Audio speed changer — free online tool

What to know

The speed changer takes MP3, WAV, M4A, AAC, FLAC, OGG, Opus and WebM audio and re-times it with a multiplier from 0.25 to 4 in 0.05 steps. Nine presets sit under the slider: 0.25, 0.5, 0.75, 1, 1.25, 1.5, 2, 3 and 4.

Pitch is preserved. The tool uses ffmpeg's atempo filter, which stretches or squeezes time without shifting the notes, so a voice at 1.5 speed stays at the same pitch. A single atempo stage works between 0.5 and 2, so values outside that range are built from chained stages: 4 becomes atempo=2 twice, and 0.25 becomes atempo=0.5 twice.

The new length is the original divided by the multiplier. A 40-minute lecture at 1.5 becomes 26 minutes 40 seconds, and a 2-minute clip at 0.5 becomes 4 minutes. The preview shows the expected length, so you can confirm it fits before processing.

Two pages open this tool on a preset direction. Speed up starts at 1.25 for lectures and voice notes, and Slow down starts at 0.8 for transcription and practice. The slider and presets are identical on both.

Extreme settings add artifacts. Speech is comfortable up to about 2x, music with strong transients smears sooner, and 4x is for skimming rather than listening.