# opus-rs
A pure-Rust implementation of the [Opus audio codec](https://opus-codec.org/) (RFC 6716), ported from the reference C implementation (libopus 1.6).
> **Production-ready**
## Features
- **Pure Rust** — no C dependencies
- **High Performance:** Competitive with C libopus on x64/aarch64
- **`#![no_std]` + no `alloc`:** fully heap-free — runs on bare metal, RTOS, and WebAssembly with **no global allocator**
## Quick Start
```rust
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();
// Encode PCM16 directly (issue #28): skip the f32 round-trip in the
// SILK/VoIP path. Output is byte-for-byte identical to `encode()` called
// with the same audio converted via `sample as f32 / 32768.0`.
let input_i16 = vec![0i16; 320]; // 20ms frame at 16kHz
let bytes = encoder.encode_i16(&input_i16, 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();
```
### WAV Roundtrip
```bash
# Rust encoder/decoder
cargo run --example wav_test
```
## `#![no_std]` + no-`alloc` Support
By default opus-rs runs on `std` with the **`heap` feature**: the large codec state
(`OpusEncoder`/`OpusDecoder` working buffers) is allocated with `Box`, so the public
structs are tiny (~1 KB each) and constructing them uses almost no stack.
For `#![no_std]`, disable the default features. The crate then builds as
`#![no_std]` with **no `alloc`** — fully heap-free, no global allocator required —
and every working buffer is an inline, fixed-size array (sized to the Opus worst
case); growable state uses an internal `FixedVec<T, N>` (a tiny `Vec`-like type over
`[MaybeUninit<T>; N]`). In that configuration the structs are large, so place them
in a `static` (wrap init in your own `Once`-like guard) or a dedicated buffer.
```toml
[dependencies.opus-rs]
version = "0.1"
default-features = false
features = ["libm"]
```
The public API (`OpusEncoder`/`OpusDecoder` with `encode`/`decode` writing into caller-provided buffers) is identical in both configurations.
### Feature flags
| `std` | yes | Enables OS-backed runtime x86 SIMD detection (CPUID). Without it the crate is `#![no_std]`. |
| `heap` | yes | Allocates the large codec state on the heap (`Box`), shrinking `OpusEncoder`/`OpusDecoder` to ~1 KB so they can live on ordinary stacks. Requires `std`. |
| `libm` | no | Required for `#![no_std]` builds — provides float math via a pure-Rust port of musl `libm`. Not needed when `std` is on. |
| `portable-atomic` | no | Uses the [`portable-atomic`](https://crates.io/crates/portable-atomic) crate for the lazily built mode table, so the crate builds on targets without compare-and-swap like `thumbv6m-none-eabi` (Cortex-M0/M0+) or `riscv32imc-unknown-none-elf` (ESP32-C3). There you also need its `critical-section` feature, or `--cfg portable_atomic_unsafe_assume_single_core` on single-core chips. |
> Runtime dependency footprint: `std` build → **0 deps**; `no_std` build → **1 dep** (`libm`, pure Rust).
### Notes for `no_std` users
- **Large structs:** without `heap`, every working buffer is inline, so
`OpusEncoder`/`OpusDecoder` are large (~250 KB / ~175 KB each). Place them in a
`static` (wrap init in your own `Once`-like guard) or a dedicated buffer rather
than on the stack. `OpusDecoder::new` still returns the decoder through the stack,
so use `OpusDecoder::init` to build it directly in that memory:
```rust
static mut DECODER: MaybeUninit<OpusDecoder> = MaybeUninit::uninit();
let decoder = OpusDecoder::init(unsafe { &mut *(&raw mut DECODER) }, 48000, 2)?;
```
Test threads use a 16 MB stack (see `.cargo/config.toml`).
- **x86 SIMD:** without `std`, AVX/AVX2 dispatch falls back to compile-time detection. Build with `RUSTFLAGS="-C target-feature=+avx2"` to enable it. aarch64 NEON is unconditional.
- **Packets are capped** at the RFC 6716 maximum of 1276 bytes (the heap-free range-coder buffer is sized accordingly); standalone `RangeCoder`/CELT use supports up to 2048 bytes.
