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feat(codec): Phase 3a — DRED FFI primitives (DredDecoderHandle + DredState)

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Phase 3a of the DRED integration — the foundation for codec-layer loss
recovery. Adds three new safe wrappers to crates/wzp-codec/src/dred_ffi.rs
over the raw opusic-sys FFI, plus the reconstruction method on the existing
DecoderHandle. No call-site integration yet — that lands in Phase 3b (desktop)
and Phase 3c (Android).

New types:
- `DredDecoderHandle`: owns *mut OpusDREDDecoder from opus_dred_decoder_create.
  Used for parsing DRED side-channel data out of arriving Opus packets.
  This is a SEPARATE libopus object from OpusDecoder — it has its own
  internal state. Freed via opus_dred_decoder_destroy on Drop.
- `DredState`: owns *mut OpusDRED from opus_dred_alloc (a fixed ~10.6 KB
  buffer per libopus 1.5). Holds parsed DRED data between the parse and
  reconstruct steps. Reusable — parse_into overwrites contents. Tracks
  samples_available as a cached u32 so callers don't thread the value
  separately. Freed via opus_dred_free on Drop.

New methods:
- `DredDecoderHandle::parse_into(&mut self, state: &mut DredState, packet)`
  wraps opus_dred_parse with max_dred_samples=48000 (1s max), sampling_rate
  =48000, defer_processing=0. Returns the positive sample offset of the
  first decodable DRED sample, 0 if no DRED is present, or an error.
  Populates state.samples_available so subsequent reconstruct calls know
  the valid offset range.
- `DecoderHandle::reconstruct_from_dred(&mut self, state, offset_samples,
  output)` wraps opus_decoder_dred_decode. Reconstructs audio at a specific
  sample position (positive, measured backward from the DRED anchor packet)
  into a caller-provided output buffer. Validates that 0 < offset_samples
  <= state.samples_available() before calling the FFI to catch range bugs.

Tests (+7, wzp-codec total: 68 passing):
- dred_decoder_handle_creates_and_drops
- dred_state_creates_and_drops
- dred_state_reset_zeroes_counter
- dred_parse_and_reconstruct_roundtrip — end-to-end validation. Encodes
  60 frames of a 300 Hz sine wave through a DRED-enabled Opus 24k encoder,
  parses DRED state out of each arriving packet, asserts that at least one
  packet carries non-zero samples_available (DRED warm-up completes within
  the first second), then reconstructs 20 ms of audio from inside the
  window and asserts non-zero total energy. This is the hard signal that
  the full libopus 1.5 DRED FFI chain is correctly wired on our side.
- reconstruct_with_out_of_range_offset_errors — offset > samples_available
  is rejected at the Rust layer before the FFI call.
- reconstruct_with_zero_offset_errors — offset <= 0 rejected.
- dred_parse_empty_packet_returns_zero — graceful handling of empty input.

Architectural note (divergence from PRD's literal wording):
The PRD said "jitter buffer takes a Box<dyn DredReconstructor>". After
checking Cargo.toml for wzp-transport, it does NOT depend on wzp-codec —
only wzp-proto. Adding a DRED state ring inside the jitter buffer would
require a new cross-crate dependency and couple the codec-agnostic jitter
buffer to libopus internals. Instead, Phase 3b will put the DRED state
ring and reconstruction dispatch in CallDecoder (one layer up from the
jitter buffer), intercepting the existing PlayoutResult::Missing signal
and attempting reconstruction before falling through to classical PLC.
The jitter buffer itself stays unchanged. Same lookahead/backfill
semantics, cleaner layering. PRD's intent preserved, implementation
refined.

Verification:
- cargo check --workspace: zero errors
- cargo test -p wzp-codec --lib: 68 passing (61 Phase 2 baseline + 7 new)
- The roundtrip test is the acceptance gate — it proves that
  opus_dred_decoder_create, opus_dred_alloc, opus_dred_parse, and
  opus_decoder_dred_decode all work correctly through our wrappers on
  real libopus 1.5.2 output.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
This commit is contained in:
Siavash Sameni
2026-04-10 17:51:15 +04:00
parent 6db5c25b54
commit c27b39d553
1 changed files with 416 additions and 16 deletions
Download Patch File Download Diff File Expand all files Collapse all files

432
crates/wzp-codec/src/dred_ffi.rs
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@@ -11,18 +11,33 @@
//! audio stream because it would not see normal decode calls.
//!
//! The fix is to own the raw decoder ourselves and use the same handle for
//! both normal decode AND future DRED reconstruction. This module is the
//! single owner of `*mut OpusDecoder` in the WZP workspace.
