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feat(codec): Phase 1 — enable DRED on all Opus profiles, disable inband FEC

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Phase 1 of the DRED integration (docs/PRD-dred-integration.md). The Opus
encoder now emits DRED (Deep REDundancy) bytes in every packet, carrying
a neural-coded history of recent audio that the decoder can use to
reconstruct loss bursts up to the configured window. Opus inband FEC
(LBRR) is disabled because DRED does the same job better and running both
wastes bitrate on overlapping protection.

Tiered DRED duration policy per PRD:
  Studio  (Opus 32k/48k/64k): 10 frames = 100 ms
  Normal  (Opus 16k/24k):     20 frames = 200 ms
  Degraded (Opus 6k):         50 frames = 500 ms

Each profile switch (via adaptive quality) updates the DRED duration to
match the new tier. A 5% packet_loss floor is applied whenever DRED is
active, because libopus 1.5 gates DRED emission on non-zero packet_loss.
Real loss measurements from the quality adapter override upward.

Escape hatch: AUDIO_USE_LEGACY_FEC=1 reverts the encoder to Phase 0
behavior (inband FEC Mode1, DRED off, no loss floor). Read once at
OpusEncoder::new; call-scoped, not re-read mid-call. Trait-level
set_inband_fec becomes a no-op in DRED mode to preserve the invariant
even if external callers forget.

Observations from the bitrate probe test (dred_mode_roundtrip_voice_pattern):
  DRED mode:   3649 bytes/sec (~29.2 kbps) on Opus 24k + 300 Hz sine
  Legacy mode: 2383 bytes/sec (~19.1 kbps)
  Delta:       +10.1 kbps

The delta is considerably larger than the "+1 kbps flat" figure I carried
into the PRD from hazy memory of published DRED benchmarks. Likely because
the input (300 Hz sine) is very compressible so the base Opus rate in
legacy mode is well below the 24 kbps target, making the delta look
disproportionate. Signal-dependent — real speech would probably show a
different ratio. If production telemetry shows the overhead is excessive,
we can cut DRED duration on the normal tier from 200 ms to 100 ms as a
first tuning lever. Not blocking Phase 1 since the test still passes
within the reasonable 2000–8000 bytes/sec bounds.

Test changes (+8 tests, total wzp-codec: 61 passing):
- dred_duration_for_studio_tiers_is_100ms  (per-profile policy)
- dred_duration_for_normal_tiers_is_200ms
- dred_duration_for_degraded_tier_is_500ms
- dred_duration_for_codec2_is_zero
- default_mode_is_dred_not_legacy  (sanity check on fresh construction)
- dred_mode_roundtrip_voice_pattern  (observes DRED bitrate, asserts bounds)
- profile_switch_refreshes_dred_duration  (verifies set_profile updates DRED)
- set_inband_fec_noop_in_dred_mode  (trait-level inband FEC no-op)

Verification:
- cargo check --workspace: zero errors, no new warnings
- cargo test -p wzp-codec: 61/61 passing (53 pre-Phase-1 baseline + 8 new)
- Empirical DRED bitrate observed via `rtk proxy cargo test
  dred_mode_roundtrip_voice_pattern -- --nocapture`

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
This commit is contained in:
Siavash Sameni
2026-04-10 17:26:34 +04:00
parent 86526a7ad4
commit 54cbebd34e
1 changed files with 305 additions and 28 deletions
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333
crates/wzp-codec/src/opus_enc.rs
View File

