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Close the latency gap on the Android client with per-SoC decoder tuning, an event-driven decode loop, and full system integration. - Decoder selection: rank MediaCodecList decoders in Kotlin (hardware/vendor preferred, software avoided, FEATURE_LowLatency probed) and create the chosen one by name. Per-SoC low-latency keys gated on the codec-name prefix: Qualcomm picture-order + low-latency, Exynos (also Google Tensor), Amlogic, HiSilicon; MediaTek vdec-lowlatency set unconditionally. operating-rate = MAX (Qualcomm) vs priority = 0 (else) are mutually exclusive. NVIDIA/Rockchip/Realtek have no vendor key — covered by ranking + the standard low-latency key. - Async decode loop: AMediaCodec async-notify replaces the poll loop, presenting a decoded frame the instant it is ready instead of waiting out a poll interval. Behind USE_ASYNC_DECODE with the synchronous loop kept for A/B during bring-up. - System integration: Wi-Fi FULL_LOW_LATENCY lock and HDMI ALLM (setPreferMinimalPostProcessing) for the stream's lifetime; game_mode_config.xml opting out of OEM downscaling / FPS overrides. - Pipeline: boost the data-plane pump + audio thread priorities, AAudio usage=Game, DSCP marking on by default on Android, ADPF setPreferPowerEfficiency(false), and setFrameRateWithChangeStrategy(ALWAYS) to force the HDMI mode switch on TV. - lowLatencyMode master toggle (default on) as the escape hatch; the stats HUD now shows the resolved decoder name. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
punktfunk-core
The shared protocol core — the one place where punktfunk's transport, forward error correction, and crypto live. It's linked into the host and every native client, so there's exactly one implementation of the wire format everywhere.
Written in Rust with no async on the per-frame path (native threads only). It exposes both a normal Rust API and a stable, versioned C ABI, so the Swift and Kotlin clients — and any C embedder — link the same code as the Rust ones.
What's in here
- Transport & session (
session.rs,transport/,packet.rs) — thepunktfunk/1data plane over raw UDP: packetization, reassembly (with attacker-bounded limits), pacing, and socket tuning. - FEC (
fec/) — the wall-breaker. Two codes:- GF(2⁸) classic Reed–Solomon with the Cauchy generator matrix — byte-identical to the
nanorslibrary Moonlight uses, so our parity is decodable by a stock Moonlight client. - GF(2¹⁶) Leopard-RS (SIMD, O(n log n)) — up to 65535 shards/block, which removes the ~1 Gbps
FEC ceiling.
punktfunk/1negotiates this one.
- GF(2⁸) classic Reed–Solomon with the Cauchy generator matrix — byte-identical to the
- Crypto (
crypto.rs) — AES-128-GCM session encryption with per-direction nonce salts and sequence-as-AAD; SPAKE2 PIN pairing lives behind thequicfeature. - QUIC control plane (
quic.rs,client.rs, featurequic) — the Hello/Welcome/Start handshake, cert pinning/TOFU, reverse audio, and the embeddableNativeClientconnector. This is the only placetokio/quinnare allowed; the feature is off by default so the core stays runtime-free. - C ABI (
abi.rs) — the versioned surface (punktfunk_abi_version(),PunktfunkConfigcarrying its ownstruct_size) that generatesinclude/punktfunk_core.hvia cbindgen at build time.
Build outputs
The crate builds three ways at once (crate-type = ["lib", "cdylib", "staticlib"]):
| Output | Used by |
|---|---|
lib (rlib) |
the host, probe, and tools link it as a normal Rust crate |
cdylib (.so/.dylib) |
the Swift / Kotlin clients via the C ABI |
staticlib (.a) |
the C test harness and static embedding |
Test
cargo test -p punktfunk-core # unit + proptest + loopback
cargo run -p loss-harness # FEC loss-resilience sweep (no network needed)
bash crates/punktfunk-core/tests/c/run.sh # standalone C-ABI link + round-trip proof
Design invariants (do not regress)
- One core, linked everywhere — protocol/FEC/crypto live only here, behind the stable C ABI.
- No async on the hot path — the per-frame pipeline is native threads only;
quic(tokio/quinn) is control-plane only, feature-gated, off by default. - Security hardening stays intact — the reassembler bounds attacker-controlled fields before
allocating; AES-GCM keeps per-direction nonce salts + seq-as-AAD; the ABI checks
struct_size. Regression tests exist — keep them green.
Related
punktfunk-host— the streaming host built on this core- Clients — the apps that link this core over the C ABI (or directly, in Rust)
design/implementation-plan.md— why GF(2¹⁶) FEC, the latency budget, and the architecture thesis