diff --git a/app/static/js/services/unifiedMidiRouter.js b/app/static/js/services/unifiedMidiRouter.js
new file mode 100644
index 0000000..b03d829
--- /dev/null
+++ b/app/static/js/services/unifiedMidiRouter.js
@@ -0,0 +1,128 @@
+// SonicForge Unified MIDI Router
+// Mọi nguồn MIDI (keybed preview, timeline scheduler, hardware MIDI) → chuẩn
+// hóa UnifiedMidiEvent → UnifiedMidiRouter → engine theo trackId. Một điểm
+// dispatch duy nhất: activeVoiceTracker đếm note-on/off đúng (hết stuck
+// notes), panicAllNotesOff() quét toàn bộ voice khi đổi instrument/engine
+// giữa chừng. Chưa nối vào app (T5–T7 sẽ đăng ký engine + dispatch).
+window.SonicUnifiedMidiRouter = window.SonicUnifiedMidiRouter || {};
+
+(function () {
+    var COMMAND_NOTE_ON = 0x90;
+    var COMMAND_NOTE_OFF = 0x80;
+    var COMMAND_CC = 0xB0;
+
+    // Pitch: ép int 0-127 (spec "pitch clamp 0-127").
+    function clampPitch(pitch) {
+        pitch = Math.round(Number(pitch) || 0);
+        if (pitch < 0) return 0;
+        if (pitch > 127) return 127;
+        return pitch;
+    }
+
+    // Velocity: float 0-1 (vd 100/127) hoặc int → ép int 1-127 (note-on);
+    // note-off velocity = 0. Spec "velocity normalize float→int".
+    function normalizeVelocity(velocity, isNoteOn) {
+        var v = Number(velocity);
+        if (!isFinite(v)) v = 0;
+        if (v > 0 && v <= 1) v = v * 127;
+        v = Math.round(v);
+        if (v < 0) v = 0;
+        if (v > 127) v = 127;
+        if (isNoteOn && v <= 0) v = 1;
+        return v;
+    }
+
+    function UnifiedMidiRouter() {
+        this.engineRegistry = new Map(); // trackId → TrackInstrument
+        // activeVoiceTracker: key `${trackId}_${channel}_${pitch}` → { count, engine }.
+        // (Spec dùng `${channel}_${pitch}`; thêm trackId vì engine theo track —
+        // 2 track cùng channel+pitch phải đếm riêng, không lệch voice.)
+        this._voices = new Map();
+    }
+
+    // Đăng ký engine cho track (null = xóa). Đổi instrument → registerEngine
+    // track mới; panic trước đó để không sót voice cũ.
+    UnifiedMidiRouter.prototype.registerEngine = function (trackId, engine) {
+        if (trackId === undefined || trackId === null) return;
+        if (engine) this.engineRegistry.set(trackId, engine);
+        else this.engineRegistry.delete(trackId);
+    };
+
+    // Dispatch 1 event từ mọi nguồn. Không ném — voice tracker luôn đếm đúng.
+    // Trả true nếu event là note (đã route/count), false nếu không xử lý.
+    UnifiedMidiRouter.prototype.dispatchMidiEvent = function (evt) {
+        if (!evt) return false;
+        var trackId = evt.trackId;
+        var engine = (trackId !== undefined && trackId !== null) ? this.engineRegistry.get(trackId) : null;
+        var channel = Math.round(Number(evt.channel) || 0);
+        if (channel < 0) channel = 0;
+        if (channel > 15) channel = 15;
+        var pitch = clampPitch(evt.pitch);
+        var cmd = Number(evt.command);
+        var key = trackId + '_' + channel + '_' + pitch;
+
+        var isNoteOn = (cmd === COMMAND_NOTE_ON);
+        var isNoteOff = (cmd === COMMAND_NOTE_OFF) || (cmd === COMMAND_NOTE_ON && !Number(evt.velocity));
+
+        if (isNoteOn) {
+            var vel = normalizeVelocity(evt.velocity, true);
+            var cur = this._voices.get(key);
+            if (!cur) {
+                cur = { count: 0, engine: engine };
+                this._voices.set(key, cur);
+            }
+            cur.engine = engine;
+            cur.count += 1;
+            // Chỉ trigger âm ở note-on đầu tiên; các note-on trùng key chỉ tăng
+            // count (sustain lặp) — note-off cuối cùng mới tắt voice.
+            if (cur.count === 1 && engine && engine.playNote) {
+                try { engine.playNote(pitch, vel, evt.durationMs || 500); } catch (e) {}
+            }
+            return true;
+        }
+
+        if (isNoteOff) {
+            var cur2 = this._voices.get(key);
+            if (cur2 && cur2.count > 0) {
+                cur2.count -= 1;
+                var eng2 = cur2.engine;
+                if (cur2.count <= 0) {
+                    this._voices.delete(key);
+                    if (eng2 && eng2.noteOff) {
+                        try { eng2.noteOff(pitch); } catch (e) {}
+                    }
+                }
+            }
+            return true;
+        }
+
+        return false; // CC / unknown
+    };
+
+    // All Notes Off: quét voice tracker, gửi note-off cho engine sở hữu từng
+    // voice, xóa tracker. Gọi khi dừng playback / đổi instrument giữa chừng.
