audio-codec

A collection of VoIP audio codecs implemented for Rust. This crate provides a unified interface for encoding and decoding various audio formats commonly used in SIP, VoIP, and WebRTC applications.

Supported Codecs

Codec	Implementation	Feature	no_std
G.711 (PCMA/PCMU)	Pure Rust	Built-in	yes
G.722	Pure Rust	Built-in	yes
G.729	Pure Rust (g729-sys)	Built-in	yes
Opus	Pure Rust (opus-rs)	opus (off by default)	no
Telephone Event	RFC 4733	Built-in	yes
Resampler	Polyphase FIR	Built-in	yes

Features

• Unified API: Simple Encoder and Decoder traits for all codecs.
• no_std support: every codec except Opus runs without std or an allocator.
• Resampler: Built-in audio resampling utility.

Performance

Measured on Apple M2 Pro (processing 20ms audio frames):

Codec	Encode (20ms)	Decode (20ms)	Rate
PCMU	~50.09 ns	~59.73 ns	8kHz
PCMA	~50.23 ns	~59.63 ns	8kHz
G.722	~5.02 µs	~3.82 µs	16kHz
G.729	~20.50 µs	~6.16 µs	8kHz
Opus	~52.34 µs	~23.19 µs	48kHz

Note: Benchmarks were run with cargo bench --bench codec_bench (Criterion). create_encoder(CodecType::Opus) currently uses the default Opus profile: 48kHz, stereo, Application::Audio, bitrate 64kbps, complexity 5.

Usage

Add this to your Cargo.toml:

[dependencies]
audio-codec = { version = "0.4", features = ["opus"] }   # opus is opt-in

Example: Decoding PCMA

use audio_codec::{create_decoder, CodecType};

fn main() {
    let mut decoder = create_decoder(CodecType::PCMA);
    let encoded_data: Vec<u8> = vec![/* ... */];
    let pcm_samples = decoder.decode(&encoded_data);
    
    println!("Decoded {} samples", pcm_samples.len());
}

Example: Encoding G.722

use audio_codec::{create_encoder, CodecType, Encoder};

fn main() {
    let mut encoder = create_encoder(CodecType::G722);
    let pcm_samples: Vec<i16> = vec![0; 320]; // 20ms @ 16kHz mono
    let encoded_data = encoder.encode(&pcm_samples);
    
    println!("Encoded into {} bytes", encoded_data.len());
}

Example: Configuring Opus (Factory API)

use audio_codec::{
    create_opus_decoder, create_opus_encoder, Decoder, Encoder,
    opus::OpusApplication,
};

fn main() {
    // Explicit Opus encoder/decoder creation
    // 48kHz stereo, Audio mode
    let mut encoder = create_opus_encoder(48_000, 2, OpusApplication::Audio);
    let mut decoder = create_opus_decoder(48_000, 2);

    let pcm_samples: Vec<i16> = vec![0; 960 * 2]; // 20ms @ 48kHz, interleaved stereo
    let encoded_data = encoder.encode(&pcm_samples);
    let decoded_pcm = decoder.decode(&encoded_data);

    println!("Encoded into {} bytes", encoded_data.len());
    println!("Decoded {} samples", decoded_pcm.len());
}

no_std support

The crate works on bare-metal targets with no allocator (e.g. Cortex-M, RISC-V). Disable the default std feature and use the slice-based *_into API:

[dependencies.audio-codec]
version = "0.4"
default-features = false

use audio_codec::{Encoder, Decoder, CodecError, g722};

fn g722_roundtrip(
    encoder: &mut g722::G722Encoder,
    decoder: &mut g722::G722Decoder,
    pcm: &[i16],
) -> Result<usize, CodecError> {
    // Caller-provided scratch buffers — no allocation.
    let mut enc_buf = [0u8; 160];           // 20ms @ 16kHz = 160 bytes
    let mut dec_buf = [0i16; 320];

    let n = encoder.encode_into(pcm, &mut enc_buf)?;
    let m = decoder.decode_into(&enc_buf[..n], &mut dec_buf)?;
    Ok(m)
}

Use max_encode_bytes / max_decode_samples to size the buffers correctly:

let needed_bytes = encoder.max_encode_bytes(pcm.len());
let needed_samples = decoder.max_decode_samples(n_bytes);

Resampler in no_std

Resampler borrows a caller-provided coefficient buffer (~24 KB):

use audio_codec::resampler::{Resampler, COEFFS_LEN};

let mut coeffs: [f32; COEFFS_LEN] = [0.0; COEFFS_LEN];
let mut r = Resampler::new(8000, 16000, &mut coeffs)?;

let mut out = [0i16; 160];
let n = r.resample_into(&input[..80], &mut out)?;

Supported codecs in no_std

Codec	Status
G.711 (PCMA/PCMU), G.722, G.729, Telephone Event	✅ fully supported
Resampler	✅ fully supported (borrowed coeffs buffer)
Opus	❌ requires std (opt-in via the opus feature)

The crate is verified to compile on thumbv7em-none-eabi and other bare-metal targets. Float math in the resampler goes through libm when std is off.

License

This project is licensed under the MIT License.