pitch-corrected speed change — where a voice stays at its original pitch while the timing changes — needs a heavier algorithm called phase vocoding. It works well but takes much longer than the rest of the export, and gets harder to do well at speeds above ~1.5×. We've chosen to ship the fast honest version here, and to keep pitch correction as a Zimblu iOS app feature.
Six presets: 0.5× (half speed, twice as long), 1× (no change), 1.5×, 2×, 3× and 4×. We picked these because they cover the vast majority of real needs — slo-mo, speed-up for tutorials, hyperlapse — without burying you in choices.
Yes — that's the honest behaviour of changing speed without pitch correction. Faster makes voices higher, slower makes them deeper. We chose to ship this as the default because pitch-corrected stretching needs heavier processing that takes much longer than the rest of the export, and most people changing speed for a tutorial or a hyperlapse don't care about the audio anyway. Pitch-corrected speed change is on the roadmap for the Zimblu iOS app.
Yes, but only once. To play the same frames at a different speed, the file's per-frame timestamps have to change, which means re-writing the video stream. Zimblu does this in a single decode-and-re-encode pass at a bitrate matched to your source. In our tests, 2×-speeding a 30-second 1080p clip takes about 4 seconds — roughly seven times faster than the original video's length.
Zimblu resamples the audio entirely on your device using the browser's Web Audio engine, then re-encodes the result as AAC alongside the new video. The result is in perfect sync with the picture; only the pitch shifts as a side effect of the speed change.
No. The whole speed change runs inside your browser, on your machine. Your video does not reach a server at any point. You can disconnect from the internet after the page loads and the tool keeps working.