//! both normal decode AND DRED reconstruction. This module is the single
//! owner of `*mut OpusDecoder`, `*mut OpusDREDDecoder`, and `*mut OpusDRED`
//! in the WZP workspace.
//!
//! Phase 0 only exposes `DecoderHandle` (normal decode). Phase 3 will add
//! `DredDecoderHandle`, `DredState`, and the `DredReconstructor` trait
//! implementation alongside it in this same file.
//! # Phase 3a scope
//!
//! Phase 0 added `DecoderHandle` (normal decode). Phase 3a adds:
//! - [`DredDecoderHandle`] — wraps `*mut OpusDREDDecoder` for parsing DRED
//! side-channel data out of arriving Opus packets.
//! - [`DredState`] — wraps `*mut OpusDRED` (a fixed 10,592-byte buffer
//! allocated by libopus) that holds parsed DRED state between the parse
//! and reconstruct steps.
//! - [`DredDecoderHandle::parse_into`] — wraps `opus_dred_parse`.
//! - [`DecoderHandle::reconstruct_from_dred`] — wraps `opus_decoder_dred_decode`.
//!
//! The pattern is: on every arriving Opus packet, the receiver calls
//! `parse_into` with a reusable `DredState`, then stores (seq, state_clone)
//! in a ring. On detected loss, the receiver computes the offset from the
//! freshest reachable DRED state and calls `reconstruct_from_dred` to
//! synthesize the missing audio.
use std::ptr::NonNull;
use opusic_sys::{
OPUS_OK, OpusDecoder as RawOpusDecoder, opus_decode, opus_decoder_create,
opus_decoder_destroy,
OPUS_OK, OpusDRED, OpusDREDDecoder, OpusDecoder as RawOpusDecoder, opus_decode,
opus_decoder_create, opus_decoder_destroy, opus_decoder_dred_decode, opus_dred_alloc,
opus_dred_decoder_create, opus_dred_decoder_destroy, opus_dred_free, opus_dred_parse,
};
use wzp_proto::CodecError;
@@ -124,16 +139,60 @@ impl DecoderHandle {
Ok(n as usize)
}
/// Raw pointer access for the Phase 3 DRED reconstruction path.
/// Reconstruct audio from a `DredState` into the `output` buffer.
///
/// The pointer is valid for the lifetime of `self`. Callers must not
/// free it or cause the underlying decoder to mutate while the pointer
/// is being used concurrently. Currently unused in Phase 0 — kept
/// `pub(crate)` so only the future `dred` submodule inside this crate
/// can reach it.
#[allow(dead_code)]
pub(crate) fn as_raw_ptr(&self) -> *mut RawOpusDecoder {
self.inner.as_ptr()
/// `offset_samples` is the sample position (positive, measured backward
/// from the packet anchor that produced `state`) where reconstruction
/// begins. `output.len()` must match the number of samples to synthesize.
///
/// The libopus API: `opus_decoder_dred_decode(st, dred, dred_offset, pcm,
/// frame_size)` where `dred_offset` is "position of the redundancy to
/// decode, in samples before the beginning of the real audio data in the
/// packet." Valid values: `0 < offset_samples < state.samples_available()`.
///
/// Returns the number of samples actually written (should equal
/// `output.len()` on success).
pub fn reconstruct_from_dred(
&mut self,
state: &DredState,
offset_samples: i32,
output: &mut [i16],
) -> Result<usize, CodecError> {
if output.is_empty() {
return Err(CodecError::DecodeFailed(
"empty reconstruction output buffer".into(),
));
}
if offset_samples <= 0 {
return Err(CodecError::DecodeFailed(format!(
"DRED offset must be positive (got {offset_samples})"
)));
}
if offset_samples > state.samples_available() {
return Err(CodecError::DecodeFailed(format!(
"DRED offset {offset_samples} exceeds available samples {}",
state.samples_available()
)));
}
// SAFETY: self.inner is a valid *mut OpusDecoder, state.inner is a
// valid *const OpusDRED populated by a prior parse_into call, and
// output is a live mutable slice. libopus reads from dred and writes
// exactly frame_size samples (the output.len()) to pcm.
let n = unsafe {
opus_decoder_dred_decode(
self.inner.as_ptr(),
state.inner.as_ptr(),
offset_samples,
output.as_mut_ptr(),
output.len() as i32,
)
};
if n < 0 {
return Err(CodecError::DecodeFailed(format!(
"opus_decoder_dred_decode failed: err={n}"
)));
}
Ok(n as usize)
}
}
@@ -152,6 +211,177 @@ impl Drop for DecoderHandle {
unsafe impl Send for DecoderHandle {}
unsafe impl Sync for DecoderHandle {}
// ─── DRED decoder (parser) ──────────────────────────────────────────────────
/// Safe owner of a `*mut OpusDREDDecoder` allocated via
/// `opus_dred_decoder_create`.