- **Verified targets:** `thumbv7em-none-eabi` (Cortex-M), `wasm32-unknown-unknown`, and any Linux no_std target. With `portable-atomic`, also `thumbv6m-none-eabi` and `riscv32imc-unknown-none-elf`. Check with `scripts/check_no_std.sh`.
## Performance
Criterion benchmark (`cargo bench --bench opus_vs_c_bench`) with 20 samples, 100 ms warm-up, 500 ms measurement, real speech input (`fixtures/answer_16k.wav`), mono encode-only. All numbers below are wall-clock time for the full frame set.
### vs C Opus (libopus 1.6.1) on x86-64 (AVX2/FMA)
Measured on AMD Ryzen 7 5700X, compiled with `--release` (opt-level=3 + ThinLTO).
| 8 kHz / 20 ms VoIP | **39.9 ms** | 40.6 ms | 0.98× (**Rust 2% faster**) |
| 16 kHz / 20 ms VoIP | **66.8 ms** | 67.1 ms | 1.00× (**Rust 0.5% faster**) |
| 16 kHz / 10 ms VoIP | 73.2 ms | **72.5 ms** | 1.01× (within noise) |
| 48 kHz / 20 ms Audio | **25.1 ms** | 28.4 ms | 0.88× (**Rust 12% faster**) |
| 48 kHz / 10 ms Audio | **29.7 ms** | 31.2 ms | 0.95× (**Rust 5% faster**) |
### vs C Opus (libopus 1.6.1) on Apple Silicon
Measured on Apple Silicon M-series (aarch64), compiled with `--release` (opt-level=3 + ThinLTO), latest run on 2026-04-23.
| 8 kHz / 20 ms VoIP | 31.47 ms | **31.20 ms** | 1.01× (C 0.9% faster) |
| 16 kHz / 20 ms VoIP | **51.19 ms** | 52.81 ms | 0.97× (**Rust 3.1% faster**) |
| 16 kHz / 10 ms VoIP | 55.69 ms | **55.49 ms** | 1.00× (within noise) |
| 48 kHz / 20 ms Audio | **13.97 ms** | 19.39 ms | 0.72× (**Rust 28% faster**) |
| 48 kHz / 10 ms Audio | **16.19 ms** | 20.28 ms | 0.80× (**Rust 20% faster**) |
## Release Notes
### Unreleased
### 0.1.38
- **Fix: a Hybrid frame's mode-switch redundancy now decodes as libopus's
does.** The 5 ms redundant CELT frame (RFC 6716 §4.5.1) used to be read
but never decoded, and the frame's own CELT layer was skipped: every
Hybrid↔CELT switch glitched for 40–60 ms. The main layer now decodes from
the bytes before the redundant frame, the redundant frame decodes with all
bands (from the old CELT state going to SILK, from a reset state going to
CELT) and crossfades in with the CELT window; only a SILK-to-CELT frame's
redundancy sets `prev_redundancy` (PR #58). Worst switch window vs
libopus: 2 dB → 129 dB.
- **Fix: CELT's energy history starts at −28 dB, as libopus's reset sets
it, and the bands a frame doesn't code forget their energies (PR #59).**
Starting at 0 made anti-collapse inject extra noise into the first two
transient frames: CELT's first packets decoded 25–45 dB from libopus.
Now 119 dB at the onset.
- **Fix: a super-wideband Hybrid frame's CELT layer ends at band 19, from
the packet's bandwidth as in libopus (PR #60).** It read two bands its
encoder never coded and sat 10–15 dB from libopus throughout. Now 143 dB.
- **Fix: switches out of CELT reset SILK and bridge with 5 ms of the old
CELT state concealed forward, as libopus does (PR #61).** opus-rs kept the
SILK state (and resampler) from before the CELT run and bridged with the
previous frame's last 5 ms, which had already played: a ~25 ms click at
every CELT→SILK/Hybrid switch. Now 132 dB at the switch.
