mousiki

An Opus decoder library in Rust, ported from the Go implementation in pion/opus. The core crate is #![no_std] and performs zero heap allocations.

Capabilities and limitations (current)

• Mono only; stereo is not supported yet.
• SILK-only mode; Hybrid and CELT are not supported yet.
• Single-frame packets only; multi-frame/variable-frame packets currently return “unsupported”.
• Output is 48 kHz PCM:

  • Either i16 little-endian (LE) or f32, depending on the API you call.

  • A 20 ms frame yields 960 samples (mono), i.e., 1920 bytes for i16 output.

Quick start

Run the examples

• Decode Ogg Opus (mono, SILK-only) to a PCM file:

cargo run --example decode -- testdata/tiny.ogg output_mono.pcm

• Play directly (requires an audio output device; uses cpal):

cargo run --example playback -- testdata/tiny.ogg

Use in your code

The snippet below decodes a single Opus packet into i16 PCM (mono, 48 kHz):

use mousiki::decoder::Decoder;

// `packet` is a single Opus SILK-only, mono packet (already decontainerized; not an Ogg page).
let packet: &[u8] = /* your Opus packet */;

// Output buffer (20 ms -> 960 samples, each sample is 2 bytes for i16)
let mut pcm_bytes = [0u8; 1920];

let mut decoder = Decoder::new();
let (_bandwidth, stereo) = decoder.decode(packet, &mut pcm_bytes)?;
assert!(!stereo, "mono only for now");
// `pcm_bytes` now contains 48 kHz i16 little-endian PCM data

For f32 output, use decode_float32 and a buffer of length 960 for a 20 ms frame:

use mousiki::decoder::Decoder;

let packet: &[u8] = /* your Opus packet */;
let mut pcm_f32 = [0.0f32; 960];

let mut decoder = Decoder::new();
let (_bandwidth, stereo) = decoder.decode_float32(packet, &mut pcm_f32)?;
assert!(!stereo);

Tip: If your input is an Ogg-encapsulated Opus stream, see the example oggreader usage to extract raw Opus packets before decoding.

Compatibility and roadmap

• Target environments: no_std, constrained memory, real-time systems, no dynamic allocation.
• Implemented: SILK-only, mono, single-frame packets, 48 kHz output, basic examples (decode/playback).
• Planned:
  • Stereo support.
  • Hybrid/CELT decode paths.
  • Richer frame structures (multi-frame/variable-frame) support.

License and acknowledgements

• License: MIT (see LICENSE).
• Thanks to the upstream pion/opus (Go) implementation and the community.