opus-rs

A pure-Rust implementation of the Opus audio codec (RFC 6716), ported from the reference C implementation (libopus 1.6).

Status: Production-ready — SILK-only, CELT-only, and Hybrid modes are functional. Stereo encoding (SILK and CELT) is supported.

Features

Pure Rust — no C dependencies, no unsafe code in the codec core
SILK encoder & decoder — narrowband (8 kHz), mediumband (12 kHz), wideband (16 kHz)
CELT encoder & decoder — fullband (48 kHz) with MDCT, PVQ, energy quantization
Hybrid mode — SILK for low frequencies + CELT for high frequencies
Range coder — entropy coding with ICDF tables and Laplace distribution
VAD — voice activity detection
HP filter — variable-cutoff high-pass filter for VOIP mode
CBR / VBR — both constant and variable bitrate modes
LBRR — in-band forward error correction
Resampler — high-quality resampling (up2, up2_hq)
Stereo — mid-side encoding for both SILK and CELT

Quick Start

use opus_rs::{OpusEncoder, OpusDecoder, Application};

// Encode
let mut encoder = OpusEncoder::new(16000, 1, Application::Voip).unwrap();
encoder.bitrate_bps = 16000;
encoder.use_cbr = true;

let input = vec![0.0f32; 320]; // 20ms frame at 16kHz
let mut output = vec![0u8; 256];
let bytes = encoder.encode(&input, 320, &mut output).unwrap();

// Decode
let mut decoder = OpusDecoder::new(16000, 1).unwrap();
let mut pcm = vec![0.0f32; 320];
let samples = decoder.decode(&output[..bytes], 320, &mut pcm).unwrap();

Testing

cargo test

All 156 tests pass, covering MDCT identity, PVQ consistency, SILK/CELT/Hybrid encode/decode roundtrip, resampler tests, and more.

WAV Roundtrip

# Rust encoder/decoder
cargo run --example wav_test

# Compare with C libopus (requires opusic-sys)
cargo run --example wav_test_c

Stereo Tests

cargo run --example stereo_test

Performance

Run all benchmarks:

cargo bench

Run a specific benchmark:

cargo bench -- silk_pitch_analysis_core  # Pitch analysis only
cargo bench -- silk_nsq               # Noise shape quantizer
cargo bench -- silk_burg_modified_fix  # LPC analysis

SILK Encoder (Rust, complexity=0)

Sample Rate	Frame Size	Time per Frame	Throughput
8 kHz	20 ms	13.0 µs	23.5 MiB/s
16 kHz	20 ms	24.3 µs	25.1 MiB/s
16 kHz	10 ms	13.6 µs	22.4 MiB/s

SILK vs C Reference (libopus, complexity=0)

Config	8kHz/20ms	16kHz/20ms	16kHz/10ms
Rust (cx0)	13.3 µs	25.2 µs	13.9 µs
C libopus (cx0)	10.9 µs	18.4 µs	11.3 µs

Both use complexity=0 (fast mode). The C float implementation is ~20-30% faster than Rust's fixed-point implementation. Note: Rust uses fixed-point (Q-domain integer arithmetic) while the C reference uses floating-point.

Full Opus Encoder + Decoder Roundtrip (complexity=0)

Config	Rust	C (opus-sys)	C faster by
8kHz/20ms VoIP	17.7 µs	13.3 µs	33%
16kHz/20ms VoIP	33.3 µs	21.6 µs	55%
16kHz/10ms VoIP	17.3 µs	13.1 µs	32%
48kHz/20ms Audio	172 µs	42.8 µs	4x
48kHz/10ms Audio	99.3 µs	17.7 µs	5.6x

Rust fixed-point encoder + decoder is 1.3-5.6x slower than C floating-point. SILK (VoIP) has smaller gap (~1.3-1.5x), while CELT (Audio) has larger gap (~4-6x).

License

See COPYING for the original Opus license (BSD-3-Clause).

opus-rs 0.1.8