Use one-off workers to process requests without blocking

src/asr.ts

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+import { pipeline } from '@xenova/transformers';
+import { parentPort } from 'worker_threads';
+import * as fs from 'node:fs';
+import wavefile from 'wavefile';
+import { spawn } from 'node:child_process';
+
+let whisperPipeline: any;
+
+export async function canDiarization(): Promise<boolean> {
+	return new Promise((resolve) => {
+		const proc = spawn('python3', ['-c', 'import pyannote.audio']);
+		proc.on('close', (code: number) => resolve(code === 0));
+		proc.on('error', () => resolve(false));
+	});
+}
+
+async function runDiarization(audioPath: string, torchHome: string): Promise<any[]> {
+	const script = `
+import sys
+import json
+import os
+from pyannote.audio import Pipeline
+
+os.environ['TORCH_HOME'] = "${torchHome}"
+pipeline = Pipeline.from_pretrained("pyannote/speaker-diarization-3.1")
+diarization = pipeline(sys.argv[1])
+
+segments = []
+for turn, _, speaker in diarization.itertracks(yield_label=True):
+    segments.append({
+        "start": turn.start,
+        "end": turn.end,
+        "speaker": speaker
+    })
+
+print(json.dumps(segments))
+`;
+
+	return new Promise((resolve, reject) => {
+		let output = '';
+		const proc = spawn('python3', ['-c', script, audioPath]);
+		proc.stdout.on('data', (data: Buffer) => output += data.toString());
+		proc.stderr.on('data', (data: Buffer) => console.error(data.toString()));
+		proc.on('close', (code: number) => {
+			if(code === 0) {
+				try {
+					resolve(JSON.parse(output));
+				} catch (err) {
+					reject(new Error('Failed to parse diarization output'));
+				}
+			} else {
+				reject(new Error(`Python process exited with code ${code}`));
+			}
+		});
+		proc.on('error', reject);
+	});
+}
+
+function combineSpeakerTranscript(chunks: any[], speakers: any[]): string {
+	const speakerMap = new Map();
+	let speakerCount = 0;
+	speakers.forEach((seg: any) => {
+		if(!speakerMap.has(seg.speaker)) speakerMap.set(seg.speaker, ++speakerCount);
+	});
+
+	const lines: string[] = [];
+	let currentSpeaker = -1;
+	let currentText = '';
+	chunks.forEach((chunk: any) => {
+		const time = chunk.timestamp[0];
+		const speaker = speakers.find((s: any) => time >= s.start && time <= s.end);
+		const speakerNum = speaker ? speakerMap.get(speaker.speaker) : 1;
+		if (speakerNum !== currentSpeaker) {
+			if(currentText) lines.push(`[speaker ${currentSpeaker}]: ${currentText.trim()}`);
+			currentSpeaker = speakerNum;
+			currentText = chunk.text;
+		} else {
+			currentText += chunk.text;
+		}
+	});
+	if(currentText) lines.push(`[speaker ${currentSpeaker}]: ${currentText.trim()}`);
+	return lines.join('\n');
+}
+
+parentPort?.on('message', async ({ path, model, speaker, torchHome }) => {
+	try {
+		if(!whisperPipeline) whisperPipeline = await pipeline('automatic-speech-recognition', `Xenova/${model}`, {cache_dir: torchHome, quantized: true});
+
+		// Prepare audio file (convert to mono channel wave)
+		const wav = new wavefile.WaveFile(fs.readFileSync(path));
+		wav.toBitDepth('32f');
+		wav.toSampleRate(16000);
+		const samples = wav.getSamples();
+		let buffer;
+		if(Array.isArray(samples)) { // stereo to mono - average the channels
+			const left = samples[0];
+			const right = samples[1];
+			buffer = new Float32Array(left.length);
+			for (let i = 0; i < left.length; i++) buffer[i] = (left[i] + right[i]) / 2;
+		} else {
+			buffer = samples;
+		}
+
+		// Transcribe
+		const transcriptResult = await whisperPipeline(buffer, {return_timestamps: speaker ? 'word' : false});
+		if(!speaker) {
+			parentPort?.postMessage({ text: transcriptResult.text?.trim() || null });
+			return;
+		}
+
+		// Speaker Diarization
+		const hasDiarization = await canDiarization();
+		if(!hasDiarization) {
+			parentPort?.postMessage({ text: transcriptResult.text?.trim() || null, warning: 'Speaker diarization unavailable' });
+			return;
+		}
+
+		const speakers = await runDiarization(path, torchHome);
+		const combined = combineSpeakerTranscript(transcriptResult.chunks || [], speakers);
+		parentPort?.postMessage({ text: combined });
+	} catch (err) {
+		parentPort?.postMessage({ error: (err as Error).message });
+	}
+});