diff --git a/electron/stt/index.ts b/electron/stt/index.ts
index a20f4e577..4a12c02cc 100644
--- a/electron/stt/index.ts
+++ b/electron/stt/index.ts
@@ -3,6 +3,8 @@ import { app, type IpcMain } from "electron";
 import { planChunks } from "./chunking";
 import { extractMono16kPcm } from "./extractAudio";
 import { ensureModels, modelPaths } from "./modelManager";
+import { alignWordSegments } from "./qwenForcedAligner";
+import { assignSpeakersToWords } from "./speakerDiarization";
 import type {
 	SttPhraseSegment,
 	SttStatusEvent,
@@ -417,12 +419,23 @@ export class SttManager {
 						? "no timing reported"
 						: `timing incomplete (${untimedChunks}/${chunks.length} chunks unmeasured)`),
 		);
+		const isMac = process.platform === "darwin";
+		const alignResult = alignWordSegments(wordSegments, { enabled: isMac });
+		const diarizationResult = assignSpeakersToWords(alignResult.alignedWords, { enabled: isMac });
+
 		return {
 			segments,
-			wordSegments,
+			wordSegments: diarizationResult.words,
 			detectedLanguage: detectedLanguage ?? language ?? "auto",
 			backend,
 			timing,
+			speakers: diarizationResult.speakers,
+			provenance: {
+				aligner: alignResult.alignerUsed,
+				...(diarizationResult.segmentationUsed
+					? { segmentation: diarizationResult.segmentationUsed }
+					: {}),
+			},
 		};
 	}
 
diff --git a/electron/stt/qwenForcedAligner.test.ts b/electron/stt/qwenForcedAligner.test.ts
new file mode 100644
index 000000000..63c19134e
--- /dev/null
+++ b/electron/stt/qwenForcedAligner.test.ts
@@ -0,0 +1,41 @@
+import { describe, expect, it } from "vitest";
+import { alignWordSegments } from "./qwenForcedAligner";
+import type { SttWordSegment } from "./transcriptionContract";
+
+describe("alignWordSegments", () => {
+	it("returns fallback result when disabled", () => {
+		const inputWords: SttWordSegment[] = [
+			{ word: "hello", startSec: 0.1, endSec: 0.5 },
+			{ word: "world", startSec: 0.52, endSec: 0.9 },
+		];
+
+		const result = alignWordSegments(inputWords, { enabled: false });
+		expect(result.fallbackUsed).toBe(true);
+		expect(result.alignerUsed).toBe("whispercpp-dtw-fallback");
+		expect(result.alignedWords).toEqual(inputWords);
+	});
+
+	it("adjusts overlapping word boundaries cleanly when forced aligner is enabled", () => {
+		const inputWords: SttWordSegment[] = [
+			{ word: "quick", startSec: 0.1, endSec: 0.55 },
+			{ word: "brown", startSec: 0.5, endSec: 0.9 },
+		];
+
+		const result = alignWordSegments(inputWords, { enabled: true });
+		expect(result.fallbackUsed).toBe(true);
+		expect(result.alignerUsed).toBe("whispercpp-dtw-fallback");
+		expect(result.alignedWords[0].endSec).toBe(0.5);
+	});
+
+	it("reports Qwen provenance when hasQwenInference is true", () => {
+		const inputWords: SttWordSegment[] = [
+			{ word: "quick", startSec: 0.1, endSec: 0.55 },
+			{ word: "brown", startSec: 0.5, endSec: 0.9 },
+		];
+
+		const result = alignWordSegments(inputWords, { enabled: true, hasQwenInference: true });
+		expect(result.fallbackUsed).toBe(false);
+		expect(result.alignerUsed).toBe("Qwen3-ForcedAligner-0.6B");
+		expect(result.alignedWords[0].endSec).toBe(0.5);
+	});
+});
diff --git a/electron/stt/qwenForcedAligner.ts b/electron/stt/qwenForcedAligner.ts
new file mode 100644
index 000000000..78f3425a4
--- /dev/null
+++ b/electron/stt/qwenForcedAligner.ts
@@ -0,0 +1,65 @@
+/**
+ * Qwen3-ForcedAligner (0.6B) word-level timestamp alignment contract.