@@ -1,25 +1,87 @@
//! Opus encoder wrapping the `opusic-c` crate (libopus 1.5.2).
//!
//! Phase 0 of the DRED integration: swapped FFI backend from audiopus
//! (dead, libopus 1.3) to opusic-c (live, libopus 1.5.2). Behavior is
//! intentionally unchanged from the audiopus-based encoder — inband FEC
//! stays ON, DRED stays at duration 0. Phase 1 enables DRED and disables
//! inband FEC. See docs/PRD-dred-integration.md.
//! Phase 1 of the DRED integration: encoder-side DRED is enabled on every
//! Opus profile with a tiered duration (studio 100 ms / normal 200 ms /
//! degraded 500 ms), and Opus inband FEC (LBRR) is disabled because DRED
//! is the stronger mechanism for the same failure mode. The legacy behavior
//! is preserved behind the `AUDIO_USE_LEGACY_FEC` environment variable as a
//! runtime escape hatch for rollout. See `docs/PRD-dred-integration.md`.
//!
//! # DRED duration policy
//!
//! Rationale from the PRD:
//! - Studio tiers (Opus 32k/48k/64k): 100 ms — loss is rare on high-quality
//! networks; short window keeps decoder CPU modest.
//! - Normal tiers (Opus 16k/24k): 200 ms — balanced baseline covering common
//! VoIP loss patterns (20–150 ms bursts from wifi roam, transient congestion).
//! - Degraded tier (Opus 6k): 500 ms — users on 6k are by definition on a
//! bad link; longer DRED buys maximum burst resilience where it matters.
//!
//! # Why the 5% packet loss floor
//!
//! libopus 1.5's DRED emitter is gated on a non-zero `OPUS_SET_PACKET_LOSS_PERC`.
//! If the encoder thinks loss is 0, it skips DRED encoding even when the
//! duration is set. We force a 5% minimum so DRED emits continuously; real
//! measurements from the quality adapter override upward when loss exceeds
//! the floor.
use opusic_c::{
Application, Bitrate, Channels, Encoder, InbandFec, SampleRate, Signal,
};
use tracing::debug;
use opusic_c::{Application, Bitrate, Channels, Encoder, InbandFec, SampleRate, Signal};
use tracing::{debug, warn};
use wzp_proto::{AudioEncoder, CodecError, CodecId, QualityProfile};
/// Minimum `OPUS_SET_PACKET_LOSS_PERC` value used in DRED mode. libopus gates
/// DRED emission on a non-zero loss hint, so we keep it clamped to at least
/// this floor whenever DRED is active.
const DRED_LOSS_FLOOR_PCT: u8 = 5;
/// Environment variable that reverts Phase 1 behavior to Phase 0 (inband FEC
/// on, DRED off, no loss floor). Read once per encoder construction.
const LEGACY_FEC_ENV: &str = "AUDIO_USE_LEGACY_FEC";
/// Returns the DRED duration in 10 ms frame units for a given Opus codec.
///
/// Unit: each frame is 10 ms, so the max value of 104 corresponds to 1040 ms
/// of reconstructable history. Returns 0 for non-Opus codecs (DRED is not
/// emitted by the libopus encoder in that case anyway, but we avoid a
/// pointless FFI call).
///
/// See the DRED duration policy in the module docs for per-tier rationale.
pub fn dred_duration_for(codec: CodecId) -> u8 {
match codec {
// Studio tiers — loss is rare, short window.
CodecId::Opus32k | CodecId::Opus48k | CodecId::Opus64k => 10,
// Normal tiers — balanced baseline.
CodecId::Opus16k | CodecId::Opus24k => 20,
// Degraded tier — maximum burst resilience.
CodecId::Opus6k => 50,
// Non-Opus (Codec2 / CN): DRED is N/A.
CodecId::Codec2_1200 | CodecId::Codec2_3200 | CodecId::ComfortNoise => 0,
}
}
/// Returns whether the legacy-FEC escape hatch is active.
///
/// Read from `AUDIO_USE_LEGACY_FEC`. Any non-empty value activates legacy
/// mode; unset or empty leaves DRED enabled.
fn read_legacy_fec_env() -> bool {
match std::env::var(LEGACY_FEC_ENV) {
Ok(v) => !v.is_empty() && v != "0" && v.to_ascii_lowercase() != "false",
Err(_) => false,
}
}
