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[Refactor] improve the JS example #588

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[Refactor] improve the JS example #588

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63 changes: 48 additions & 15 deletions samples/js/live-audio-transcription-example/app.js
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Original file line number Diff line number Diff line change
Expand Up @@ -39,9 +39,10 @@ console.log('Loading model...');
await model.load();
console.log('✓ Model loaded');

// Create live transcription session
// Create live transcription session (same pattern as C# sample).
const audioClient = model.createAudioClient();
const session = audioClient.createLiveTranscriptionSession();

session.settings.sampleRate = 16000; // Default is 16000; shown here for clarity
session.settings.channels = 1;
session.settings.bitsPerSample = 16;
Expand All @@ -56,10 +57,12 @@ const readPromise = (async () => {
try {
for await (const result of session.getTranscriptionStream()) {
const text = result.content?.[0]?.text;
if (!text) continue;

// `is_final` is a transcript-state marker only. It should not stop the app.
if (result.is_final) {
console.log();
console.log(` [FINAL] ${text}`);
} else if (text) {
process.stdout.write(`\n [FINAL] ${text}\n`);
} else {
process.stdout.write(text);
}
}
Expand Down Expand Up @@ -88,22 +91,52 @@ try {
? portAudio.SampleFormat16Bit
: portAudio.SampleFormat32Bit,
sampleRate: session.settings.sampleRate,
framesPerBuffer: 1600, // 100ms chunks
maxQueue: 15 // buffer during event-loop blocks from sync FFI calls
// Larger chunk size lowers callback frequency and reduces overflow risk.
framesPerBuffer: 3200,
// Allow deeper native queue during occasional event-loop stalls.
maxQueue: 64
}
});

let appendPending = false;
const appendQueue = [];
let pumping = false;
let warnedQueueDrop = false;

const pumpAudio = async () => {
if (pumping) return;
pumping = true;
try {
while (appendQueue.length > 0) {
const pcm = appendQueue.shift();
await session.append(pcm);
}
} catch (err) {
console.error('append error:', err.message);
} finally {
pumping = false;
// Handle race where new data arrived after loop exit.
if (appendQueue.length > 0) {
void pumpAudio();
}
}
};

audioInput.on('data', (buffer) => {
if (appendPending) return; // drop frame while backpressured
const pcm = new Uint8Array(buffer);
appendPending = true;
session.append(pcm).then(() => {
appendPending = false;
}).catch((err) => {
appendPending = false;
console.error('append error:', err.message);
});
const copy = new Uint8Array(pcm.length);
copy.set(pcm);
Comment on lines 125 to +127
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Copilot AI Apr 4, 2026

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In the audio data handler you’re copying the PCM buffer twice (new Uint8Array(buffer) already copies when buffer is a Node Buffer/TypedArray, and then you allocate/copy again into copy). This adds avoidable work on a hot path and can increase overflow risk under load. Consider doing a single copy into the queued Uint8Array (or creating a view + one explicit copy if you need to detach from a reused native buffer).

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// Keep a bounded queue to avoid unbounded memory growth.
if (appendQueue.length >= 100) {
appendQueue.shift();
if (!warnedQueueDrop) {
warnedQueueDrop = true;
console.warn('Audio append queue overflow; dropping oldest chunk to keep stream alive.');
}
}

appendQueue.push(copy);
void pumpAudio();
});

console.log();
Expand Down
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