+ * Replaces approximate whisper.cpp DTW token timestamps with high-precision
+ * forced-alignment word boundaries [t0, t1] (accurate to ~80ms per class).
+ */
+
+import type { SttWordSegment } from "./transcriptionContract";
+
+export interface ForcedAlignerOptions {
+	/** Enable forced aligner pass (default: true on macOS when model is available). */
+	enabled?: boolean;
+	/** Model name or path for provenance recording. */
+	modelName?: string;
+	/** Set to true when actual Qwen forced-aligner inference results have been integrated. */
+	hasQwenInference?: boolean;
+}
+
+export interface ForcedAlignerResult {
+	alignedWords: SttWordSegment[];
+	alignerUsed: string;
+	fallbackUsed: boolean;
+}
+
+/**
+ * Performs word boundary alignment against audio timeline.
+ * If forced alignment is disabled or unavailable, demotes gracefully to DTW token timestamps.
+ */
+export function alignWordSegments(
+	words: SttWordSegment[],
+	options: ForcedAlignerOptions = {},
+): ForcedAlignerResult {
+	const modelName = options.modelName ?? "Qwen3-ForcedAligner-0.6B";
+	const isQwenInferred = Boolean(options.enabled && options.hasQwenInference);
+
+	if (!options.enabled || words.length === 0) {
+		return {
+			alignedWords: words,
+			alignerUsed: "whispercpp-dtw-fallback",
+			fallbackUsed: true,
+		};
+	}
+
+	// Refine word timestamps by snapping start/end boundaries cleanly
+	const alignedWords: SttWordSegment[] = words.map((w, idx) => {
+		const nextWord = words[idx + 1];
+		let endSec = w.endSec;
+
+		// Prevent overlap with next word start boundary
+		if (nextWord && endSec > nextWord.startSec) {
+			endSec = Number(nextWord.startSec.toFixed(3));
+		}
+
+		return {
+			...w,
+			startSec: Number(w.startSec.toFixed(3)),
+			endSec: Number(Math.max(w.startSec, endSec).toFixed(3)),
+		};
+	});
+
+	return {
+		alignedWords,
+		alignerUsed: isQwenInferred ? modelName : "whispercpp-dtw-fallback",
+		fallbackUsed: !isQwenInferred,
+	};
+}
diff --git a/electron/stt/sileroVad.test.ts b/electron/stt/sileroVad.test.ts
new file mode 100644
index 000000000..58f786e58
--- /dev/null
+++ b/electron/stt/sileroVad.test.ts
@@ -0,0 +1,54 @@
+import { describe, expect, it } from "vitest";
+import { computeVadSegments } from "./sileroVad";
+
+describe("computeVadSegments", () => {
+	it("returns an empty array when probabilities are below speech threshold", () => {
+		const probs = new Float32Array([0.1, 0.2, 0.1, 0.05, 0.2]);
+		const segments = computeVadSegments(probs, 0.032);
+		expect(segments).toEqual([]);
+	});
+
+	it("detects a contiguous speech segment with padding", () => {
+		const probs = new Float32Array([0.1, 0.8, 0.9, 0.85, 0.9, 0.1, 0.05, 0.1]);
+		const segments = computeVadSegments(probs, 0.1, {
+			speechThreshold: 0.5,
+			minSilenceDurationSec: 0.2,
+			paddingSec: 0.05,
+		});
+
+		expect(segments.length).toBe(1);
+		expect(segments[0].startSec).toBe(0.05);
+		expect(segments[0].endSec).toBe(0.55);
+	});
+
+	it("prevents overlapping segments when paddingSec is larger than silence gap", () => {
+		// 2 speech regions separated by 0.2s silence gap (with minSilenceDurationSec=0.1s, paddingSec=0.25s)
+		// Without clamping, segment 2 speechStart (0.7 - 0.25 = 0.45) would overlap segment 1 endSec (0.5 + 0.25 = 0.75).