+    UnifiedMidiRouter.prototype.panicAllNotesOff = function () {
+        var self = this;
+        this._voices.forEach(function (v, key) {
+            if (v.engine && v.engine.noteOff) {
+                var parts = key.split('_');
+                var pitch = parseInt(parts[parts.length - 1], 10);
+                try { v.engine.noteOff(pitch); } catch (e) {}
+            }
+        });
+        this._voices.clear();
+    };
+
+    // Số voice active cho 1 (track, channel, pitch) — test/debug.
+    UnifiedMidiRouter.prototype.activeVoiceCount = function (trackId, channel, pitch) {
+        var cur = this._voices.get(trackId + '_' + channel + '_' + pitch);
+        return cur ? cur.count : 0;
+    };
+
+    window.SonicUnifiedMidiRouter = {
+        UnifiedMidiRouter: UnifiedMidiRouter,
+        COMMAND_NOTE_ON: COMMAND_NOTE_ON,
+        COMMAND_NOTE_OFF: COMMAND_NOTE_OFF,
+        COMMAND_CC: COMMAND_CC
+    };
+})();
diff --git a/tests/unified_midi_router.test.js b/tests/unified_midi_router.test.js
new file mode 100644
index 0000000..556f0d3
--- /dev/null
+++ b/tests/unified_midi_router.test.js
@@ -0,0 +1,57 @@
+// T4 test: node tests/unified_midi_router.test.js
+// Router chưa nối app — test độc lập qua window stub.
+'use strict';
+global.window = {};
+require('../app/static/js/services/unifiedMidiRouter.js');
+const R = global.window.SonicUnifiedMidiRouter;
+const assert = require('assert');
+
+const calls = [];
+function makeEngine() {
+    return {
+        playNote(pitch, vel, dur) { calls.push(['on', pitch, vel, dur]); },
+        noteOff(pitch) { calls.push(['off', pitch]); }
+    };
+}
+
+// 1) pitch clamp
+const r = new R.UnifiedMidiRouter();
+const eng = makeEngine();
+r.registerEngine('t1', eng);
+r.dispatchMidiEvent({ trackId: 't1', channel: 0, command: R.COMMAND_NOTE_ON, pitch: 200, velocity: 1, sourceType: 'TEST' });
+assert.deepStrictEqual(calls[0], ['on', 127, 127, 500], 'pitch clamp 200->127');
+r.dispatchMidiEvent({ trackId: 't1', channel: 0, command: R.COMMAND_NOTE_OFF, pitch: -3 });
+assert.strictEqual(calls.length, 1, 'note-off khong co voice -> khong goi engine (pitch clamp khong crash)');
+
+// 2) velocity normalize float->int (100/127 -> 100, 0.5 -> 64)
+r.dispatchMidiEvent({ trackId: 't1', channel: 1, command: R.COMMAND_NOTE_ON, pitch: 60, velocity: 100 / 127 });
+assert.deepStrictEqual(calls[1], ['on', 60, 100, 500], 'velocity 100/127 -> 100');
+r.dispatchMidiEvent({ trackId: 't1', channel: 1, command: R.COMMAND_NOTE_ON, pitch: 61, velocity: 0.5 });
+assert.deepStrictEqual(calls[2], ['on', 61, 64, 500], 'velocity 0.5 -> 64');
+
+// 3) tracker đếm đúng: 2 note-on trùng key -> 1 playNote; off cuối mới tắt
+r.dispatchMidiEvent({ trackId: 't1', channel: 2, command: R.COMMAND_NOTE_ON, pitch: 64, velocity: 100 });
+r.dispatchMidiEvent({ trackId: 't1', channel: 2, command: R.COMMAND_NOTE_ON, pitch: 64, velocity: 100 });
+assert.strictEqual(r.activeVoiceCount('t1', 2, 64), 2, '2 note-on count=2');
+const onCalls = calls.filter(c => c[0] === 'on' && c[1] === 64).length;
+assert.strictEqual(onCalls, 1, 'trung key chi play 1 lan');
+r.dispatchMidiEvent({ trackId: 't1', channel: 2, command: R.COMMAND_NOTE_OFF, pitch: 64 });
+assert.strictEqual(r.activeVoiceCount('t1', 2, 64), 1, '1 off -> count=1, chua noteOff');
+r.dispatchMidiEvent({ trackId: 't1', channel: 2, command: R.COMMAND_NOTE_OFF, pitch: 64 });
+assert.strictEqual(r.activeVoiceCount('t1', 2, 64), 0, 'off cuoi -> count=0');
+assert.deepStrictEqual(calls[calls.length - 1], ['off', 64], 'off cuoi moi noteOff');
+
+// 4) 2 track cùng channel+pitch đếm riêng (không lệch voice)
+const eng2 = makeEngine();
+r.registerEngine('t2', eng2);
+r.dispatchMidiEvent({ trackId: 't2', channel: 2, command: R.COMMAND_NOTE_ON, pitch: 64, velocity: 90 });
+assert.strictEqual(r.activeVoiceCount('t2', 2, 64), 1);
+assert.strictEqual(r.activeVoiceCount('t1', 2, 64), 0);
+
+// 5) panic clear: note đang giữ -> noteOff + tracker rỗng
+r.dispatchMidiEvent({ trackId: 't1', channel: 3, command: R.COMMAND_NOTE_ON, pitch: 72, velocity: 80 });
+r.panicAllNotesOff();
+assert.strictEqual(r.activeVoiceCount('t1', 3, 72), 0, 'panic xoa tracker');
+assert.deepStrictEqual(calls[calls.length - 1], ['off', 72], 'panic gui noteOff');
+
+console.log('unified_midi_router: ALL TESTS PASSED');