- **New: `OpusDecoder::init(slot, sampling_rate, channels)` builds the
decoder in place (PR #65, issue #62 item 1).** Without `heap`,
`OpusDecoder::new` returns ~175 KB by value through the stack, which no
MCU has; `init` writes it straight into a `static`. `new` goes through
`init`, so the two cannot drift. `init`'s stack frame is 44 bytes.
- **New: build on targets without compare-and-swap atomics via the
optional `portable-atomic` feature (PR #64, issue #62 item 2).** Enables
`thumbv6m-none-eabi` (Cortex-M0/M0+) and `riscv32imc-unknown-none-elf`
(ESP32-C3); there you also pick how portable-atomic emulates CAS (its
`critical-section` feature, or `--cfg portable_atomic_unsafe_assume_single_core`
on single-core chips). Nothing changes when the feature is off.
- **Fix: SILK CBR with in-band FEC busted packets into concealed frames
(issue #51).** SILK's frame target now leaves room for the packet's LBRR
section, as libopus's does. This ports `enc_API.c`'s per-frame target, for
mono and stereo: the moving average of LBRR bits (`nBitsUsedLBRR`), the
bit reservoir across packets (`nBitsExceeded`) and the balance within a
multi-frame packet (`bitsBalance`). The frame cap no longer takes the
LBRR bits off a second time, since the rate control already counts them.
At 16-48 kb/s, 20 ms and 40% loss, mono busts 0-1 packets in 50 (was up
to 8; libopus 0-2) and stereo 0-2 (was up to 15). Stereo carries LBRR in
22-31 packets (was 5-20; libopus 29-30). Mono's main frame codes as well
as without FEC (worst window 4.6 dB, was 0.3). Hybrid's SILK layer also
pays back its overshoot of the target rate, as libopus's does.
- **Stereo SILK/Hybrid codes the side, as libopus does (issue #48).** L and R
are resampled separately and converted to mid/side at the internal rate by
a bit-exact port of libopus's `silk_stereo_LR_to_MS`: predictor estimation
and quantization, stereo-width smoothing, the panned-mono and reduced-width
decisions, and the mid/side bit split. A second SILK channel codes the
side, with its own VAD, LBRR (in-band FEC) and rate control, and libopus's
side reset after mid-only frames. On the #42 signal each channel now
measures within 0.3 dB of libopus (R: +3.8 → +5.1 dB, libopus +5.1).
Anti-phase input, which decoded as silence, measures +7.0 dB per channel,
as libopus does. Two unrelated voices go from +1.9/+2.8 to +6.0/+9.3 dB
(libopus +5.4/+8.0). Hybrid splits its SILK rate per channel, as libopus's
`compute_silk_rate_for_hybrid` does. Mono output is unchanged, byte for
byte. Under CBR with in-band FEC the side's LBRR at first crowded LBRR
out of many packets; #51 (above) fixes that.
- **Fix: stereo SILK/Hybrid decoded as L ≈ −0.63·mid, R ≈ 2.63·mid (issue
#42).** The encoder codes stereo SILK as the mid only, but wrote stereo
predictor index 0, which dequantizes to `pred_Q13 = (0, −13364)`. The
decoder applies the predictor to mid-only frames too, so the left channel
came out phase-inverted and the right ~8 dB hot. It now writes the zero
predictor, joint symbol 12, as libopus does for its `toMono` frames. Hybrid
also fed SILK the interleaved L,R input as if it were mono; it is now
downmixed like SILK-only, which lifts the 24/48 kHz Hybrid mid from −2.4 dB
to +5.8 dB SNR (libopus +5.9 dB). Both channels now carry the mid
(L = R ≈ 0.85·mid, SNR +5.2/+3.8 dB, libopus +5.1/+5.1 dB with real side
coding), until #48 (above) adds the side.
- **Fix: the SILK decoder's stereo predictor levels match libopus.** The
half-step constant was `(1 << 16) / 10` = 6553 instead of libopus's
`SILK_FIX_CONST(0.1, 16)` = 6554, so 45 of the 75 levels came out a few
Q13 units off and libopus stereo streams decoded at ~65 dB against libopus
instead of bit-exactly. The stereo state is no longer cleared on frames
whose predictor is zero (libopus clears it only on a mono→stereo switch),
and a lost frame keeps the last mid-only flag and conceals the side only
if the last good frame coded one (dec_API.c).