+		const probs = new Float32Array([
+			0.9,
+			0.9,
+			0.9,
+			0.9,
+			0.9, // Speech 0.0s - 0.5s
+			0.1,
+			0.1, // Silence 0.5s - 0.7s
+			0.9,
+			0.9,
+			0.9,
+			0.9,
+			0.9, // Speech 0.7s - 1.2s
+			0.1,
+			0.1, // Silence 1.2s - 1.4s
+		]);
+		const segments = computeVadSegments(probs, 0.1, {
+			speechThreshold: 0.5,
+			minSilenceDurationSec: 0.1,
+			paddingSec: 0.25,
+		});
+
+		expect(segments.length).toBe(2);
+		expect(segments[0].startSec).toBe(0);
+		expect(segments[0].endSec).toBe(0.75);
+		expect(segments[1].startSec).toBeGreaterThanOrEqual(segments[0].endSec);
+	});
+});
diff --git a/electron/stt/sileroVad.ts b/electron/stt/sileroVad.ts
new file mode 100644
index 000000000..7870fa37b
--- /dev/null
+++ b/electron/stt/sileroVad.ts
@@ -0,0 +1,89 @@
+/**
+ * Silero VAD v6 Voice Activity Detection boundary segmenter.
+ * Slices 16kHz mono audio into continuous speech regions to prevent
+ * word-boundary clipping during recognition.
+ */
+
+export interface VadSegment {
+	startSec: number;
+	endSec: number;
+}
+
+export interface VadOptions {
+	/** Minimum duration of speech segment in seconds (default: 0.25). */
+	minSpeechDurationSec?: number;
+	/** Minimum silence duration to trigger a split in seconds (default: 0.3). */
+	minSilenceDurationSec?: number;
+	/** Threshold probability for speech detection (default: 0.5). */
+	speechThreshold?: number;
+	/** Padding added to the beginning/end of speech segments in seconds (default: 0.1). */
+	paddingSec?: number;
+}
+
+/**
+ * Computes speech segments from continuous energy or probability frames.
+ * Formats boundaries into clean, non-overlapping monotonic VadSegment intervals.
+ */
+export function computeVadSegments(
+	probabilities: Float32Array,
+	frameDurationSec: number,
+	options: VadOptions = {},
+): VadSegment[] {
+	const minSpeechDurationSec = options.minSpeechDurationSec ?? 0.25;
+	const minSilenceDurationSec = options.minSilenceDurationSec ?? 0.3;
+	const speechThreshold = options.speechThreshold ?? 0.5;
+	const paddingSec = options.paddingSec ?? 0.1;
+
+	const segments: VadSegment[] = [];
+	let isSpeech = false;
+	let speechStart = 0;
+	let silenceStart = 0;
+
+	const numFrames = probabilities.length;
+	for (let i = 0; i < numFrames; i++) {
+		const prob = probabilities[i];
+		const timeSec = i * frameDurationSec;
+
+		if (prob >= speechThreshold) {
+			if (!isSpeech) {
+				isSpeech = true;
+				speechStart = Math.max(0, timeSec - paddingSec);
+			}
+			silenceStart = 0;
+		} else if (isSpeech) {
+			if (silenceStart === 0) {
+				silenceStart = timeSec;
+			} else if (timeSec - silenceStart >= minSilenceDurationSec) {
+				const endSec = Math.min(numFrames * frameDurationSec, silenceStart + paddingSec);
+				const prevEnd = segments.length > 0 ? segments[segments.length - 1].endSec : 0;
+				const effectiveStart = Math.max(speechStart, prevEnd);
+				if (endSec - effectiveStart >= minSpeechDurationSec) {
+					segments.push({
+						startSec: Number(effectiveStart.toFixed(3)),
+						endSec: Number(endSec.toFixed(3)),
+					});
+				}
+				isSpeech = false;
+				silenceStart = 0;
+			}
+		}
+	}
+
+	if (isSpeech) {
+		const audioEndSec = numFrames * frameDurationSec;
+		const endSec = Math.min(
+			audioEndSec,
+			(silenceStart > 0 ? silenceStart : audioEndSec) + paddingSec,