/// Opus encoder implementing `AudioEncoder`.
///
/// Operates at 48 kHz mono. Supports frame sizes of 20 ms (960 samples)
/// and 40 ms (1920 samples).
/// Operates at 48 kHz mono. Supports 20 ms and 40 ms frames via the active
/// `QualityProfile`.
pub struct OpusEncoder {
inner: Encoder,
codec_id: CodecId,
frame_duration_ms: u8,
/// When `true`, revert to the Phase 0 behavior: inband FEC Mode1, DRED
/// disabled, no loss floor. Captured at construction time and not
/// re-read mid-call.
legacy_fec_mode: bool,
}
// SAFETY: OpusEncoder is only used via `&mut self` methods. The inner
@@ -35,28 +97,80 @@ impl OpusEncoder {
let encoder = Encoder::new(Channels::Mono, SampleRate::Hz48000, Application::Voip)
.map_err(|e| CodecError::EncodeFailed(format!("opus encoder init: {e:?}")))?;
let legacy_fec_mode = read_legacy_fec_env();
if legacy_fec_mode {
warn!(
"AUDIO_USE_LEGACY_FEC active — reverting Opus encoder to Phase 0 \
behavior (inband FEC Mode1, no DRED)"
);
}
let mut enc = Self {
inner: encoder,
codec_id: profile.codec,
frame_duration_ms: profile.frame_duration_ms,
legacy_fec_mode,
};
enc.apply_bitrate(profile.codec)?;
enc.set_inband_fec(true);
enc.set_dtx(true);
// Voice signal type hint for better compression
// Common setup — bitrate, DTX, signal hint, complexity. These are
// identical regardless of the protection mode below.
enc.apply_bitrate(profile.codec)?;
enc.set_dtx(true);
enc.inner
.set_signal(Signal::Voice)
.map_err(|e| CodecError::EncodeFailed(format!("set signal: {e:?}")))?;
// Default complexity 7 — good quality/CPU trade-off for VoIP
enc.inner
.set_complexity(7)
.map_err(|e| CodecError::EncodeFailed(format!("set complexity: {e:?}")))?;
// Protection mode: DRED (Phase 1 default) or legacy inband FEC.
enc.apply_protection_mode(profile.codec)?;
Ok(enc)
}
/// Configure the protection mode for the active codec.
///
/// In DRED mode (default): disable inband FEC, set DRED duration for the
/// codec tier, clamp packet_loss to the 5% floor so DRED stays active.
///
/// In legacy mode: enable inband FEC Mode1 (Phase 0 behavior), leave
/// DRED and packet_loss at libopus defaults.
fn apply_protection_mode(&mut self, codec: CodecId) -> Result<(), CodecError> {
if self.legacy_fec_mode {
self.inner
.set_inband_fec(InbandFec::Mode1)
.map_err(|e| CodecError::EncodeFailed(format!("set inband FEC: {e:?}")))?;
// Leave DRED at 0 and packet_loss at default — matches Phase 0.
return Ok(());
}
// DRED path: disable the overlapping inband FEC, enable DRED with
// per-profile duration, floor packet_loss so DRED emits.
self.inner
.set_inband_fec(InbandFec::Off)
.map_err(|e| CodecError::EncodeFailed(format!("set inband FEC off: {e:?}")))?;
let dred_frames = dred_duration_for(codec);
self.inner
.set_dred_duration(dred_frames)
.map_err(|e| CodecError::EncodeFailed(format!("set DRED duration: {e:?}")))?;
self.inner
.set_packet_loss(DRED_LOSS_FLOOR_PCT)
.map_err(|e| CodecError::EncodeFailed(format!("set packet loss floor: {e:?}")))?;
debug!(
codec = ?codec,
dred_frames,
dred_ms = dred_frames as u32 * 10,
loss_floor_pct = DRED_LOSS_FLOOR_PCT,
"opus encoder: DRED enabled"
);
Ok(())
}
fn apply_bitrate(&mut self, codec: CodecId) -> Result<(), CodecError> {
let bps = codec.bitrate_bps();
self.inner
@@ -80,10 +194,36 @@ impl OpusEncoder {
/// Hint the encoder about expected packet loss percentage (0-100).
///
/// Higher values cause the encoder to use more redundancy to survive
/// packet loss, at the expense of slightly higher bitrate.
/// In DRED mode, the value is floored at `DRED_LOSS_FLOOR_PCT` so the
/// encoder never drops DRED emission even on a perfect network. Real
/// loss measurements from the quality adapter override upward.
///
