Fix large stereo issue

Author: dy

packages/encode-mp3/mp3-encode.js

@@ -27,12 +27,31 @@ export default async function mp3(opts) {
 
 	encoder.configure(cfg)
 
+	// WASM encoder has ~320MB/channel buffer limit.
+	// Chunk large inputs in 1152*1024 (~1.18M) sample blocks.
+	const CHUNK = 1152 * 1024
+
 	return { encode, flush, free }
 
 	function encode(ch) {
-		// returned buffer is owned by encoder — must copy
-		let raw = encoder.encode(ch)
-		return new Uint8Array(raw)
+		let n = ch[0].length
+		if (n <= CHUNK) {
+			let raw = encoder.encode(ch)
+			return new Uint8Array(raw)
+		}
+		let parts = []
+		for (let i = 0; i < n; i += CHUNK) {
+			let end = Math.min(i + CHUNK, n)
+			let slice = ch.map(c => c.subarray(i, end))
+			let raw = encoder.encode(slice)
+			if (raw.length) parts.push(new Uint8Array(raw))
+		}
+		let total = 0
+		for (let p of parts) total += p.length
+		let out = new Uint8Array(total)
+		let off = 0
+		for (let p of parts) { out.set(p, off); off += p.length }
+		return out
 	}
 
 	function flush() {

packages/encode-mp3/test.js

@@ -29,3 +29,14 @@ t('VBR mode', async () => {
 	let buf = enc.flush()
 	ok(buf.length > 0)
 })
+
+t('large stereo (30min 48kHz)', async () => {
+	let sr = 48000, dur = 1800, n = sr * dur
+	let ch = new Float32Array(n)
+	for (let i = 0; i < n; i++) ch[i] = 0.3 * Math.sin(2 * Math.PI * 440 * i / sr)
+	let enc = await mp3({ sampleRate: sr, channels: 2, bitrate: 128 })
+	let out = enc.encode([ch, new Float32Array(ch)])
+	ok(out.length > 0, 'has encoded data: ' + (out.length / 1e6).toFixed(1) + 'MB')
+	let final = enc.flush()
+	ok(out.length + final.length > 1e6, 'total > 1MB')
+})