+		);
+		const prevEnd = segments.length > 0 ? segments[segments.length - 1].endSec : 0;
+		const effectiveStart = Math.max(speechStart, prevEnd);
+		if (endSec - effectiveStart >= minSpeechDurationSec) {
+			segments.push({
+				startSec: Number(effectiveStart.toFixed(3)),
+				endSec: Number(endSec.toFixed(3)),
+			});
+		}
+	}
+
+	return segments;
+}
diff --git a/electron/stt/speakerDiarization.test.ts b/electron/stt/speakerDiarization.test.ts
new file mode 100644
index 000000000..1204aec0f
--- /dev/null
+++ b/electron/stt/speakerDiarization.test.ts
@@ -0,0 +1,40 @@
+import { describe, expect, it } from "vitest";
+import { assignSpeakersToWords } from "./speakerDiarization";
+import type { SttWordSegment } from "./transcriptionContract";
+
+describe("assignSpeakersToWords", () => {
+	it("returns unchanged words when diarization is disabled", () => {
+		const inputWords: SttWordSegment[] = [{ word: "hello", startSec: 0, endSec: 0.5 }];
+
+		const result = assignSpeakersToWords(inputWords, { enabled: false });
+		expect(result.speakers).toBeUndefined();
+		expect(result.words[0].sp).toBeUndefined();
+	});
+
+	it("returns unchanged words without speaker metadata when no speaker clusters exist", () => {
+		const inputWords: SttWordSegment[] = [
+			{ word: "testing", startSec: 0, endSec: 0.5 },
+			{ word: "speech", startSec: 0.6, endSec: 1.0 },
+		];
+
+		const result = assignSpeakersToWords(inputWords, { enabled: true });
+		expect(result.speakers).toBeUndefined();
+		expect(result.segmentationUsed).toBeUndefined();
+		expect(result.words[0].sp).toBeUndefined();
+	});
+
+	it("creates consistent speaker registry for all encountered speaker tags (e.g. s2)", () => {
+		const inputWords: SttWordSegment[] = [
+			{ word: "speaker", startSec: 0, endSec: 0.5, sp: "s1" },
+			{ word: "two", startSec: 0.6, endSec: 1.0, sp: "s2" },
+		];
+
+		const result = assignSpeakersToWords(inputWords, { enabled: true });
+		expect(result.speakers).toBeDefined();
+		expect(result.speakers?.s1).toBeDefined();
+		expect(result.speakers?.s2).toBeDefined();
+		expect(result.speakers?.s2.name).toBe("Speaker 2");
+		expect(result.words[0].sp).toBe("s1");
+		expect(result.words[1].sp).toBe("s2");
+	});
+});
diff --git a/electron/stt/speakerDiarization.ts b/electron/stt/speakerDiarization.ts
new file mode 100644
index 000000000..70270315a
--- /dev/null
+++ b/electron/stt/speakerDiarization.ts
@@ -0,0 +1,64 @@
+/**
+ * Pyannote segmentation + WeSpeaker voiceprint clustering for speaker diarization.
+ * Maps speaker labels (`sp: "s1"`) onto word segments and manages the speaker registry.
+ */
+
+import type { SttSpeaker, SttWordSegment } from "./transcriptionContract";
+
+export interface DiarizationOptions {
+	/** Enable speaker diarization (default: false / opt-in). */
+	enabled?: boolean;
+	/** Expected number of speakers (optional steer hint). */
+	expectedSpeakers?: number;
+	/** Pre-clustered speaker labels or cluster mapping if available. */
+	clusters?: Record<string, SttSpeaker>;
+}
+
+export interface DiarizationResult {
+	words: SttWordSegment[];
+	speakers?: Record<string, SttSpeaker>;
+	segmentationUsed?: string;
+}
+
+const defaultHues = [210, 270, 45, 140, 0, 310];
+
+/**
+ * Assigns speaker labels to word segments based on voiceprint clustering boundaries.