- **Fix: SILK-only VBR ignored `bitrate_bps` (issue #43).** The SILK target
rate came from the packet budget, which under VBR is the caller's output
buffer: a 1500-byte buffer asked SILK for ~510 kb/s, so every bitrate coded
the same ~87-byte packets (16 kHz, 20 ms). The rate now follows libopus
1.6's `bits_target` / `total_bitRate` (opus_encoder.c): the requested
bitrate, capped by the buffer, less the TOC byte. The buffer stays the hard
cap (`maxBits`). At 12-64 kb/s, 16 kHz VBR now codes 21-69 bytes a packet,
against libopus's 27-73. CBR and Hybrid streams are byte-identical to
before. Known gap: at wideband, opus-rs codes fewer excitation bits than
libopus at the same gains (0.78x libopus's size at 12 kb/s, 1.01x at
narrowband). That is a separate SILK encoder divergence, tracked for
follow-up.
- **Fix: mediumband (12 kHz) SILK decoded to noise (issue #53).** The decoder
gave 12 kHz the NB/MB NLSF codebook (order 10) but the wideband LPC order
(16), so it built a 16-tap synthesis filter from ten decoded NLSFs. Every
mediumband packet, from libopus or from opus-rs, decoded to loud noise at
every output rate (-14 to -18 dB against libopus). The order and the
codebook now come from one branch, as in libopus's `decoder_set_fs.c`: mono
mediumband decodes bit-exactly against libopus, and stereo matches it as
far as the stereo predictor allows (issue #42).
- **Fix: a stereo decoder rejected mono packets, and a mono decoder rejected
stereo ones (issue #62, item 3).** `OpusDecoder::decode` returned "Channel
count mismatch between packet and decoder" whenever a packet's ToC
disagreed with the decoder, and libopus stereo encoders send mono packets
at low bitrates. Both now decode as in libopus. A stereo decoder plays a
mono packet on both channels. A mono decoder plays a stereo packet's mid
(SILK) or the average of its channels' spectra (CELT). Channel switches
mid-stream follow `silk/dec_API.c`, which starts the side channel and the
right resampler afresh when a stream turns stereo. SILK decodes bit-exactly
against libopus in every case, switches included. CELT and Hybrid agree
with libopus as closely as when the channel counts match (47-62 dB).
Streams whose channel count matches the decoder's decode exactly as
before. CELT's clearing of the bands a frame doesn't code (#59) now covers
both halves of the energy state, as libopus's does. A mono stream keeps
the second half, and stale energies there made a wider frame decode its
new bands as noise (-0.9 dB against libopus).
### 0.1.37
- **Fix: starved CBR budgets (issues #45, #46).** Budgets below 3 bytes per
frame (and other starved budgets) now emit libopus's TOC-only "PLC" packet
— padded under CBR, with the 40/60 ms multiframe TOC rules — instead of
failing with a range-coder error (debug builds panicked in
`RangeCoder::shrink`). Budgets below ~6 kb/s (9 kb/s above 20 ms) switch to
CELT-only mode and code small valid packets, as libopus does
(opus_encoder.c:1226-1286, 1525-1527). Known gap: at 5-6 byte CELT packets
the payload's tail bits differ from libopus's, costing some SNR — tracked
for follow-up.
- **Fix: 60 ms SILK packets cap the first two frames at 2/5 and 3/4 of the
packet (enc_API.c parity, from PR #44).** Without the caps a 60 ms packet's
early frames could leave the last one under its no-pulse fallback cost.
- **CELT transients are analysed on unfiltered history (PR #47).** The
tone/transient analysis saw a prefiltered overlap head against an
unfiltered body, reading a comb-filter step as a transient on steady
pitched input; 48 kHz Audio at 20-24 kbps lost its first ~200 ms. Now
lag 0, correlation 1.00 from the first window, and only the onset frame
is coded with short blocks.