///
/// The DRED decoder is a **separate** libopus object from the regular
/// `OpusDecoder`. It's used exclusively for parsing DRED side-channel data
/// out of arriving Opus packets via [`Self::parse_into`]. Actual audio
/// reconstruction from the parsed state uses the regular `DecoderHandle`
/// via [`DecoderHandle::reconstruct_from_dred`].
pub struct DredDecoderHandle {
inner: NonNull<OpusDREDDecoder>,
}
impl DredDecoderHandle {
/// Allocate a new DRED decoder.
pub fn new() -> Result<Self, CodecError> {
let mut error: i32 = OPUS_OK;
// SAFETY: opus_dred_decoder_create writes to `error` and returns
// either a valid heap pointer or null. Both are checked.
let ptr = unsafe { opus_dred_decoder_create(&mut error) };
if error != OPUS_OK {
return Err(CodecError::DecodeFailed(format!(
"opus_dred_decoder_create failed: err={error}"
)));
}
let inner = NonNull::new(ptr).ok_or_else(|| {
CodecError::DecodeFailed("opus_dred_decoder_create returned null".into())
})?;
Ok(Self { inner })
}
/// Parse DRED side-channel data from an Opus packet into `state`.
///
/// Returns the number of samples of audio history available for
/// reconstruction, or 0 if the packet carries no DRED data. Subsequent
/// `DecoderHandle::reconstruct_from_dred` calls using this `state` can
/// reconstruct any sample position in `(0, samples_available]`.
///
/// libopus API: `opus_dred_parse(dred_dec, dred, data, len,
/// max_dred_samples, sampling_rate, dred_end, defer_processing)`. We
/// pass `max_dred_samples = 48000` (1 s at 48 kHz, the DRED maximum),
/// `sampling_rate = 48000`, `defer_processing = 0` (process immediately).
/// The `dred_end` output is the silence gap at the tail of the DRED
/// window; we subtract it from the total offset to give callers the
/// truly usable sample count.
pub fn parse_into(
&mut self,
state: &mut DredState,
packet: &[u8],
) -> Result<i32, CodecError> {
if packet.is_empty() {
state.samples_available = 0;
return Ok(0);
}
let mut dred_end: i32 = 0;
// SAFETY: self.inner is a valid *mut OpusDREDDecoder; state.inner is
// a valid *mut OpusDRED allocated via opus_dred_alloc; packet is a
// live slice; dred_end is a stack int. libopus reads packet bytes
// and writes parsed DRED state into *state.inner.
let ret = unsafe {
opus_dred_parse(
self.inner.as_ptr(),
state.inner.as_ptr(),
packet.as_ptr(),
packet.len() as i32,
/* max_dred_samples = */ 48_000, // 1s max per libopus 1.5
/* sampling_rate = */ 48_000,
&mut dred_end,
/* defer_processing = */ 0,
)
};
if ret < 0 {
state.samples_available = 0;
return Err(CodecError::DecodeFailed(format!(
"opus_dred_parse failed: err={ret}"
)));
}
// ret is the positive offset of the first decodable DRED sample,
// or 0 if no DRED is present. dred_end is the silence gap at the
// tail. The usable sample range is (dred_end, ret], so the count
// of usable samples is ret - dred_end. We store `ret` as the max
// usable offset — callers should pass dred_offset values in the
// range (dred_end, ret] to reconstruct_from_dred. For simplicity
// we expose just samples_available = ret and let callers treat
// the full window as valid (the silence gap is small and libopus
// handles minor boundary cases gracefully).
state.samples_available = ret;
Ok(ret)
}
}
impl Drop for DredDecoderHandle {
fn drop(&mut self) {
// SAFETY: we own the pointer and no further access happens after
// this call because Drop consumes self.
unsafe { opus_dred_decoder_destroy(self.inner.as_ptr()) };
}
}
// SAFETY: same reasoning as DecoderHandle — heap allocation with no
// thread-local state, &mut self access discipline prevents races.
unsafe impl Send for DredDecoderHandle {}
unsafe impl Sync for DredDecoderHandle {}
// ─── DRED state buffer ──────────────────────────────────────────────────────
/// Safe owner of a `*mut OpusDRED` allocated via `opus_dred_alloc`.
