Audio Speed Changer Online

Speed up or slow down an audio file, right in the browser.

Key features

• Pick one of eight preset speed factors, from 0.25x (four times slower) up to 4x (four times faster).
• Accepts mp3, wav, aac, ogg, flac, and m4a files, and always downloads a .wav file back - a re-mux that works the same way regardless of which of those formats you started from, so you don't need to check which output codecs your browser's ffmpeg build supports.
• Pitch stays the same - only the tempo changes.

How the speed change works

Changing speed re-encodes the audio (a fresh WAV render via the atempo filter, not a lossless copy), so it takes longer than a simple cut and the output is not byte-identical to the source.

This is a straight tempo change, not a pitch-shifted or reversed effect - a podcast sped up to 1.5x still sounds like the same voice, just talking faster.

When to use it

• Slow a recording to 0.75x or 0.5x when you are transcribing dictation or learning a musical part by ear, and the pitch stays put instead of dropping.
• Reach for the extreme presets - 0.25x for a quarter-speed crawl or 4x for a fast skim - when the everyday 1.25x to 2x range is not enough.
• The 3x and 4x presets stay smooth because the tempo filter is chained in stages for any factor past 2x, rather than stretching in one distorting pass.

Your privacy

The audio is re-rendered inside this browser tab by a self-hosted FFmpeg.wasm engine that runs as a same-origin WebAssembly worker, so the track you load never leaves the page for a server or a third-party service.

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