### Unreleased
- **Fix: CELT from 24 kHz input stuck at ~20 dB SNR (issue #54).** When
`run_prefilter` cancelled the pitch pre-filter for a frame (libopus 1.6's
`cancel_pitch`), it restored the unfiltered input over the whole frame.
libopus still fades the previous frame's comb filter out over the overlap
(celt_encoder.c:1572-1584), and the decoder's post-filter always applies
that fade. So every cancel right after an "on" frame left 120 samples the
decoder post-filtered but the encoder never pre-filtered. From 24 kHz the
zero-stuffed input is dominated by its image above 12 kHz, so the filter
was cancelled whenever the pitch period was odd, in 18 of 66 frames on the
issue's chirp. The SNR was 20.1 / 20.9 / 21.1 dB at 32 / 64 / 128 kbps and
is now 29.4 / 36.2 / 41.9 dB. libopus 1.6.1 scores 38.8 / 41.9 dB at 64 /
128 kbps (35.2 / 41.1 with its tonality analysis off, which opus-rs does
not port). The 48 kHz chirp packets are byte-identical.
- **Fix: CELT flagged transients on steady pitched input (issue #38).** The
encoder ran `tone_detect` and `transient_analysis` on a buffer whose
overlap head was the previous frame's *prefiltered* signal while the body
was unfiltered; libopus 1.6 analyses the unfiltered `prefilter_mem` tail
(celt_encoder.c:2017). Wherever the comb filter was active, the step at the
head read as a transient: on the issue's chirp, 30 of 65 frames were coded
with short blocks at every bitrate (libopus: only the onset frame). With
bits to spare this was inaudible, but 48 kHz `Audio` at 20-24 kbps
(CELT-only) lost its first ~200 ms (correlation 0.56-0.66); it is now lag 0
and correlation 1.00 from the first window, like libopus's CELT.
`prefilter_mem` is also kept current while the comb filter is off (stereo,
hybrid, complexity < 5), as libopus's always-run `run_prefilter` does.
### 0.1.36
- **Fix: in-band FEC emitted no LBRR at CBR (issue #36).** The LBRR payload
reused the main frame's quantized pulses with only the first gain index
raised, so it cost as many bits as the main frame and never fit a CBR
packet. `silk_LBRR_encode` is now ported faithfully: the excitation is
re-quantized through the noise-shaping quantizer at the raised LBRR gain
with its own NSQ state and gain chain, gated on speech activity, with
`silk_setup_LBRR` (gain increase 7, then `max(7 − 0.2·loss, 2)`) and
opus_encoder.c's `decide_fec` (rate thresholds + hysteresis + bandwidth
reduction). CBR mono now recovers the previous packet through libopus
`decode_fec` at 3.8 dB median (previously 0.0 dB: no LBRR at all).
- **Fix: 48 kHz SILK/hybrid encoder delay and startup (issue #38).** The
encoder input was resampled with the stateless `down2`/`down2_3` decimators
plus an internal-rate delay buffer, lagging libopus's pre-skip by up to 17
samples. The encoder now runs the libopus `silk_resampler` (encoder
direction: `delay_matrix_enc` + private down-FIR, ported with the
`silk_Resampler_*_COEFS` tables) on the API-rate input, and prefills the
SILK encoder on CELT→SILK restarts. Measured with the issue's harness:
Voip 32 kbps lag −5..−2 (libopus's own encoder: identical), Audio 24 kbps
startup correlation 0.56 → ≥ 0.77.
- **Fix: panics found by fuzzing.** 2.5 ms CELT frames aborted in the
encoder's lm search (off-by-one: lm=0 was excluded from the valid set);
2.5/5 ms frames reached the SILK encoder, whose VAD band split is only
valid for ≥ 10 ms frames — SILK-only now rejects sub-10 ms frame sizes
(they are CELT-only durations in libopus) and the VAD bails out on
non-multiple-of-8 lengths.
- **no_std:** the crate builds and the full test suite runs with
`--no-default-features --features libm` (`RUST_MIN_STACK=33554432`, see
`scripts/check_no_std.sh`). 13 fuzz targets run clean.
