The original Phase 3b landed on wzp-client/CallDecoder and Phase 3c
landed on wzp-android/src/engine.rs. Both of those are DEAD CODE on
feat/desktop-audio-rewrite: the legacy Kotlin app in android/app/ is
not built by the Tauri mobile pipeline, and the Tauri engine bypasses
CallDecoder by calling wzp_codec::create_decoder directly.
The live Android call engine lives at desktop/src-tauri/src/engine.rs
with two `pub async fn start<F>` functions — one cfg-gated on Android
(Oboe via wzp-native) and one for desktop (CPAL). Both recv tasks
were using `let mut decoder = wzp_codec::create_decoder(...)` which
returns `Box<dyn AudioDecoder>` and doesn't expose the inherent
`reconstruct_from_dred` method.
Changes:
New helper struct `DredRecvState` at the top of engine.rs, wrapping:
- DredDecoderHandle (libopus DRED side-channel parser)
- DredState scratch (for parse_into)
- DredState last_good (cached valid state, swapped on success)
- last_good_seq: Option<u16> (DRED anchor sequence)
- expected_seq: Option<u16> (for gap detection)
- dred_reconstructions / classical_plc_invocations counters
With three methods:
- ingest_opus(seq, payload): parse DRED, swap on success
- fill_gap_to(decoder, current_seq, frame_samples, scratch, emit):
detect gap back from expected_seq, reconstruct each missing
frame via DRED if state covers it, fall through to classical
decoder.decode_lost() when it doesn't. Calls emit() once per
frame with a slice the caller uses for AGC + playout write.
- reset_on_profile_switch(): invalidate tracking when codec changes
Both recv tasks (Android @ ~line 297 and desktop @ ~line 907):
- Decoder type changed from `Box<dyn AudioDecoder>` via
`wzp_codec::create_decoder` to concrete `AdaptiveDecoder::new(profile)`
so we can call the inherent reconstruct_from_dred method.
- Added `use wzp_proto::traits::AudioDecoder;` at the top of
engine.rs to bring decode/decode_lost/set_profile trait methods
into scope on the concrete type.
- New `current_profile` local alongside `current_codec` (used for
frame_duration lookups that drive the DRED sample offset math).
- On codec/profile switch, call dred_recv.reset_on_profile_switch()
because the cached DRED state is tied to the old profile's
frame rate.
- For each arriving Opus source packet:
1. dred_recv.ingest_opus(seq, payload) — parse DRED
2. dred_recv.fill_gap_to(...) — detect gap and reconstruct
missing frames, each emitted through a closure that does
AGC + playout write (wzp_native on Android, playout_ring
on desktop)
3. Normal decoder.decode() fallthrough for the current packet
(unchanged)
- Codec2 packets skip the DRED path entirely (is_opus() gate) —
libopus can't reconstruct Codec2 audio.
Ordering invariant: gap reconstruction writes to playout BEFORE the
current packet's decoded audio, preserving temporal order since the
playout ring is FIFO. The closure captures the `spk_muted` flag once
before the gap loop to avoid mid-gap-fill state changes.
Kept `crates/wzp-android/src/engine.rs` and `crates/wzp-android/src/
stats.rs` from the earlier Phase 3c commit as-is — they're dead code
on feat/desktop-audio-rewrite but harmless, and deleting them would
diverge this branch from an independently-useful intermediate state.
The old Phase 3c commit (505a834) stays as historical reference.
Verification:
- cargo check -p wzp-codec -p wzp-client -p wzp-relay: 0 errors
- cargo check -p wzp-desktop: only pre-existing `tauri::generate_context!()`
panic on missing ../dist (Vite output not built on host) — no Rust
compile errors from our changes
- cargo test -p wzp-codec --lib: 69 passing (unchanged)
- cargo test -p wzp-client --lib: 35 passing + 1 ignored (unchanged)
Next: scripts/build-tauri-android.sh to get the actual Tauri APK —
NOT build-and-notify.sh which builds the dead legacy android/app.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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