Speed up or slow down video (0.25×–4×) with pitch-preserving audio. Re-encodes to MP4. 100% in-browser.
Drop a video, pick a speed from 0.25× to 4×, and export with pitch-preserved audio
Video speed changes run entirely in your browser using ffmpeg.wasm. Your video file is never uploaded to any server.
Video timing changes through presentation timestamps: setpts=PTS/2 halves every frame's timestamp, which doubles playback speed. Audio is harder — simply resampling changes pitch (chipmunk effect) — so ffmpeg uses atempo, a phase-vocoder time-stretcher that preserves pitch but only accepts factors between 0.5× and 2×. For 4× speed the tool chains atempo=2.0,atempo=2.0; for 0.25× it chains atempo=0.5,atempo=0.5. Both video and audio are re-encoded (H.264 CRF 20 + AAC) because every timestamp in the file changes.
One atempo covers 0.5×–2×; beyond that factors are chained. 2.5× = 2.0 then 1.25.
Deji recorded a 4:00 (240 s) software walkthrough at a relaxed pace and wants a snappy 1:36 version for his changelog post.
Speed up or slow down video with pitch-preserved audio. In-browser, free.
The Video Speed Controller retimes video anywhere from 0.25× to 4×. Frames are retimed by dividing presentation timestamps (setpts), and audio is stretched or compressed with pitch-preserving chained atempo filters, or dropped entirely. Presets cover the common factors and a fine slider covers everything in between. All processing is local via ffmpeg.wasm.
Drop your video, pick a preset or drag the slider, and check the live output-duration readout. Choose whether to keep the pitch-preserved soundtrack or mute it, then click Apply. The MP4 downloads when the re-encode finishes.
No. The audio passes through ffmpeg's atempo filter, a phase-vocoder time-stretcher that preserves pitch. Because a single atempo only covers 0.5×–2×, larger factors are chained: 2.5× becomes atempo=2.0 followed by atempo=1.25, and 0.25× becomes two chained 0.5 stages.
Output duration equals source duration divided by the speed factor — the tool shows this live as you move the slider (for example, 240 s at 2.5× = 96 s). Both video and audio are re-encoded, so the file is a clean H.264/AAC MP4.
Yes — tick "Remove audio entirely" and the export drops the audio track (-an) while retiming the video. This is common for turning long recordings into quick silent time-lapses.
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