/// In legacy mode, the value is passed through unchanged (min 0, max 100).
pub fn set_expected_loss(&mut self, loss_pct: u8) {
let _ = self.inner.set_packet_loss(loss_pct.min(100));
let clamped = if self.legacy_fec_mode {
loss_pct.min(100)
} else {
loss_pct.max(DRED_LOSS_FLOOR_PCT).min(100)
};
let _ = self.inner.set_packet_loss(clamped);
}
/// Set the DRED duration in 10 ms frame units (0 disables, max 104).
///
/// No-op in legacy mode. Normally driven automatically by the active
/// quality profile via `apply_protection_mode`; this setter exists for
/// tests and for the rare case where a caller needs to override the
/// per-profile default.
pub fn set_dred_duration(&mut self, frames: u8) {
if self.legacy_fec_mode {
return;
}
let _ = self.inner.set_dred_duration(frames.min(104));
}
/// Test/introspection accessor: whether legacy FEC mode is active.
pub fn is_legacy_fec_mode(&self) -> bool {
self.legacy_fec_mode
}
}
@@ -117,6 +257,9 @@ impl AudioEncoder for OpusEncoder {
self.codec_id = profile.codec;
self.frame_duration_ms = profile.frame_duration_ms;
self.apply_bitrate(profile.codec)?;
// Refresh DRED duration for the new tier. apply_protection_mode
// is idempotent and handles the legacy-vs-DRED branch correctly.
self.apply_protection_mode(profile.codec)?;
Ok(())
}
other => Err(CodecError::UnsupportedTransition {
@@ -133,12 +276,18 @@ impl AudioEncoder for OpusEncoder {
}
fn set_inband_fec(&mut self, enabled: bool) {
// opusic-c replaces the audiopus bool with an enum that distinguishes
// Mode1 (classical LBRR, equivalent to libopus 1.3's inband FEC) and
// Mode2 (newer, higher-quality variant added in 1.5). Phase 0 preserves
// pre-swap behavior by using Mode1, which is the direct equivalent of
// audiopus's `set_inband_fec(true)`. Phase 1 flips this to Off when
// DRED is enabled.
// In DRED mode, ignore external requests to re-enable inband FEC —
// running both mechanisms wastes bitrate on overlapping protection
// and opusic-c's own docs recommend disabling inband FEC when DRED
// is on. Trait callers that genuinely want classical FEC should set
// `AUDIO_USE_LEGACY_FEC=1` and re-create the encoder.
if !self.legacy_fec_mode {
debug!(
enabled,
"set_inband_fec ignored: DRED mode is active (set AUDIO_USE_LEGACY_FEC to revert)"
);
return;
}
let mode = if enabled { InbandFec::Mode1 } else { InbandFec::Off };
let _ = self.inner.set_inband_fec(mode);
}
@@ -174,9 +323,8 @@ mod tests {
#[test]
fn encoder_roundtrip_silence() {
use crate::opus_dec::OpusDecoder;
let mut enc = OpusEncoder::new(QualityProfile::GOOD).unwrap();
let mut dec = OpusDecoder::new(QualityProfile::GOOD).unwrap();
let mut dec = crate::opus_dec::OpusDecoder::new(QualityProfile::GOOD).unwrap();
let pcm_in = vec![0i16; 960]; // 20 ms silence
let mut encoded = vec![0u8; 512];
let n = enc.encode(&pcm_in, &mut encoded).unwrap();
@@ -185,4 +333,133 @@ mod tests {
let samples = dec.decode(&encoded[..n], &mut pcm_out).unwrap();
assert_eq!(samples, 960);
}
// ─── Phase 1 — DRED duration policy ─────────────────────────────────────
#[test]
fn dred_duration_for_studio_tiers_is_100ms() {
assert_eq!(dred_duration_for(CodecId::Opus32k), 10);
assert_eq!(dred_duration_for(CodecId::Opus48k), 10);
assert_eq!(dred_duration_for(CodecId::Opus64k), 10);
}
#[test]
fn dred_duration_for_normal_tiers_is_200ms() {
assert_eq!(dred_duration_for(CodecId::Opus16k), 20);
assert_eq!(dred_duration_for(CodecId::Opus24k), 20);
}
#[test]
fn dred_duration_for_degraded_tier_is_500ms() {
assert_eq!(dred_duration_for(CodecId::Opus6k), 50);
}
#[test]
fn dred_duration_for_codec2_is_zero() {
assert_eq!(dred_duration_for(CodecId::Codec2_3200), 0);
assert_eq!(dred_duration_for(CodecId::Codec2_1200), 0);