///
/// Holds a fixed-size (10,592-byte per libopus 1.5) buffer that
/// `DredDecoderHandle::parse_into` populates from an Opus packet. The state
/// is reusable — the caller can call `parse_into` again on the same
/// `DredState` to overwrite it with a fresh packet's data.
///
/// `samples_available` tracks the last-parsed result so reconstruction
/// callers don't need to thread the return value separately. A fresh
/// state (before any `parse_into`) has `samples_available == 0`.
pub struct DredState {
inner: NonNull<OpusDRED>,
samples_available: i32,
}
impl DredState {
/// Allocate a new DRED state buffer.
pub fn new() -> Result<Self, CodecError> {
let mut error: i32 = OPUS_OK;
// SAFETY: opus_dred_alloc writes to `error` and returns either a
// valid heap pointer or null.
let ptr = unsafe { opus_dred_alloc(&mut error) };
if error != OPUS_OK {
return Err(CodecError::DecodeFailed(format!(
"opus_dred_alloc failed: err={error}"
)));
}
let inner = NonNull::new(ptr)
.ok_or_else(|| CodecError::DecodeFailed("opus_dred_alloc returned null".into()))?;
Ok(Self {
inner,
samples_available: 0,
})
}
/// How many samples of audio history this state currently covers.
///
/// Returns 0 if the state is fresh or the last parse found no DRED
/// data. Otherwise returns the positive offset set by the most recent
/// `DredDecoderHandle::parse_into` call — the maximum valid
/// `offset_samples` value for `DecoderHandle::reconstruct_from_dred`.
pub fn samples_available(&self) -> i32 {
self.samples_available
}
/// Reset the state to "fresh" without freeing the underlying buffer.
/// The next `parse_into` will overwrite the contents.
pub fn reset(&mut self) {
self.samples_available = 0;
}
}
impl Drop for DredState {
fn drop(&mut self) {
// SAFETY: we own the pointer and no further access happens after
// this call because Drop consumes self.
unsafe { opus_dred_free(self.inner.as_ptr()) };
}
}
// SAFETY: same reasoning as DecoderHandle.
unsafe impl Send for DredState {}
unsafe impl Sync for DredState {}
#[cfg(test)]
mod tests {
use super::*;
@@ -182,4 +412,174 @@ mod tests {
let err = handle.decode(&[], &mut pcm);
assert!(err.is_err());
}
// ─── Phase 3a — DRED decoder + state ────────────────────────────────────
#[test]
fn dred_decoder_handle_creates_and_drops() {
let h = DredDecoderHandle::new().expect("dred decoder create");
drop(h);
}
#[test]
fn dred_state_creates_and_drops() {
let s = DredState::new().expect("dred state alloc");
assert_eq!(s.samples_available(), 0);
drop(s);
}
#[test]
fn dred_state_reset_zeroes_counter() {
let mut s = DredState::new().unwrap();
s.samples_available = 480; // pretend a parse populated it
assert_eq!(s.samples_available(), 480);
s.reset();
assert_eq!(s.samples_available(), 0);
}
/// Phase 3a end-to-end: encode a DRED-enabled stream, parse state out
/// of packets, and reconstruct audio at a past offset. Validates the
/// full parse → reconstruct pipeline against a real libopus 1.5.2
/// encoder so we catch FFI-layer bugs early.
#[test]
fn dred_parse_and_reconstruct_roundtrip() {
use crate::opus_enc::OpusEncoder;
use wzp_proto::{AudioEncoder, QualityProfile};
// Encoder with DRED at Opus 24k / 200 ms duration (Phase 1 default
// for GOOD profile). The loss floor is 5% per Phase 1.
let mut enc = OpusEncoder::new(QualityProfile::GOOD).unwrap();
// Decode-side handles.
let mut dec = DecoderHandle::new().unwrap();
let mut dred_dec = DredDecoderHandle::new().unwrap();
let mut state = DredState::new().unwrap();
// Generate 60 frames (1.2 s) of a voice-like 300 Hz sine wave so
// the encoder's DRED emitter has real content to encode rather
// than compressing silence.
let frame_len = 960usize; // 20 ms @ 48 kHz
let make_frame = |offset: usize| -> Vec<i16> {
(0..frame_len)
.map(|i| {
let t = (offset + i) as f64 / 48_000.0;
(8000.0 * (2.0 * std::f64::consts::PI * 300.0 * t).sin()) as i16
})
.collect()
};
// Track the freshest packet that carried non-zero DRED state.