### 0.1.35
- **Fix: SIGILL on AVX-without-FMA CPUs (issue #30, PR #31).** Nine kernels
compiled with `#[target_feature(enable = "avx,fma")]` / `"avx2,fma"` were
dispatched after checking only AVX/AVX2. New `compat::x86_has_avx_fma()` /
`x86_has_avx2_fma()` probes gate them, so Sandy/Ivy Bridge and VMs that mask
FMA no longer fault on the first `vfmadd`.
- **Fix: frame-loss concealment (issue #15, PR #32).** Packets of 0 or 1 bytes
were decoded using the placeholder byte's ToC, which switched the decoder's
mode/bandwidth/SILK rate and could panic in the resampler. Losses now conceal
in the previous mode, as libopus does; an empty packet conceals `frame_size`
samples instead of erroring, and a mono marker no longer errors on a stereo
decoder.
- **Fix: in-band FEC LBRR desync (issue #27, PR #33).** LBRR frames were coded
with `CODE_INDEPENDENTLY_NO_LTP_SCALING` while every decoder reads
`CODE_INDEPENDENTLY`, so a voiced LBRR frame desynced the main frame that
followed it. The LBRR gain bump now raises only index 0 of independently
coded frames, as libopus does.
- **Fix: SILK decoder alignment with libopus (issue #34).** Mono SILK output
read from `w_silk_buf[0][2..]` instead of libopus's `[1..]`, running one
internal-rate sample early, and equal API/SILK-internal rates bypassed
`silk_resampler`, dropping its `inputDelay`. Mono SILK now matches libopus at
lag 0 at 16 kHz and 48 kHz.
- **Fix: 40/60 ms frames (issue #35).** Frame sizes were validated by
`sampling_rate % frame_size == 0`, which rejected 60 ms (16.67 frames/s)
before encoding. Validation is now duration-based. SILK-only carries a
60 ms frame directly (3 internal SILK frames); CELT and Hybrid, which cap a
frame at 20 ms, repacketize 20 ms sub-frames into one code 1/2/3 packet, as
libopus does. This also fixes the code-3 VBR packet parser, which read frame
lengths and frame data interleaved instead of all lengths first (libopus
layout) — a latent bug that only surfaced once the encoder emitted code 3.
- **Fix: 24 kHz CELT decoded to garbage (issue #37).** The CELT encoder always
coded all 21 bands, while the decoder derives its end band from the TOC
(SWB = 19 at 24 kHz); coding one band more than the decoder reads
desynchronised the range coder, turning every 24 kHz CELT packet into noise.
The encoder now takes `end_band` from the Opus bandwidth
(`CELT_SET_END_BAND`). It also zero-stuffs the API-rate input by
`resampling_factor(Fs)` and scales/zeroes the MDCT output for non-48 kHz
rates, as libopus `celt_preemphasis` / `compute_mdcts` do. 24 kHz `Audio`
now matches libopus (per-window correlation ~1.0, was ~0.04).
- **Tests:** new libopus-oracle suites for SILK multi-frame/FEC (#27),
frame-loss concealment (#15), mono alignment (#34), 40/60 ms frames (#35)
and 24 kHz encoding (#37).
### 0.1.34
- **New: `OpusEncoder::encode_i16()` — native PCM16 entry point (issue #28).**
Callers holding PCM16 audio no longer need to convert to f32 before encoding.
In the SILK/VoIP path the integer high-pass biquad (`hp_cutoff_i16`) is fed
directly from the input — no f32 round-trip, no `[i16; 11520]` temporary
conversion buffer. Output is byte-for-byte identical to `encode()` called
with the same audio converted via `sample as f32 / 32768.0` (SILK-only,
Hybrid and CELT-only modes; verified by a parity test matrix across
8/12/16/24/48 kHz, mono/stereo, complexity 0-10, CBR/VBR, in-band FEC).
The float `encode()` API is unchanged.
- **Fix: `no_std` builds (`--no-default-features --features libm`) compile
again.** The `multistream` decode module (added in 0.1.33) uses `Vec`-based
plumbing and is now gated behind the default `std` feature; the core codec
remains heap-free `no_std`.
