perf(android): low-latency decode overhaul — vendor keys, async loop, system tuning

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>

clients/android/kit/src/main/kotlin/io/unom/punktfunk/kit/NativeBridge.kt

@@ -104,14 +104,40 @@ object NativeBridge {
     external fun nativeWakeOnLan(macsCsv: String, lastIp: String): Boolean
 
     /**
-     * Start the HEVC decode thread rendering onto [surface] (a SurfaceView's surface). Decode runs
-     * entirely in Rust (NDK AMediaCodec → ANativeWindow) — no per-frame JNI. No-op if already started.
+     * The MediaCodec MIME the host resolved for this session (`"video/hevc"` / `"video/avc"` /
+     * `"video/av01"`), or `""` on a `0` handle. Kotlin ranks `MediaCodecList` decoders for this
+     * MIME (see [io.unom.punktfunk.kit.VideoDecoders]) before [nativeStartVideo]. Cheap; UI-safe.
      */
-    external fun nativeStartVideo(handle: Long, surface: android.view.Surface)
+    external fun nativeVideoMime(handle: Long): String
+
+    /**
+     * Start the decode thread rendering onto [surface] (a SurfaceView's surface). Decode runs
+     * entirely in Rust (NDK AMediaCodec → ANativeWindow) — no per-frame JNI. [decoderName] is the
+     * decoder Kotlin ranked from `MediaCodecList` (`""` = let the platform resolve the default for
+     * the MIME); [lowLatencyMode] is the user's master toggle (default on → aggressive per-SoC
+     * tuning; off → conservative); [lowLatencyFeature] is whether [decoderName] advertised
+     * `FEATURE_LowLatency` (HUD label only). [isTv] drives an active HDMI mode switch to the stream
+     * refresh on TV boxes (vs. the softer seamless hint on phones). No-op if already started.
+     */
+    external fun nativeStartVideo(
+        handle: Long,
+        surface: android.view.Surface,
+        decoderName: String,
+        lowLatencyMode: Boolean,
+        lowLatencyFeature: Boolean,
+        isTv: Boolean,
+    )
 
     /** Stop + join the decode thread without closing the session. No-op on `0`. */
     external fun nativeStopVideo(handle: Long)
 
+    /**
+     * The resolved decoder identity for the HUD, e.g. `c2.qti.avc.decoder · low-latency`, or `""`
+     * before the decode thread has resolved one. One-shot (fixed for the session); poll once after
+     * the HUD appears.
+     */
+    external fun nativeVideoDecoderLabel(handle: Long): String
+
     /**
      * Drain ~1 s of live decode stats for the on-stream HUD, or `null` when no decode thread runs.
      * Returns 18 doubles (unified stats spec, `design/stats-unification.md`):

clients/android/kit/src/main/kotlin/io/unom/punktfunk/kit/VideoDecoders.kt

@@ -0,0 +1,85 @@
+package io.unom.punktfunk.kit
+
+import android.media.MediaCodecInfo.CodecCapabilities
+import android.media.MediaCodecList
+import android.os.Build
+
+/** The decoder Kotlin ranked for a MIME, handed to [NativeBridge.nativeStartVideo]. */
+data class DecoderChoice(val name: String, val lowLatencyFeature: Boolean)
+
+/**
+ * Rank the platform's `MediaCodecList` decoders for a video MIME and pick the best one for
+ * low-latency streaming, the way Moonlight-Android does. There is no NDK `MediaCodecList`, so this
+ * enumeration must live on the Kotlin (framework) side; Rust then creates the chosen decoder by
+ * name (`AMediaCodec_createCodecByName`) and derives the per-SoC vendor low-latency keys from it.
+ *
+ * Ranking (best first): hardware over software; a real SoC-vendor decoder (Qualcomm/Amlogic/…) over
+ * the generic AOSP software fallback; a decoder advertising `FEATURE_LowLatency` over one that
+ * doesn't. Known-bad software decoders (`omx.google.*`, `c2.android.*`, Qualcomm/Samsung SW HEVC)
+ * are dropped outright — matching Moonlight's blacklist.
+ */
+object VideoDecoders {
+    /** Decoder-name prefixes/names we never want, mirroring Moonlight's blacklist. */
+    private val BLOCKED_PREFIXES = listOf("omx.google.", "c2.android.", "avcdecoder", "omx.ffmpeg.")
+    private val BLOCKED_EXACT = listOf("omx.qcom.video.decoder.hevcswvdec", "omx.sec.hevc.sw.dec")
+
+    /**
+     * Real SoC-vendor decoder prefixes we prefer over the generic AOSP fallback, covering the common
+     * targets: Qualcomm Snapdragon and MediaTek (most phones + many TV boxes), Samsung Exynos (+
+     * Google Tensor, whose decoder is `c2.exynos.*`), NVIDIA Tegra (Shield TV), Amlogic / Rockchip /
+     * Realtek (TV boxes & smart TVs), and HiSilicon Kirin (older Huawei).
+     */
+    private val VENDOR_PREFIXES = listOf(
+        "omx.qcom", "c2.qti",
+        "omx.mtk", "c2.mtk",
+        "omx.exynos", "c2.exynos",
+        "omx.nvidia", "c2.nvidia",
+        "omx.amlogic", "c2.amlogic",
+        "omx.rk", "c2.rk",
+        "omx.realtek", "c2.realtek",
+        "omx.hisi", "c2.hisi",
+    )
+
+    /**
+     * Pick the best decoder for [mime] (`"video/hevc"` / `"video/avc"` / `"video/av01"`), or `null`
+     * to let the platform resolve its default. Enumerates once — call at stream start.
+     */
+    fun pickDecoder(mime: String): DecoderChoice? {
+        if (mime.isEmpty()) return null
+        val infos = runCatching { MediaCodecList(MediaCodecList.REGULAR_CODECS).codecInfos }
+            .getOrNull() ?: return null
+
+        var bestName: String? = null
+        var bestLowLatency = false
+        var bestScore = Int.MIN_VALUE
+        for (info in infos) {
+            if (info.isEncoder) continue
+            val name = info.name
+            val lower = name.lowercase()
+            if (BLOCKED_PREFIXES.any { lower.startsWith(it) } || lower in BLOCKED_EXACT) continue
+            val caps = runCatching { info.getCapabilitiesForType(mime) }.getOrNull() ?: continue
+
+            val hardware = if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q) {
+                info.isHardwareAccelerated
+            } else {
+                // Pre-Q heuristic: the software decoders are the ones we can name (already blocked
+                // above), so anything surviving the blacklist is treated as hardware.
+                true
+            }
+            val lowLatency = Build.VERSION.SDK_INT >= Build.VERSION_CODES.R &&
+                runCatching { caps.isFeatureSupported(CodecCapabilities.FEATURE_LowLatency) }
+                    .getOrDefault(false)
+            val vendor = VENDOR_PREFIXES.any { lower.startsWith(it) }
+
+            val score = (if (hardware) 100 else 0) +
+                (if (vendor) 40 else 0) +
+                (if (lowLatency) 20 else 0)
+            if (score > bestScore) {
+                bestScore = score
+                bestName = name
+                bestLowLatency = lowLatency
+            }
+        }
+        return bestName?.let { DecoderChoice(it, bestLowLatency) }
+    }
+}