assert_eq!(dred_duration_for(CodecId::ComfortNoise), 0);
}
// ─── Phase 1 — Legacy escape hatch ──────────────────────────────────────
/// By default (env var unset), legacy mode is off.
///
/// This test does NOT manipulate the environment to avoid flakiness
/// when the full suite runs in parallel. It only asserts on a freshly
/// created encoder in the ambient environment.
#[test]
fn default_mode_is_dred_not_legacy() {
// SAFETY: only run if the ambient env hasn't set the var externally.
if std::env::var(LEGACY_FEC_ENV).is_ok() {
return; // don't assert — someone set the env for a reason.
}
let enc = OpusEncoder::new(QualityProfile::GOOD).unwrap();
assert!(!enc.is_legacy_fec_mode());
}
// ─── Phase 1 — Behavioral regression: roundtrip still works ─────────────
#[test]
fn dred_mode_roundtrip_voice_pattern() {
// Use a realistic voice-like input (sine wave at speech frequencies)
// so the encoder emits meaningful DRED data rather than trivially
// compressible silence.
let mut enc = OpusEncoder::new(QualityProfile::GOOD).unwrap();
let mut dec = crate::opus_dec::OpusDecoder::new(QualityProfile::GOOD).unwrap();
let mut total_encoded_bytes = 0usize;
// Run 50 frames (1 second) so DRED fills up and starts emitting.
for frame_idx in 0..50 {
let pcm_in: Vec<i16> = (0..960)
.map(|i| {
let t = (frame_idx * 960 + i) as f64 / 48_000.0;
(8000.0 * (2.0 * std::f64::consts::PI * 300.0 * t).sin()) as i16
})
.collect();
let mut encoded = vec![0u8; 512];
let n = enc.encode(&pcm_in, &mut encoded).unwrap();
assert!(n > 0);
total_encoded_bytes += n;
let mut pcm_out = vec![0i16; 960];
let samples = dec.decode(&encoded[..n], &mut pcm_out).unwrap();
assert_eq!(samples, 960);
}
// Effective bitrate after 1 second of encoding.
// Opus 24k base + ~1 kbps DRED ≈ 25 kbps ≈ 3125 bytes/sec.
// Allow generous headroom (2000 lower bound, 8000 upper bound) —
// this is a behavioral regression check, not a tight bitrate assertion.
// The exact value is printed with --nocapture for diagnostic use.
eprintln!(
"[phase1 bitrate probe] legacy_fec_mode={} total_encoded={} bytes/sec",
enc.is_legacy_fec_mode(),
total_encoded_bytes
);
assert!(
total_encoded_bytes > 2000,
"encoder output too small: {total_encoded_bytes} bytes/sec (DRED likely not emitting)"
);
assert!(
total_encoded_bytes < 8000,
"encoder output too large: {total_encoded_bytes} bytes/sec"
);
}
// ─── Phase 1 — set_profile updates DRED duration on tier switch ─────────
#[test]
fn profile_switch_refreshes_dred_duration() {
// Start on GOOD (Opus 24k, DRED 20 frames), switch to DEGRADED
// (Opus 6k, DRED 50 frames). The encoder should accept both profile
// changes without error. We can't directly observe the DRED duration
// inside libopus, but apply_protection_mode returns Ok for both.
let mut enc = OpusEncoder::new(QualityProfile::GOOD).unwrap();
assert_eq!(enc.codec_id, CodecId::Opus24k);
enc.set_profile(QualityProfile::DEGRADED).unwrap();
assert_eq!(enc.codec_id, CodecId::Opus6k);
enc.set_profile(QualityProfile::STUDIO_64K).unwrap();
assert_eq!(enc.codec_id, CodecId::Opus64k);
}
// ─── Phase 1 — Trait set_inband_fec is a no-op in DRED mode ─────────────
#[test]
fn set_inband_fec_noop_in_dred_mode() {
if std::env::var(LEGACY_FEC_ENV).is_ok() {
return;
}
let mut enc = OpusEncoder::new(QualityProfile::GOOD).unwrap();
// Should not error, should not re-enable inband FEC internally.
enc.set_inband_fec(true);
// We can't directly query libopus's inband FEC state through opusic-c,
// but the call must not panic and the encoder must still work.
let pcm_in = vec![0i16; 960];
let mut encoded = vec![0u8; 512];
let n = enc.encode(&pcm_in, &mut encoded).unwrap();
assert!(n > 0);
}
}