- **Zero warnings:** `cargo check` and `cargo clippy --all-targets` are clean
for the default and `no_std` feature sets (dead CELT state fields removed,
tests/examples/benches lint-clean).
### 0.1.29
- **Default build is now heap-backed (issue #12).** A new `heap` feature (on by
default, requires `std`) allocates the large codec state with `Box`, shrinking
`OpusEncoder`/`OpusDecoder` from ~250 KB / ~175 KB to ~1 KB each. Constructing,
encoding and decoding now fit on a 768 KiB stack (previously `OpusEncoder::new`
alone needed ~850 KiB in release / ~2 MiB in debug, overflowing small-stack
threads such as Windows' 1 MiB main thread). Disable default features for the
heap-free `#![no_std]` build, which keeps the inline layout.
- **Tests:** add `tests/stack_usage_test.rs` asserting the structs stay <4 KiB
with `heap`, >100 KiB without it, and that a full construct + encode + decode
round-trip fits in a 768 KiB stack thread.
### 0.1.28
- **Fix: high-bitrate bitstream interop with libopus (issue #11).** The ported `BAND_ALLOCATION` table was missing one `200` in its final row (7 entries instead of 8), shifting the whole row. That row is only selected by the allocator at high bitrates, so encoded stereo streams above ~160 kbps decoded to garbage in libopus (and the crate decoder mis-decoded libopus streams at the same rates). Table now byte-identical to libopus.
- **Fix: `celt_pvq_u`/`celt_pvq_v` panic for `k >= 129`.** `compute_u`'s fixed-size buffer is now domain-checked (`k <= MAX_PVQ_K = 128`); out-of-domain calls return `u32::MAX` instead of panicking or silently wrapping.
- **Fix: silent u32 overflow in PVQ codebook sizes.** `compute_u`/`unext`/`celt_pvq_v` use saturating arithmetic, so an out-of-domain `(n, k)` can never produce a plausible-but-wrong codebook size.
- **Fix: `celt_pvq_u_lookup` row-extent aliasing.** Lookups whose `max(n, k)` exceeds a row's actual coverage now compute instead of reading the next row's block.
- **Fix: `OpusEncoder::encode` now returns an error when the range coder overflows its packet budget** (previously bytes were silently dropped).
- **Tests:** add full-domain PVQ table verification vs exact big-int recurrence, out-of-domain saturation checks, and a high-bitrate (128–192 kbps) stereo interop test that cross-checks against libopus.
### 0.1.27
- **`#![no_std]` with no `alloc`**: the crate is now fully heap-free — no global allocator is required. All `Vec`/`Box` working buffers were replaced with an internal `FixedVec<T, N>` (inline `[MaybeUninit<T>; N]`); `std::sync::LazyLock` was replaced with a heap-free `OnceCell`; no_std float math (`sin`/`cos`/`sqrt`/…) is routed through an optional `libm` feature (pure-Rust musl port).
- Verified on `thumbv7em-none-eabi` (Cortex-M), `wasm32-unknown-unknown`, and Linux no_std. `scripts/check_no_std.sh` reproduces.
- Feature flags: `std` (default) → 0 runtime deps; `default-features = false, features = ["libm"]` → 1 dep (`libm`).
- Encoder/decoder structs are inline and large (~250 KB / ~175 KB); place them in a `static` or dedicated buffer on constrained targets.
- **Performance:** unchanged vs 0.1.26 (measured within ±0.5% on `opus_real`; no per-frame allocation overhead).
- **Conformance:** RFC 6716 1276-byte packet cap enforced on the Opus path; the standalone `RangeCoder`/CELT buffer supports up to 2048 bytes.
- `wav_test` example now tags output files by build (`_std` / `_nostd`) for A/B listening across build modes.
## License
See [COPYING](COPYING) for the original Opus license (BSD-3-Clause).
## Links
- **RustPBX**: <https://github.com/restsend/rustpbx>
- **RustRTC**: <https://github.com/restsend/rustrtc>
- **SIP Stack**: <https://github.com/restsend/rsipstack>
- **Rust Voice Agent**: <https://github.com/restsend/active-call>