Audio Speed
FFmpeg PoweredAdjust playback speed while preserving pitch
Drag & drop files here, or click to select
Supports MP3, WAV, OGG, M4A, FLAC and other common formatsHow to Use
- Click the area above to select a file, or drag and drop a file onto the page
- Adjust parameters in the settings area
- Click the process button and download the result when ready
Frequently Asked Questions
How It Works
The Audio Speed tool uses FFmpeg WebAssembly with the atempo and asetrate filters to modify audio playback speed. The atempo filter changes speed while preserving pitch using a phase-vocoder algorithm, while asetrate changes the sample rate, affecting both speed and pitch.
The atempo filter works by performing overlap-add (OLA) time-domain processing: the audio is divided into overlapping frames, each frame is analyzed for its spectral content, frames are rearranged at the new time scale, and the overlap regions are cross-faded for smooth output. Each atempo instance supports 0.5x-2.0x, so extreme speeds are achieved by chaining multiple instances.
The pitch-preserving mode uses atempo, while the natural pitch mode uses asetrate (which halves/doubles the sample rate for 2x/0.5x speed). The output is re-encoded to the target format with the adjusted duration. Processing runs on a Web Worker thread for uninterrupted UI interaction.
Tips & Best Practices
- Enable pitch preservation for speech and music — it maintains natural-sounding voice pitch regardless of speed.
- 2x speed is practical maximum for intelligible speech playback. Above 2x, individual words become difficult to distinguish.
- 0.5x speed is ideal for language learning — slows speech enough to hear pronunciation details clearly.
- Combine with trim: Speed up only the slow/padding sections while keeping important content at normal speed.
- Check output duration: 2x speed halves the duration, 0.5x doubles it. Plan accordingly for time-sensitive content.
- For music: Pitch preservation is essential. Without it, 1.5x speed makes music sound like a chipmunk concert.
Use Cases
Language learners slowing down foreign language audio to 0.5x speed to hear pronunciation and catch individual words.
Podcast listeners speeding up episodes to 1.5x or 2x to consume more content in less time during commutes. Music producers creating slow-motion audio effects for transitions and atmospheric sections. Transcription services slowing down fast speakers for more accurate manual transcription. Audio editors creating time-stretched sound effects for film and game audio. Education content creators adjusting narration speed to match visual demonstrations at different pace requirements.