Crate timestretch 

Pure Rust audio time stretching library optimized for electronic dance music.

timestretch changes the tempo of audio without altering its pitch, using a hybrid algorithm that combines WSOLA (for transients) with a phase vocoder (for tonal content). It ships with five EDM-tuned presets and a streaming API for real-time use.

Quick Start

use timestretch::{StretchParams, EdmPreset};

// 1 second of 440 Hz sine at 44.1 kHz
let input: Vec<f32> = (0..44100)
    .map(|i| (2.0 * std::f32::consts::PI * 440.0 * i as f32 / 44100.0).sin())
    .collect();

let params = StretchParams::new(1.5)
    .with_sample_rate(44100)
    .with_channels(1)
    .with_preset(EdmPreset::HouseLoop);

let output = timestretch::stretch(&input, &params).unwrap();
assert!(output.len() > input.len()); // ~1.5x longer

Streaming

For real-time use, feed audio in chunks via StreamProcessor:

use timestretch::{EdmPreset, StreamProcessor, StretchParams};

let params = StretchParams::new(1.0)
    .with_preset(EdmPreset::DjBeatmatch)
    .with_sample_rate(44_100)
    .with_channels(2);

let mut processor = StreamProcessor::new(params);

let input_chunk = vec![0.0f32; 256 * 2];
let mut output_chunk = Vec::with_capacity(1_024);
processor.process_into(&input_chunk, &mut output_chunk).unwrap();
processor.set_stretch_ratio(1.05).unwrap();
let mut remaining = Vec::with_capacity(1_024);
processor.flush_into(&mut remaining).unwrap();

Re-exports

pub use analysis::beat::BeatGrid;

pub use analysis::preanalysis::analyze_for_dj;

pub use core::preanalysis::read_preanalysis_json;

pub use core::preanalysis::write_preanalysis_json;

pub use core::preanalysis::PreAnalysisArtifact;

pub use core::types::AudioBuffer;

pub use core::types::Channels;

pub use core::types::CrossfadeMode;

pub use core::types::EdmPreset;

pub use core::types::EnvelopePreset;

pub use core::types::FrameIter;

pub use core::types::QualityMode;

pub use core::types::Sample;

pub use core::types::StretchParams;

pub use core::types::TransientThresholdPolicy;

pub use core::window::WindowType;

pub use error::StretchError;

pub use stream::StreamProcessor;

pub use stream::TransientResetStats;

pub use stretch::phase_locking::PhaseLockingMode;

pub use stretch::stereo::StereoMode;

Modules

analysis

Audio analysis: transient detection, beat tracking, frequency analysis, and HPSS.

core

Core types, window functions, and resampling utilities.

error

Error types for the timestretch crate.

io

Audio file I/O (WAV format).

stream

Streaming (chunked) audio processing for real-time use.

stretch

Time stretching algorithms: phase vocoder, WSOLA, and the hybrid combiner.

Functions

bpm_ratio

Returns the stretch ratio needed to change from one BPM to another.

detect_beat_grid

Detects beats and returns a BeatGrid with BPM and beat positions.

detect_beat_grid_buffer

Detects beats in an AudioBuffer and returns a BeatGrid.

detect_bpm

Detects the BPM of a mono audio signal.

detect_bpm_buffer

Detects the BPM of an AudioBuffer.

pitch_shift

Shifts the pitch of audio without changing its duration.

pitch_shift_buffer

Shifts the pitch of an AudioBuffer without changing its duration.

pitch_shift_wav_file

Reads a WAV file, pitch-shifts it, and writes the result to another WAV file.

stretch

Stretches audio samples by the given parameters.

stretch_bpm_buffer

Stretches an AudioBuffer from one BPM to another.

stretch_bpm_buffer_auto

Stretches an AudioBuffer to a target BPM, auto-detecting the source BPM.

stretch_buffer

Stretches an AudioBuffer and returns a new AudioBuffer.

stretch_into

Stretches audio samples, appending the result to a caller-provided buffer.

stretch_to_bpm

Stretches audio from one BPM to another.

stretch_to_bpm_auto

Stretches audio to a target BPM, auto-detecting the source BPM.

stretch_to_bpm_auto_wav_file

Reads a WAV file, auto-detects its BPM, stretches to the target BPM, and writes the result.

stretch_to_bpm_wav_file

Reads a WAV file, stretches it from one BPM to another, and writes the result.

stretch_wav_file

Reads a WAV file, stretches it, and writes the result to another WAV file.