How to stretch audio duration without changing pitch — free
- Step 1Upload your audio file — Drop your audio file.
- Step 2Set stretch factor (e.g. 0.75× for 75% speed) — Enter the stretch factor (0.5 = half speed, 2.0 = double speed).
- Step 3Download the time-stretched audio — Download the time-stretched audio.
Frequently asked questions
What is the difference between time stretching and pitch shifting?+
Time stretching changes duration while preserving pitch — making audio longer or shorter without going up or down in key. Pitch shifting changes pitch while preserving duration. Speeding up by resampling (like playing a tape faster) changes both simultaneously. Time stretch algorithms separate these two properties.
Can I make a 90-minute recording fit into 60 minutes?+
Yes — set the stretch factor to 0.667× (66.7% of original duration). At 1.5× speed, speech remains intelligible for most audio with clear diction. Highly compressed bitrates (under 64 kbps) or recordings with heavy reverb may sound unnatural at 1.5× speed.
What range of stretch factors are supported?+
The atempo filter supports 0.5× to 2× per pass. For more extreme stretches, the filter is chained: 4× slow-down is applied as two passes of 0.5×. Extreme time stretches (below 0.25× or above 4×) produce 'granular synthesis' type artefacts that are creative but not transparent.
Privacy first
All audio processing runs locally in your browser using FFmpeg compiled to WebAssembly. No file is ever uploaded — only metadata counters are saved for signed-in dashboard stats.