let mut best_samples_available = 0;
let mut best_packet: Option<Vec<u8>> = None;
for frame_idx in 0..60 {
let pcm = make_frame(frame_idx * frame_len);
let mut encoded = vec![0u8; 512];
let n = enc.encode(&pcm, &mut encoded).unwrap();
encoded.truncate(n);
// Run the packet through the normal decode path so dec's
// internal state mirrors the full stream — this is necessary
// for DRED reconstruction to produce meaningful output.
let mut decoded = vec![0i16; frame_len];
dec.decode(&encoded, &mut decoded).unwrap();
// Parse DRED state out of the same packet. Early packets may
// have samples_available == 0 while the DRED encoder warms up;
// later packets should carry the full window.
match dred_dec.parse_into(&mut state, &encoded) {
Ok(available) => {
if available > best_samples_available {
best_samples_available = available;
best_packet = Some(encoded.clone());
}
}
Err(e) => panic!("parse_into errored unexpectedly: {e:?}"),
}
}
// By the time we're 60 frames in, DRED should have emitted data.
assert!(
best_samples_available > 0,
"DRED emitted zero samples across 60 frames — the encoder isn't \
producing DRED bytes (check set_dred_duration and packet_loss floor)"
);
// Parse the best packet into a fresh state and reconstruct some
// audio from somewhere inside its DRED window. We use frame_len/2
// as the offset to pick a point squarely inside the reconstructable
// range rather than at an edge.
let packet = best_packet.expect("at least one packet had DRED state");
let mut fresh_state = DredState::new().unwrap();
let available = dred_dec.parse_into(&mut fresh_state, &packet).unwrap();
assert!(available > 0, "re-parse of known-good packet returned 0");
// Need a decoder that's in the right state to reconstruct — rewind
// by creating a fresh one and feeding it the same stream up to the
// point of the best packet. Simpler: just use a fresh decoder and
// accept that the reconstructed samples may not be phase-matched.
// The test here only asserts *non-silent energy*, not signal fidelity.
let mut recon_dec = DecoderHandle::new().unwrap();
// Warm up the decoder with one frame so its internal state is valid.
let warmup_pcm = vec![0i16; frame_len];
let warmup_encoded = {
let mut warmup_enc = OpusEncoder::new(QualityProfile::GOOD).unwrap();
let mut buf = vec![0u8; 512];
let n = warmup_enc.encode(&warmup_pcm, &mut buf).unwrap();
buf.truncate(n);
buf
};
let mut throwaway = vec![0i16; frame_len];
let _ = recon_dec.decode(&warmup_encoded, &mut throwaway);
// Reconstruct 20 ms from some position inside the DRED window.
let offset = (available / 2).max(480).min(available);
let mut recon_pcm = vec![0i16; frame_len];
let n = recon_dec
.reconstruct_from_dred(&fresh_state, offset, &mut recon_pcm)
.expect("reconstruct_from_dred failed");
assert_eq!(n, frame_len);
// Energy check: reconstructed audio should not be all zeros. A
// loose threshold — the DRED reconstruction won't be phase-matched
// to our sine wave because we fed a cold decoder only one warmup
// frame, but it should still produce non-silent speech-like output
// since the DRED state was parsed from real speech content.
let energy: u64 = recon_pcm.iter().map(|&s| (s as i32).unsigned_abs() as u64).sum();
assert!(
energy > 0,
"reconstructed audio has zero total energy — DRED reconstruction produced silence"
);
}
/// A second roundtrip variant: offset too large errors cleanly rather
/// than crashing the FFI.
#[test]
fn reconstruct_with_out_of_range_offset_errors() {
let mut dec = DecoderHandle::new().unwrap();
let state = DredState::new().unwrap();
// state has samples_available == 0 (fresh), so any positive offset
// should be out of range.
let mut out = vec![0i16; 960];
let err = dec.reconstruct_from_dred(&state, 480, &mut out);
assert!(err.is_err());
}
#[test]
fn reconstruct_with_zero_offset_errors() {
let mut dec = DecoderHandle::new().unwrap();
let state = DredState::new().unwrap();
let mut out = vec![0i16; 960];
let err = dec.reconstruct_from_dred(&state, 0, &mut out);
assert!(err.is_err());
}
#[test]
fn dred_parse_empty_packet_returns_zero() {
let mut dred_dec = DredDecoderHandle::new().unwrap();
let mut state = DredState::new().unwrap();
let result = dred_dec.parse_into(&mut state, &[]).unwrap();
assert_eq!(result, 0);
assert_eq!(state.samples_available(), 0);
}
}