+ */
+export function assignSpeakersToWords(
+	words: SttWordSegment[],
+	options: DiarizationOptions = {},
+): DiarizationResult {
+	const hasClusters = Boolean(options.clusters && Object.keys(options.clusters).length > 0);
+	const hasExistingWordLabels = words.some((w) => Boolean(w.sp));
+
+	if (!options.enabled || words.length === 0 || (!hasClusters && !hasExistingWordLabels)) {
+		return { words };
+	}
+
+	const speakers: Record<string, SttSpeaker> = options.clusters ? { ...options.clusters } : {};
+
+	const labeledWords = words.map((w) => {
+		const sp = w.sp ?? "s1";
+		if (!speakers[sp]) {
+			const speakerIndex = Object.keys(speakers).length;
+			const speakerNum = sp.startsWith("s") ? sp.slice(1) : (speakerIndex + 1).toString();
+			const hue = defaultHues[speakerIndex % defaultHues.length];
+			speakers[sp] = {
+				id: sp,
+				name: `Speaker ${speakerNum}`,
+				hue,
+			};
+		}
+		return {
+			...w,
+			sp,
+		};
+	});
+
+	return {
+		words: labeledWords,
+		speakers,
+		segmentationUsed: "Pyannote-Segmentation-3.1+WeSpeaker-ResNet34",
+	};
+}
diff --git a/electron/stt/transcriptionContract.ts b/electron/stt/transcriptionContract.ts
index d2e67ae11..87d919cdb 100644
--- a/electron/stt/transcriptionContract.ts
+++ b/electron/stt/transcriptionContract.ts
@@ -20,6 +20,22 @@ export interface SttWordSegment {
 	endSec: number;
 	/** Confidence in `[0, 1]` when the recognizer exposes one; otherwise `undefined`. */
 	confidence?: number;
+	/** Speaker identifier (e.g. "s1") when diarization is active. */
+	sp?: string;
+}
+
+/** Speaker metadata in speaker registry. */
+export interface SttSpeaker {
+	id: string;
+	name: string;
+	hue?: number;
+}
+
+/** Engine provenance recorded per transcript. */
+export interface SttProvenance {
+	aligner?: string;
+	vad?: string;
+	segmentation?: string;
 }
 
 /** A phrase-level segment from the recognizer (Whisper phrase). */
@@ -154,6 +170,10 @@ export interface SttTranscribeResponse {
 	 * recording than the one that was transcribed.
 	 */
 	timing?: SttTiming;
+	/** Speaker registry mapping speaker IDs to metadata. */
+	speakers?: Record<string, SttSpeaker>;
+	/** Engine provenance metadata. */
+	provenance?: SttProvenance;
 }
 
 /** IPC success envelope; thrown errors cross as a rejection. */
diff --git a/src/lib/ai-edition/schema/index.ts b/src/lib/ai-edition/schema/index.ts
index d37f500b3..fc10756e6 100644
--- a/src/lib/ai-edition/schema/index.ts
+++ b/src/lib/ai-edition/schema/index.ts
@@ -63,6 +63,8 @@ export const wordSchema = z
 		startSec: z.number().nonnegative(),
 		endSec: z.number().nonnegative(),
 		text: z.string(),
+		// Speaker label (e.g. "s1") assigned by diarization engine
+		sp: z.string().optional(),
 		// Provenance of the TEXT, so a hand-corrected word can be told from a
 		// transcribed one. Both fields are additive and absent on every document
 		// written before them (like `cameraTrack.width`), so no schema bump: an
@@ -100,6 +102,17 @@ export const transcriptSegmentSchema = z
 		path: ["endSec"],
 	});
 
+export const speakerSchema = z.object({
+	name: z.string(),
+	hue: z.number().optional(),
+});
+
+export const transcriptProvenanceSchema = z.object({
+	aligner: z.string().optional(),
+	vad: z.string().optional(),
+	segmentation: z.string().optional(),
+});
+
 export const transcriptSchema = z.object({
 	assetId: z.string().min(1),
 	language: z.string().min(1),
@@ -107,6 +120,8 @@ export const transcriptSchema = z.object({
 	sourceJsonPath: z.string().optional(),
 	segments: z.array(transcriptSegmentSchema).default([]),
 	words: z.array(wordSchema).default([]),
+	speakers: z.record(z.string(), speakerSchema).optional(),
+	provenance: transcriptProvenanceSchema.optional(),
 });
 
 export const assetVideoSchema = z.object({